Apache Pulsar Reference Guide

This reference guide demonstrates how your Quarkus application can utilize Quarkus Messaging to interact with Apache Pulsar.

1. Introduction

Apache Pulsar is an open-source, distributed messaging and streaming platform built for the cloud. It provides a multi-tenant, high-performance solution to server messaging with tiered storage capabilities.

Pulsar implements the publish-subscribe pattern:

Producers publish messages to topics.
Consumers create subscriptions to those topics to receive and process incoming messages, and send acknowledgments to the broker when processing is finished.
When a subscription is created, Pulsar retains all messages, even if the consumer is disconnected. The retained messages are discarded only when a consumer acknowledges that all these messages are processed successfully.

A Pulsar cluster consists of

One or more brokers, which are stateless components.
A metadata store for maintaining topic metadata, schema, coordination and cluster configuration.
A set of bookies used for persistent storage of messages.

2. Quarkus Extension for Apache Pulsar

Quarkus provides support for Apache Pulsar through SmallRye Reactive Messaging framework. Based on Eclipse MicroProfile Reactive Messaging specification 3.0, it proposes a flexible programming model bridging CDI and event-driven.

Note	This guide provides an in-depth look on Apache Pulsar and SmallRye Reactive Messaging framework. For a quick start take a look at Getting Started to Quarkus Messaging with Apache Pulsar.

You can add the messaging-pulsar extensions to your project by running the following command in your project base directory:

{includes}/devtools/extension-add.adoc

This will add the following to your build file:

pom.xml

<dependency>
    <groupId>io.quarkus</groupId>
    <artifactId>quarkus-messaging-pulsar</artifactId>
</dependency>

build.gradle

implementation("io.quarkus:quarkus-messaging-pulsar")

Note	The extension includes `pulsar-clients-original` version 3.0.0 as a transitive dependency and is compatible with Pulsar brokers version 2.10.x.

3. Configuring SmallRye Pulsar Connector

Because SmallRye Reactive Messaging framework supports different messaging backends like Apache Kafka, Apache Pulsar, AMQP, Apache Camel, JMS, MQTT, etc., it employs a generic vocabulary:

Applications send and receive messages. Message wraps a payload and can be extended with some metadata. This should not be confused with a Pulsar Message, which consists of value, key With the Pulsar connector, a Reactive Messaging message corresponds to a Pulsar message.
Messages transit on channels. Application components connect to channels to publish and consume messages. The Pulsar connector maps channels to Pulsar topics.
Channels are connected to message backends using connectors. Connectors are configured to map incoming messages to a specific channel (consumed by the application) and collect outgoing messages sent to a specific channel. Each connector is dedicated to a specific messaging technology. For example, the connector dealing with Pulsar is named smallrye-pulsar.

A minimal configuration for the Pulsar connector with an incoming channel looks like the following:

%prod.pulsar.client.serviceUrl=pulsar:6650 (1)
mp.messaging.incoming.prices.connector=smallrye-pulsar (2)

Configure the Pulsar broker service url for the production profile. You can configure it globally or per channel using mp.messaging.incoming.$channel.serviceUrl property. In dev mode and when running tests, [pulsar-dev-services] automatically starts a Pulsar broker.
Configure the connector to manage the prices channel. By default, the topic name is same as the channel name.

You can configure the topic attribute to override it.

Note	The `%prod` prefix indicates that the property is only used when the application runs in prod mode (so not in dev or test). Refer to the Profile documentation for further details.

Tip

Connector auto-attachment

If you have a single connector on your classpath, you can omit the connector attribute configuration. Quarkus automatically associates orphan channels to the (unique) connector found on the classpath. Orphan channels are outgoing channels without a downstream consumer or incoming channels without an upstream producer.

This auto-attachment can be disabled using:

quarkus.messaging.auto-connector-attachment=false

For more configuration options see Configuring Pulsar clients.

4. Receiving messages from Pulsar

The Pulsar Connector connects to a Pulsar broker using a Pulsar client and creates consumers to receive messages from Pulsar brokers, and it maps each Pulsar Message into Reactive Messaging Message.

4.1. Example

Let’s imagine you have a Pulsar broker running, and accessible using the pulsar:6650 address. Configure your application to receive Pulsar messages on the prices channel as follows:

mp.messaging.incoming.prices.serviceUrl=pulsar://pulsar:6650 # (1)
mp.messaging.incoming.prices.subscriptionInitialPosition=Earliest # (2)

Configure the Pulsar broker service url.
Make sure consumer subscription starts receiving messages from the Earliest position.

Note	You don’t need to set the Pulsar topic, nor the consumer name. By default, the connector uses the channel name (`prices`). You can configure the `topic` and `consumerName` attributes to override them.

Note	In Pulsar, consumers need to provide a `subscriptionName` for topic subscriptions. If not provided the connector generates a unique subscription name.

Then, your application can receive the double payload directly:

import org.eclipse.microprofile.reactive.messaging.Incoming;

import jakarta.enterprise.context.ApplicationScoped;

@ApplicationScoped
public class PriceConsumer {

    @Incoming("prices")
    public void consume(double price) {
        // process your price.
    }

}

Or, you can retrieve the Reactive Messaging type Message<Double>:

@Incoming("prices")
public CompletionStage<Void> consume(Message<Double> msg) {
    // access record metadata
    var metadata = msg.getMetadata(PulsarIncomingMessageMetadata.class).orElseThrow();
    // process the message payload.
    double price = msg.getPayload();
    // Acknowledge the incoming message (acknowledge the Pulsar message back to the broker)
    return msg.ack();
}

The Reactive Messaging Message type lets the consuming method access the incoming message metadata and handle the acknowledgment manually.

If you want to access the Pulsar message objects directly, use:

@Incoming("prices")
public void consume(org.apache.pulsar.client.api.Message<Double> msg) {
    String key = msg.getKey();
    String value = msg.getValue();
    String topic = msg.topicName();
    // ...
}

org.apache.pulsar.client.api.Message is provided by the underlying Pulsar client and can be used directly with the consumer method.

Alternatively, your application can inject a Multi in your bean, identified with the channel name and subscribe to its events as the following example:

import io.smallrye.mutiny.Multi;
import org.eclipse.microprofile.reactive.messaging.Channel;

import jakarta.inject.Inject;
import jakarta.ws.rs.GET;
import jakarta.ws.rs.Path;
import jakarta.ws.rs.Produces;
import jakarta.ws.rs.core.MediaType;
import org.jboss.resteasy.reactive.RestStreamElementType;

@Path("/prices")
public class PriceResource {

    @Inject
    @Channel("prices")
    Multi<Double> prices;

    @GET
    @Path("/prices")
    @RestStreamElementType(MediaType.TEXT_PLAIN)
    public Multi<Double> stream() {
        return prices;
    }
}

Note	When consuming messages with `@Channel`, the application code is responsible for the subscription. In the example above, the Quarkus REST (formerly RESTEasy Reactive) endpoint handles that for you.

Following types can be injected as channels:

@Inject @Channel("prices") Multi<Double> streamOfPayloads;

@Inject @Channel("prices") Multi<Message<Double>> streamOfMessages;

@Inject @Channel("prices") Publisher<Double> publisherOfPayloads;

@Inject @Channel("prices") Publisher<Message<Double>> publisherOfMessages;

As with the previous Message example, if your injected channel receives payloads (Multi<T>), it acknowledges the message automatically, and support multiple subscribers. If your injected channel receives Message (Multi<Message<T>>), you will be responsible for the acknowledgment and broadcasting.

4.2. Blocking processing

Reactive Messaging invokes your method on an I/O thread. See the Quarkus Reactive Architecture documentation for further details on this topic. But, you often need to combine Reactive Messaging with blocking processing such as database interactions. For this, you need to use the @Blocking annotation indicating that the processing is blocking and should not be run on the caller thread.

For example, The following code illustrates how you can store incoming payloads to a database using Hibernate with Panache:

import io.smallrye.reactive.messaging.annotations.Blocking;
import org.eclipse.microprofile.reactive.messaging.Incoming;

import jakarta.enterprise.context.ApplicationScoped;
import jakarta.transaction.Transactional;

@ApplicationScoped
public class PriceStorage {

    @Incoming("prices")
    @Transactional
    public void store(int priceInUsd) {
        Price price = new Price();
        price.value = priceInUsd;
        price.persist();
    }

}

Note

There are 2 @Blocking annotations:

io.smallrye.reactive.messaging.annotations.Blocking
io.smallrye.common.annotation.Blocking

They have the same effect. Thus, you can use both. The first one provides more fine-grained tuning such as the worker pool to use and whether it preserves the order. The second one, used also with other reactive features of Quarkus, uses the default worker pool and preserves the order.

Detailed information on the usage of @Blocking annotation can be found in SmallRye Reactive Messaging – Handling blocking execution.

Tip	@RunOnVirtualThread For running the blocking processing on Java virtual threads, see the Quarkus Virtual Thread support with Reactive Messaging documentation.

Tip	@Transactional If your method is annotated with `@Transactional`, it will be considered blocking automatically, even if the method is not annotated with `@Blocking`.

4.3. Pulsar Subscription Types

Pulsar subscriptionType consumer configuration can be used flexibly to achieve different messaging scenarios, such as publish-subscribe or queuing.

Exclusive subscription type allows specifying a unique subscription name for "fan-out pub-sub messaging". This is the default subscription type.
Shared, Key_Shared or Failover subscription types allow multiple consumers to share the same subscription name, to achieve "message queuing" among consumers.

If a subscription name is not provided Quarkus generates a unique id.

4.4. Deserialization and Pulsar Schema

The Pulsar Connector allows configuring Schema configuration for the underlying Pulsar consumer. See the Pulsar Schema Configuration & Auto Schema Discovery for more information.

4.5. Acknowledgement Strategies

When a message produced from a Pulsar Message is acknowledged, the connector sends an acknowledgement request to the Pulsar broker. All Reactive Messaging messages need to be acknowledged, which is handled automatically in most cases. Acknowledgement requests can be sent to the Pulsar broker using the following two strategies:

Individual acknowledgement is the default strategy, an acknowledgement request is to the broker for each message.
Cumulative acknowledgement, configured using ack-strategy=cumulative, the consumer only acknowledges the last message it received. All messages in the stream up to (and including) the provided message are not redelivered to that consumer.

Note	By default, the Pulsar consumer does not wait for the acknowledgement confirmation from the broker to validate an acknowledgement. You can enable this using `ackReceiptEnabled=true`.

4.6. Failure Handling Strategies

If a message produced from a Pulsar message is nacked, a failure strategy is applied. The Quarkus Pulsar extension supports 4 strategies:

nack (default) sends negative acknowledgment to the broker, triggering the broker to redeliver this message to the consumer. The negative acknowledgment can be further configured using negativeAckRedeliveryDelayMicros and negativeAck.redeliveryBackoff properties.
fail fail the application, no more messages will be processed.
ignore the failure is logged, but the acknowledgement strategy will be applied and the processing will continue.
continue the failure is logged, but processing continues without applying acknowledgement or negative acknowledgement. This strategy can be used with Acknowledgement timeout configuration.
reconsume-later sends the message to the retry letter topic using the reconsumeLater API to be reconsumed with a delay. The delay can be configured using the reconsumeLater.delay property and defaults to 3 seconds. Custom delay or properties per message can be configured by adding an instance of io.smallrye.reactive.messaging.pulsar.PulsarReconsumeLaterMetadata to the failure metadata.

4.6.1. Acknowledgement timeout

Similar to the negative acknowledgement, with the acknowledgement timeout mechanism, the Pulsar client tracks the unacknowledged messages, for the given ackTimeout period and sends redeliver unacknowledged messages request to the broker, thus the broker resends the unacknowledged messages to the consumer.

To configure the timeout and redelivery backoff mechanism you can set ackTimeoutMillis and ackTimeout.redeliveryBackoff properties. The ackTimeout.redeliveryBackoff value accepts comma separated values of min delay in milliseconds, max delay in milliseconds and multiplier respectively:

mp.messaging.incoming.out.failure-strategy=continue
mp.messaging.incoming.out.ackTimeoutMillis=10000
mp.messaging.incoming.out.ackTimeout.redeliveryBackoff=1000,60000,2

4.6.2. Reconsume later and retry letter topic

The retry letter topic pushes messages that are not consumed successfully to a dead letter topic and continue message consumption. Note that dead letter topic can be used in different message redelivery methods, such as acknowledgment timeout, negative acknowledgment or retry letter topic.

mp.messaging.incoming.data.failure-strategy=reconsume-later
mp.messaging.incoming.data.reconsumeLater.delay=5000
mp.messaging.incoming.data.retryEnable=true
mp.messaging.incoming.data.negativeAck.redeliveryBackoff=1000,60000,2

4.6.3. Dead-letter topic

The dead letter topic pushes messages that are not consumed successfully to a dead letter topic an continue message consumption. Note that dead letter topic can be used in different message redelivery methods, such as acknowledgment timeout, negative acknowledgment or retry letter topic.

mp.messaging.incoming.data.failure-strategy=nack
mp.messaging.incoming.data.deadLetterPolicy.maxRedeliverCount=2
mp.messaging.incoming.data.deadLetterPolicy.deadLetterTopic=my-dead-letter-topic
mp.messaging.incoming.data.deadLetterPolicy.initialSubscriptionName=my-dlq-subscription
mp.messaging.incoming.data.subscriptionType=Shared

Important

Negative acknowledgment or acknowledgment timeout methods for redelivery will redeliver the whole batch of messages containing at least an unprocessed message. See Producer Batching for more information.

4.7. Receiving Pulsar Messages in Batches

By default, incoming methods receive each Pulsar message individually. You can enable batch mode using batchReceive=true property, or setting a batchReceivePolicy in consumer configuration.

@Incoming("prices")
public CompletionStage<Void> consumeMessage(Message<org.apache.pulsar.client.api.Messages<Double>> messages) {
    for (org.apache.pulsar.client.api.Message<Double> msg : messages.getPayload()) {
        String key = msg.getKey();
        String topic = msg.getTopicName();
        long timestamp = msg.getEventTime();
        //... process messages
    }
    // ack will commit the latest offsets (per partition) of the batch.
    return messages.ack();
}

@Incoming("prices")
public void consumeRecords(org.apache.pulsar.client.api.Messages<Double> messages) {
    for (org.apache.pulsar.client.api.Message<Double> msg : messages) {
        //... process messages
    }
}

Or you can directly receive the list of payloads to the consume method:

@Incoming("prices")
public void consume(List<Double> prices) {
    for (double price : prices) {
        // process price
    }
}

Note	Quarkus auto-detects batch types for incoming channels and sets batch configuration automatically. You can configure batch mode explicitly with `mp.messaging.incoming.$channel.batchReceive` property.

5. Sending messages to Pulsar

The Pulsar Connector can write Reactive Messaging `Message`s as Pulsar Message.

5.1. Example

Let’s imagine you have a Pulsar broker running, and accessible using the pulsar:6650 address. Configure your application to write the messages from the prices channel into a Pulsar Messages as follows:

mp.messaging.outgoing.prices.serviceUrl=pulsar://pulsar:6650 # (1)

Configure the Pulsar broker service url.

Note	You don’t need to set the Pulsar topic, nor the producer name. By default, the connector uses the channel name (`prices`). You can configure the `topic` and `producerName` attributes to override them.

Then, your application must send Message<Double> to the prices channel. It can use double payloads as in the following snippet:

import io.smallrye.mutiny.Multi;
import org.eclipse.microprofile.reactive.messaging.Outgoing;

import jakarta.enterprise.context.ApplicationScoped;
import java.time.Duration;
import java.util.Random;

@ApplicationScoped
public class PulsarPriceProducer {

    private final Random random = new Random();

    @Outgoing("prices-out")
    public Multi<Double> generate() {
        // Build an infinite stream of random prices
        // It emits a price every second
        return Multi.createFrom().ticks().every(Duration.ofSeconds(1))
            .map(x -> random.nextDouble());
    }

}

Note that the generate method returns a Multi<Double>, which implements the Flow.Publisher interface. This publisher will be used by the framework to generate messages and send them to the configured Pulsar topic.

Instead of returning a payload, you can return a io.smallrye.reactive.messaging.pulsar.OutgoingMessage to send Pulsar messages:

@Outgoing("out")
public Multi<OutgoingMessage<Double>> generate() {
    return Multi.createFrom().ticks().every(Duration.ofSeconds(1))
        .map(x -> OutgoingMessage.of("my-key", random.nextDouble()));
}

Payload can be wrapped inside org.eclipse.microprofile.reactive.messaging.Message to have more control on the written records:

@Outgoing("generated-price")
public Multi<Message<Double>> generate() {
    return Multi.createFrom().ticks().every(Duration.ofSeconds(1))
            .map(x -> Message.of(random.nextDouble())
                    .addMetadata(PulsarOutgoingMessageMetadata.builder()
                            .withKey("my-key")
                            .withProperties(Map.of("property-key", "value"))
                            .build()));
}

When sending Messages, you can add an instance of io.smallrye.reactive.messaging.pulsar.PulsarOutgoingMessageMetadata to influence how the message is going to be written to Pulsar.

Other than method signatures returning a Flow.Publisher, outgoing method can also return single message. In this case the producer will use this method as generator to create an infinite stream.

@Outgoing("prices-out") T generate(); // T excluding void

@Outgoing("prices-out") Message<T> generate();

@Outgoing("prices-out") Uni<T> generate();

@Outgoing("prices-out") Uni<Message<T>> generate();

@Outgoing("prices-out") CompletionStage<T> generate();

@Outgoing("prices-out") CompletionStage<Message<T>> generate();

5.2. Serialization and Pulsar Schema

The Pulsar Connector allows configuring Schema configuration for the underlying Pulsar producer. See the Pulsar Schema Configuration & Auto Schema Discovery for more information.

5.3. Sending key/value pairs

In order to send Kev/Value pairs to Pulsar, you can configure the Pulsar producer Schema with a KeyValue schema.

package pulsar.outbound;

import jakarta.enterprise.context.ApplicationScoped;
import jakarta.enterprise.inject.Produces;

import org.apache.pulsar.client.api.Schema;
import org.apache.pulsar.common.schema.KeyValue;
import org.eclipse.microprofile.reactive.messaging.Incoming;
import org.eclipse.microprofile.reactive.messaging.Outgoing;

import io.smallrye.common.annotation.Identifier;

@ApplicationScoped
public class PulsarKeyValueExample {

    @Identifier("out")
    @Produces
    Schema<KeyValue<String, Long>> schema = Schema.KeyValue(Schema.STRING, Schema.INT64);

    @Incoming("in")
    @Outgoing("out")
    public KeyValue<String, Long> process(long in) {
        return new KeyValue<>("my-key", in);
    }

}

If you need more control on the written records, use PulsarOutgoingMessageMetadata.

5.4. Acknowledgement

Upon receiving a message from a Producer, a Pulsar broker assigns a MessageId to the message and sends it back to the producer, confirming that the message is published.

By default, the connector does wait for Pulsar to acknowledge the record to continue the processing (acknowledging the received Message). You can disable this by setting the waitForWriteCompletion attribute to false.

If a record cannot be written, the message is nacked.

Important

The Pulsar client automatically retries sending messages in case of failure, until the send timeout is reached. The send timeout is configurable with sendTimeoutMs attribute and by default is 30 seconds.

5.5. Back-pressure and inflight records

The Pulsar outbound connector handles back-pressure, monitoring the number of pending messages waiting to be written to the Pulsar broker. The number of pending messages is configured using the maxPendingMessages attribute and defaults to 1000.

The connector only sends that amount of messages concurrently. No other messages will be sent until at least one pending message gets acknowledged by the broker. Then, the connector writes a new message to Pulsar when one of the broker’s pending messages get acknowledged.

You can also remove the limit of pending messages by setting maxPendingMessages to 0. Note that Pulsar also enables to configure the number of pending messages per partition using maxPendingMessagesAcrossPartitions.

5.6. Producer Batching

By default, the Pulsar producer batches individual messages together to be published to the broker. You can configure batching parameters using batchingMaxPublishDelayMicros, batchingPartitionSwitchFrequencyByPublishDelay, batchingMaxMessages, batchingMaxBytes configuration properties, or disable it completely with batchingEnabled=false.

When using Key_Shared consumer subscriptions, the batcherBuilder can be configured to BatcherBuilder.KEY_BASED.

6. Pulsar Transactions and Exactly-Once Processing

Pulsar transactions enable event streaming applications to consume, process, and produce messages in one atomic operation.

Transactions allow one or multiple producers to send batch of messages to multiple topics where all messages in the batch are eventually visible to any consumer, or none is ever visible to consumers.

Important

In order to be used, transaction support needs to be activated on the broker configuration, using transactionCoordinatorEnabled=true and systemTopicEnabled=true broker configuration.

On the client side, the transaction support also needs to be enabled on PulsarClient configuration:

mp.messaging.outgoing.tx-producer.enableTransaction=true

Pulsar connector provides PulsarTransactions custom emitter for writing records inside a transaction.

It can be used as a regular emitter @Channel:

package pulsar.outbound;

import jakarta.enterprise.context.ApplicationScoped;
import jakarta.inject.Inject;

import org.eclipse.microprofile.reactive.messaging.Channel;
import org.eclipse.microprofile.reactive.messaging.Incoming;
import org.eclipse.microprofile.reactive.messaging.Message;

import io.smallrye.mutiny.Uni;
import io.smallrye.reactive.messaging.pulsar.OutgoingMessage;
import io.smallrye.reactive.messaging.pulsar.transactions.PulsarTransactions;

@ApplicationScoped
public class PulsarTransactionalProducer {

    @Inject
    @Channel("tx-out-example")
    PulsarTransactions<OutgoingMessage<Integer>> txProducer;

    @Inject
    @Channel("other-producer")
    PulsarTransactions<String> producer;

    @Incoming("in")
    public Uni<Void> emitInTransaction(Message<Integer> in) {
        return txProducer.withTransaction(emitter -> {
            emitter.send(OutgoingMessage.of("a", 1));
            emitter.send(OutgoingMessage.of("b", 2));
            emitter.send(OutgoingMessage.of("c", 3));
            producer.send(emitter, "4");
            producer.send(emitter, "5");
            producer.send(emitter, "6");
            return Uni.createFrom().completionStage(in::ack);
        });
    }

}

The function given to the withTransaction method receives a TransactionalEmitter for producing records, and returns a Uni that provides the result of the transaction. If the processing completes successfully, the producer is flushed and the transaction is committed. If the processing throws an exception, returns a failing Uni, or marks the TransactionalEmitter for abort, the transaction is aborted.

Note	Multiple transactional producers can participate in a single transaction. This ensures all messages are sent using the started transaction and before the transaction is committed, all participating producers are flushed.

If this method is called on a Vert.x context, the processing function is also called on that context. Otherwise, it is called on the sending thread of the producer.

6.1. Exactly-Once Processing

Pulsar Transactions API also allows managing consumer offsets inside a transaction, together with produced messages. This in turn enables coupling a consumer with a transactional producer in a consume-transform-produce pattern, also known as exactly-once processing. It means that an application consumes messages, processes them, publishes the results to a topic, and commits offsets of the consumed messages in a transaction.

The PulsarTransactions emitter also provides a way to apply exactly-once processing to an incoming Pulsar message inside a transaction.

The following example includes a batch of Pulsar messages inside a transaction.

mp.messaging.outgoing.tx-out-example.enableTransaction=true
# ...
mp.messaging.incoming.in-channel.enableTransaction=true
mp.messaging.incoming.in-channel.batchReceive=true

package pulsar.outbound;

import jakarta.enterprise.context.ApplicationScoped;
import jakarta.inject.Inject;

import org.apache.pulsar.client.api.Messages;
import org.eclipse.microprofile.reactive.messaging.Channel;
import org.eclipse.microprofile.reactive.messaging.Incoming;
import org.eclipse.microprofile.reactive.messaging.Message;

import io.smallrye.mutiny.Uni;
import io.smallrye.reactive.messaging.pulsar.transactions.PulsarTransactions;

    @ApplicationScoped
    public class PulsarExactlyOnceProcessor {

        @Inject
        @Channel("tx-out-example")
        PulsarTransactions<Integer> txProducer;

        @Incoming("in-channel")
        public Uni<Void> emitInTransaction(Message<Messages<Integer>> batch) {
            return txProducer.withTransactionAndAck(batch, emitter -> {
                for (org.apache.pulsar.client.api.Message<Integer> record : batch.getPayload()) {
                    emitter.send(PulsarMessage.of(record.getValue() + 1, record.getKey()));
                }
                return Uni.createFrom().voidItem();
            });
        }

    }

If the processing completes successfully, the message is acknowledged inside the transaction and the transaction is committed.

Important

When using exactly-once processing, messages can only be acked individually rather than cumulatively.

If the processing needs to abort, the message is nack’ed. One of the failure strategies can be employed in order to retry the processing or simply fail-stop. Note that the Uni returned from the withTransaction will yield a failure if the transaction fails and is aborted.

The application can choose to handle the error case, but for the message consumption to continue, Uni returned from the @Incoming method must not result in failure. PulsarTransactions#withTransactionAndAck method will ack and nack the message but will not stop the reactive stream. Ignoring the failure simply resets the consumer to the last committed offsets and resumes the processing from there.

Important

In order to avoid duplicates in case of failure, it is recommended to enable message deduplication and batch index level acknowledgment on the broker side:

quarkus.pulsar.devservices.broker-config.brokerDeduplicationEnabled=true
quarkus.pulsar.devservices.broker-config.brokerDeduplicationEntriesInterval=1000
quarkus.pulsar.devservices.broker-config.brokerDeduplicationSnapshotIntervalSeconds=3000
quarkus.pulsar.devservices.broker-config.acknowledgmentAtBatchIndexLevelEnabled=3000

mp.messaging.incoming.data.batchIndexAckEnabled=true

7. Pulsar Schema Configuration & Auto Schema Discovery

Pulsar messages are stored with payloads as unstructured byte array. A Pulsar schema defines how to serialize structured data to the raw message bytes. The schema is applied in producers and consumers to write and read with an enforced data structure. It serializes data into raw bytes before they are published to a topic and deserializes the raw bytes before they are delivered to consumers.

Pulsar uses a schema registry as a central repository to store the registered schema information, which enables producers/consumers to coordinate the schema of a topic’s messages through brokers. By default the Apache BookKeeper is used to store schemas.

Pulsar API provides built-in schema information for a number of primitive types and complex types such as Key/Value, Avro and Protobuf.

The Pulsar Connector allows specifying the schema as a primitive type using the schema property:

mp.messaging.incoming.prices.connector=smallrye-pulsar
mp.messaging.incoming.prices.schema=INT32

mp.messaging.outgoing.prices-out.connector=smallrye-pulsar
mp.messaging.outgoing.prices-out.schema=DOUBLE

If the value for the schema property matches a Schema Type a simple schema will be created with that type and will be used for that channel.

The Pulsar Connector allows configuring complex schema types by providing Schema beans through CDI, identified with the @Identifier qualifier.

For example the following bean provides an JSON schema and a Key/Value schema:

package pulsar.configuration;

import jakarta.enterprise.context.ApplicationScoped;
import jakarta.enterprise.inject.Produces;

import org.apache.pulsar.client.api.Schema;
import org.apache.pulsar.common.schema.KeyValue;
import org.apache.pulsar.common.schema.KeyValueEncodingType;

import io.smallrye.common.annotation.Identifier;

@ApplicationScoped
public class PulsarSchemaProvider {

    @Produces
    @Identifier("user-schema")
    Schema<User> userSchema = Schema.JSON(User.class);

    @Produces
    @Identifier("a-channel")
    Schema<KeyValue<Integer, User>> keyValueSchema() {
        return Schema.KeyValue(Schema.INT32, Schema.JSON(User.class), KeyValueEncodingType.SEPARATED);
    }

    public static class User {
        String name;
        int age;

    }
}

To configure the incoming channel users with defined schema, you need to set the schema property to the identifier of the schema user-schema:

mp.messaging.incoming.users.connector=smallrye-pulsar
mp.messaging.incoming.users.schema=user-schema

If no schema property is found, the connector looks for Schema beans identified with the channel name. For example, the outgoing channel a-channel will use the key/value schema.

mp.messaging.outgoing.a-channel.connector=smallrye-pulsar

If no schema information is provided incoming channels will use Schema.AUTO_CONSUME(), whereas outgoing channels will use Schema.AUTO_PRODUCE_BYTES() schemas.

7.1. Auto Schema Discovery

When using Quarkus Messaging Pulsar (io.quarkus:quarkus-messaging-pulsar), Quarkus can often automatically detect the correct Pulsar Schema to configure. This autodetection is based on declarations of @Incoming and @Outgoing methods, as well as injected @Channels.

For example, if you declare

@Outgoing("generated-price")
public Multi<Integer> generate() {
    ...
}

and your configuration indicates that the generated-price channel uses the smallrye-pulsar connector, then Quarkus will automatically set the schema attribute of the generated-price channel to Pulsar Schema INT32.

Similarly, if you declare

@Incoming("my-pulsar-consumer")
public void consume(org.apache.pulsar.api.client.Message<byte[]> record) {
    ...
}

and your configuration indicates that the my-pulsar-consumer channel uses the smallrye-pulsar connector, then Quarkus will automatically set the schema attribute to Pulsar BYTES Schema.

Finally, if you declare

@Inject
@Channel("price-create")
Emitter<Double> priceEmitter;

and your configuration indicates that the price-create channel uses the smallrye-pulsar connector, then Quarkus will automatically set the schema to Pulsar INT64 Schema.

The full set of types supported by the Pulsar Schema autodetection is:

short and java.lang.Short
int and java.lang.Integer
long and java.lang.Long
float and java.lang.Float
double and java.lang.Double
byte[]
java.time.Instant
java.sql.Timestamp
java.time.LocalDate
java.time.LocalTime
java.time.LocalDateTime
java.nio.ByteBuffer
classes generated from Avro schemas, as well as Avro GenericRecord, will be configured with AVRO schema type
classes generated from Protobuf schemas, will be configured with PROTOBUF schema type
other classes will automatically be configured with JSON schema type

Note	Note that `JSON` schema type enforces schema validation.

In addition to those Pulsar-provided schemas, Quarkus provides following schema implementations without enforcing validation :

io.vertx.core.buffer.Buffer will be configured with io.quarkus.pulsar.schema.BufferSchema schema
io.vertx.core.json.JsonObject will be configured with io.quarkus.pulsar.schema.JsonObjectSchema schema
io.vertx.core.json.JsonArray will be configured with io.quarkus.pulsar.schema.JsonArraySchema schema
For schema-less Json serialization, if the schema configuration is set to ObjectMapper<fully_qualified_name_of_the_bean>, a Schema will be generated using the Jackson ObjectMapper, without enforcing a Pulsar Schema validation. io.quarkus.pulsar.schema.ObjectMapperSchema can be used to explicitly configure JSON schema without validation.

If a schema is set by configuration, it won’t be replaced by the auto-detection.

In case you have any issues with serializer auto-detection, you can switch it off completely by setting quarkus.messaging.pulsar.serializer-autodetection.enabled=false. If you find you need to do this, please file a bug in the Quarkus issue tracker so we can fix whatever problem you have.

pulsar-dev-services.adoc

8. Configuring Pulsar clients

Pulsar clients, consumers and producers are very customizable to configure how a Pulsar client application behaves.

The Pulsar connector creates a Pulsar client and, a consumer or a producer per channel, each with sensible defaults to ease their configuration. Although the creation is handled, all available configuration options remain configurable through Pulsar channels.

While idiomatic way of creating PulsarClient, PulsarConsumer or PulsarProducer are through builder APIs, in its essence those APIs build each time a configuration object, to pass onto the implementation. Those are ClientConfigurationData, ConsumerConfigurationData and ProducerConfigurationData.

Pulsar Connector allows receiving properties for those configuration objects directly. For example, the broker authentication information for PulsarClient is received using authPluginClassName and authParams properties. In order to configure the authentication for the incoming channel data :

mp.messaging.incoming.data.connector=smallrye-pulsar
mp.messaging.incoming.data.serviceUrl=pulsar://localhost:6650
mp.messaging.incoming.data.topic=topic
mp.messaging.incoming.data.subscriptionInitialPosition=Earliest
mp.messaging.incoming.data.schema=INT32
mp.messaging.incoming.data.authPluginClassName=org.apache.pulsar.client.impl.auth.AuthenticationBasic
mp.messaging.incoming.data.authParams={"userId":"superuser","password":"admin"}

Note that the Pulsar consumer property subscriptionInitialPosition is also configured with the Earliest value which represents with enum value SubscriptionInitialPosition.Earliest.

This approach covers most of the configuration cases. However, non-serializable objects such as CryptoKeyReader, ServiceUrlProvider etc. cannot be configured this way. The Pulsar Connector allows taking into account instances of Pulsar configuration data objects – ClientConfigurationData, ConsumerConfigurationData, ProducerConfigurationData:

import jakarta.enterprise.inject.Produces;
import io.smallrye.common.annotation.Identifier;
import org.apache.pulsar.client.impl.conf.ConsumerConfigurationData;

class PulsarConfig {

    @Produces
    @Identifier("my-consumer-options")
    public ConsumerConfigurationData<String> getConsumerConfig() {
        ConsumerConfigurationData<String> data = new ConsumerConfigurationData<>();
        data.setAckReceiptEnabled(true);
        data.setCryptoKeyReader(DefaultCryptoKeyReader.builder()
                //...
                .build());
        return data;
    }
}

This instance is retrieved and used to configure the client used by the connector. You need to indicate the name of the client using the client-configuration, consumer-configuration or producer-configuration attributes:

mp.messaging.incoming.prices.consumer-configuration=my-consumer-options

If no [client|consumer|producer]-configuration is configured, the connector will look for instances identified with the channel name:

import jakarta.enterprise.inject.Produces;
import io.smallrye.common.annotation.Identifier;
import org.apache.pulsar.client.impl.AutoClusterFailover;
import org.apache.pulsar.client.impl.conf.ClientConfigurationData;

class PulsarConfig {

    @Produces
    @Identifier("prices")
    public ClientConfigurationData getClientConfig() {
        ClientConfigurationData data = new ClientConfigurationData();
        data.setEnableTransaction(true);
        data.setServiceUrlProvider(AutoClusterFailover.builder()
                // ...
                .build());
        return data;
    }
}

You also can provide a Map<String, Object> containing configuration values by key:

import jakarta.enterprise.inject.Produces;
import io.smallrye.common.annotation.Identifier;
import org.apache.pulsar.client.api.BatcherBuilder;
import org.apache.pulsar.client.impl.conf.ClientConfigurationData;
import org.apache.pulsar.client.impl.customroute.PartialRoundRobinMessageRouterImpl;
import java.util.Map;

class PulsarConfig {

    @Produces
    @Identifier("prices")
    public Map<String, Object> getProducerConfig() {
        return Map.of(
                "batcherBuilder", BatcherBuilder.KEY_BASED,
                "sendTimeoutMs", 3000,
                "customMessageRouter", new PartialRoundRobinMessageRouterImpl(4));
    }
}

Different configuration sources are loaded in the following order of precedence, from the least important to the highest:

Map<String, Object> config map produced with default config identifier, default-pulsar-client, default-pulsar-consumer, default-pulsar-producer.
Map<String, Object> config map produced with identifier in the configuration or channel name
[Client|Producer|Consuemr]ConfigurationData object produced with identifier in the channel configuration or the channel name
Channel configuration properties named with [Client|Producer|Consuemr]ConfigurationData field names.

See Configuration Reference for the exhaustive list of configuration options.

8.1. Configuring Pulsar Authentication

Pulsar provides a pluggable authentication framework, and Pulsar brokers/proxies use this mechanism to authenticate clients.

Clients can be configured in application.properties file using authPluginClassName and authParams attributes:

pulsar.client.serviceUrl=pulsar://pulsar:6650
pulsar.client.authPluginClassName=org.apache.pulsar.client.impl.auth.AuthenticationBasic
pulsar.client.authParams={"userId":"superuser","password":"admin"}

Or programmatically:

import java.util.Map;

import jakarta.enterprise.inject.Produces;
import io.smallrye.common.annotation.Identifier;
import org.apache.pulsar.client.impl.conf.ClientConfigurationData;
import org.apache.pulsar.client.impl.auth.AuthenticationBasic;

class PulsarConfig {

    @Produces
    @Identifier("prices")
    public ClientConfigurationData config() {
        var data = new ClientConfigurationData();
        var auth = new AuthenticationBasic();
        auth.configure(Map.of("userId", "superuser", "password", "admin"));
        data.setAuthentication(auth);
        return data;
    }
}

8.1.1. Configuring authentication to Pulsar using mTLS

Pulsar Messaging extension integrates with the Quarkus TLS registry to authenticate clients using mTLS.

To configure the mTLS for a Pulsar channel, you need to provide a named TLS configuration in the application.properties:

quarkus.tls.my-tls-config.trust-store.p12.path=target/certs/pulsar-client-truststore.p12
quarkus.tls.my-tls-config.trust-store.p12.password=secret
quarkus.tls.my-tls-config.key-store.p12.path=target/certs/pulsar-client-keystore.p12
quarkus.tls.my-tls-config.key-store.p12.password=secret

mp.messaging.incoming.prices.tls-configuration-name=my-tls-config

8.1.2. Configuring access to Datastax Luna Streaming

Luna Streaming is a production-ready distribution of Apache Pulsar, with tools and support from DataStax. After creating your DataStax Luna Pulsar tenant, note the auto generated token, and configure the token authentication:

pulsar.client.serviceUrl=pulsar+ssl://pulsar-aws-eucentral1.streaming.datastax.com:6651
pulsar.client.authPluginClassName=org.apache.pulsar.client.impl.auth.AuthenticationToken
pulsar.client.authParams=token:eyJhbGciOiJSUzI1NiIsInR5cCI6IkpXVCJ9.eyJpYXQiOjE2ODY4MTc4MzQsImlzcyI6ImRhdGFzdGF4Iiwic3ViIjoiY2xpZW50OzA3NGZhOTI4LThiODktNDBhNC04MDEzLWNlNjVkN2JmZWIwZTtjSEpwWTJWejsyMDI5ODdlOGUyIiwidG9rZW5pZCI6IjIwMjk4N2U4ZTIifQ....

Make sure to create topics beforehand, or enable the Auto Topic Creation in the namespace configuration.

Note that the topic configuration needs to reference full name of topics:

mp.messaging.incoming.prices.topic=persistent://my-tenant/default/prices

8.1.3. Configuring access to StreamNative Cloud

StreamNative Cloud is a fully managed Pulsar-as-a-Service available in different deployment options, whether it is fully-hosted, on a public cloud but managed by StreamNative or self-managed on Kubernetes.

The StreamNative Pulsar clusters use Oauth2 authentication, so you need to make sure that a service account exists with required permissions to the Pulsar namespace/topic your application is using.

Next, you need to download the Key file (which serves as private key) of the service account and note the issuer URL (typically https://auth.streamnative.cloud/) and the audience (for example urn:sn:pulsar:o-rf3ol:redhat) for your cluster. The Pulsar Clients page in the Admin section in the StreamNative Cloud console helps you with this process.

To configure your application with Pulsar Oauth2 authentication:

pulsar.tenant=public
pulsar.namespace=default
pulsar.client.serviceUrl=pulsar+ssl://quarkus-71eaadbf-a6f3-4355-85d2-faf436b23d86.aws-euc1-prod-snci-pool-slug.streamnative.aws.snio.cloud:6651
pulsar.client.authPluginClassName=org.apache.pulsar.client.impl.auth.oauth2.AuthenticationOAuth2
pulsar.client.authParams={"type":"client_credentials","privateKey":"data:application/json;base64,<base64-encoded value>","issuerUrl":"https://auth.streamnative.cloud/","audience":"urn:sn:pulsar:o-rfwel:redhat"}

Note that the pulsar.client.authParams configuration contains a Json string with issuerUrl, audience and the privateKey in the data:application/json;base64,<base64-encoded-key-file> format.

Alternatively you can configure the authentication programmatically:

package org.acme.pulsar;

import java.net.MalformedURLException;
import java.net.URL;

import org.apache.pulsar.client.impl.auth.oauth2.AuthenticationFactoryOAuth2;
import org.apache.pulsar.client.impl.conf.ClientConfigurationData;
import org.eclipse.microprofile.config.inject.ConfigProperty;

import io.smallrye.common.annotation.Identifier;
import jakarta.enterprise.context.ApplicationScoped;
import jakarta.enterprise.inject.Produces;

@ApplicationScoped
public class PulsarAuth {

    @ConfigProperty(name = "pulsar.issuerUrl")
    String issuerUrl;

    @ConfigProperty(name = "pulsar.credentials")
    String credentials;

    @ConfigProperty(name = "pulsar.audience")
    String audience;

    @Produces
    @Identifier("pulsar-auth")
    public ClientConfigurationData pulsarClientConfig() throws MalformedURLException {
        var data = new ClientConfigurationData();
        data.setAuthentication(AuthenticationFactoryOAuth2.clientCredentials(new URL(issuerUrl), PulsarAuth.class.getResource(credentials), audience));
        return data;
    }
}

This assumes that the key file is included to the application classpath as a resource, then the configuration would like the following:

mp.messaging.incoming.prices.client-configuration=pulsar-auth

pulsar.tenant=public
pulsar.namespace=default
pulsar.client.serviceUrl=pulsar+ssl://quarkus-71eaadbf-a6f3-4355-85d2-faf436b23d86.aws-euc1-prod-snci-pool-slug.streamnative.aws.snio.cloud:6651
pulsar.issuerUrl=https://auth.streamnative.cloud/
pulsar.audience=urn:sn:pulsar:o-rfwel:redhat
pulsar.credentials=/o-rfwel-quarkus-app.json

Note that channels using the client configuration identified with pulsar-auth need to set the client-configuration attribute.

9. Health Checks

The Quarkus extension reports startup, readiness and liveness of each channel managed by the Pulsar connector. Health checks rely on the Pulsar client to verify that a connection is established with the broker.

Startup and Readiness probes for both inbound and outbound channels report OK when the connection with the broker is established.

The Liveness probe for both inbound and outbound channels reports OK when the connection is established with the broker AND that no failures have been caught.

Note that a message processing failures nacks the message which is then handled by the failure-strategy. It is the responsibility of the failure-strategy to report the failure and influence the outcome of the liveness checks. The fail failure strategy reports the failure and so the liveness check will report the failure.

10. Configuration Reference

Following are the list of configuration attributes for the Pulsar connector channels, consumers, producers and clients. See the Pulsar Client Configuration for more information on how the Pulsar clients are configured.

10.1. Incoming channel configuration (receiving from Pulsar)

The following attributes are configured using:

mp.messaging.incoming.your-channel-name.attribute=value

{includes}/smallrye-pulsar-incoming.adoc

You can also configure properties supported by the underlying Pulsar consumer.

These properties can also be globally configured using pulsar.consumer prefix:

pulsar.consumer.subscriptionInitialPosition=Earliest

{includes}/smallrye-pulsar-consumer.adoc

10.2. Outgoing channel configuration (publishing to Pulsar)

{includes}/smallrye-pulsar-outgoing.adoc

You can also configure properties supported by the underlying Pulsar producer.

These properties can also be globally configured using pulsar.producer prefix:

pulsar.producer.batchingEnabled=false

{includes}/smallrye-pulsar-producer.adoc

10.3. Pulsar Client Configuration

Following is the configuration reference for the underlying PulsarClient. These options can be configured using the channel attribute:

mp.messaging.incoming.your-channel-name.numIoThreads=4

Or configured globally using pulsar.client prefix:

pulsar.client.serviceUrl=pulsar://pulsar:6650

{includes}/smallrye-pulsar-client.adoc

Important

Configuration properties not configurable in configuration files (non-serializable) is noted in the column Config file.

11. Going further

This guide has shown how you can interact with Pulsar using Quarkus. It utilizes Quarkus Messaging to build data streaming applications.

If you want to go further, check the documentation of SmallRye Reactive Messaging, the implementation used in Quarkus.

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Apache Pulsar Reference Guide

1. Introduction

2. Quarkus Extension for Apache Pulsar

3. Configuring SmallRye Pulsar Connector

4. Receiving messages from Pulsar

4.1. Example

4.2. Blocking processing

4.3. Pulsar Subscription Types

4.4. Deserialization and Pulsar Schema

4.5. Acknowledgement Strategies

4.6. Failure Handling Strategies

4.6.1. Acknowledgement timeout

4.6.2. Reconsume later and retry letter topic

4.6.3. Dead-letter topic

4.7. Receiving Pulsar Messages in Batches

5. Sending messages to Pulsar

5.1. Example

5.2. Serialization and Pulsar Schema

5.3. Sending key/value pairs

5.4. Acknowledgement

5.5. Back-pressure and inflight records

5.6. Producer Batching

6. Pulsar Transactions and Exactly-Once Processing

6.1. Exactly-Once Processing

7. Pulsar Schema Configuration & Auto Schema Discovery

7.1. Auto Schema Discovery

8. Configuring Pulsar clients

8.1. Configuring Pulsar Authentication

8.1.1. Configuring authentication to Pulsar using mTLS

8.1.2. Configuring access to Datastax Luna Streaming

8.1.3. Configuring access to StreamNative Cloud

9. Health Checks

10. Configuration Reference

10.1. Incoming channel configuration (receiving from Pulsar)

10.2. Outgoing channel configuration (publishing to Pulsar)

10.3. Pulsar Client Configuration

11. Going further

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Apache Pulsar Reference Guide

1. Introduction

2. Quarkus Extension for Apache Pulsar

3. Configuring SmallRye Pulsar Connector

4. Receiving messages from Pulsar

4.1. Example

4.2. Blocking processing

4.3. Pulsar Subscription Types

4.4. Deserialization and Pulsar Schema

4.5. Acknowledgement Strategies

4.6. Failure Handling Strategies

4.6.1. Acknowledgement timeout

4.6.2. Reconsume later and retry letter topic

4.6.3. Dead-letter topic

4.7. Receiving Pulsar Messages in Batches

5. Sending messages to Pulsar

5.1. Example

5.2. Serialization and Pulsar Schema

5.3. Sending key/value pairs

5.4. Acknowledgement

5.5. Back-pressure and inflight records

5.6. Producer Batching

6. Pulsar Transactions and Exactly-Once Processing

6.1. Exactly-Once Processing

7. Pulsar Schema Configuration & Auto Schema Discovery

7.1. Auto Schema Discovery

8. Configuring Pulsar clients

8.1. Configuring Pulsar Authentication

8.1.1. Configuring authentication to Pulsar using mTLS

8.1.2. Configuring access to Datastax Luna Streaming

8.1.3. Configuring access to StreamNative Cloud

9. Health Checks

10. Configuration Reference

10.1. Incoming channel configuration (receiving from Pulsar)

10.2. Outgoing channel configuration (publishing to Pulsar)

10.3. Pulsar Client Configuration

11. Going further