Add Prometheus metrics exporter

docs/configuration.md

@@ -5,7 +5,7 @@ YAML's format, like Python code, is whitespace dependent for control structure i
 blocks. If you're having problems with your rejected configuration, the first
 thing you should do is ensure that the YAML syntax is correct.
 
-The configuration file is split into three main sections: `Application`, `Daemon`, and `Logging`.
+The configuration file is split into two main sections: `Application` and `Logging`.
 
 ## Application
 
@@ -15,7 +15,7 @@ The application section of the configuration is broken down into multiple top-le
 |--------|-------------|
 | `poll_interval` | How often rejected should poll consumer processes for status in seconds (int/float) |
 | `sentry_dsn` | If Sentry support is installed, optionally set a global DSN for all consumers (str) |
-| `stats` | Enable and configure statsd metric submission (obj) |
+| `stats` | Enable and configure metrics submission via statsd and/or Prometheus (obj) |
 | `Connections` | A subsection with RabbitMQ connection information for consumers (obj) |
 | `Consumers` | Where each consumer type is configured (obj) |
 
@@ -24,19 +24,19 @@ The application section of the configuration is broken down into multiple top-le
 | Option | Description |
 |--------|-------------|
 | `log` | Toggle top-level logging of consumer process stats (bool) |
-| `influxdb` | Configure the submission of per-message measurements to InfluxDB (obj) |
+| `prometheus` | Configure the Prometheus metrics exporter (obj) |
 | `statsd` | Configure the submission of per-message measurements to statsd (obj) |
 
-#### influxdb
+#### prometheus
+
+Requires `rejected[prometheus]` to be installed.
 
 | Option | Description |
 |--------|-------------|
-| `scheme` | The scheme to use when submitting metrics to the InfluxDB server. Default: `http` (str) |
-| `host` | The hostname or ip address of the InfluxDB server. Default: `localhost` (str) |
-| `port` | The port of the influxdb server. Default: `8086` (int) |
-| `user` | An optional username to use when submitting measurements. (str) |
-| `password` | An optional password to use when submitting measurements. (str) |
-| `database` | The InfluxDB database to submit measurements to. Default: `rejected` (str) |
+| `enabled` | Toggle the Prometheus metrics HTTP endpoint on and off (bool) |
+| `port` | The port to serve the `/metrics` endpoint on. Default: `9090` (int) |
+
+See [Prometheus Metrics](#prometheus-metrics) below for the full list of exposed metrics.
 
 #### statsd
 
@@ -94,7 +94,7 @@ Each consumer entry should be a nested object with a unique name with consumer a
 | `message_type` | Used to validate the message type of a message before processing (str or list) |
 | `error_exchange` | The exchange to publish messages that raise `ProcessingException` to (str) |
 | `error_max_retry` | The number of `ProcessingException` raised on a message before dropping it (int) |
-| `influxdb_measurement` | When using InfluxDB, the measurement name for per-message measurements (str) |
+| `schema_uri_format` | Avro schema URI format with `{0}` placeholder for message type. Supports `file://` and `http(s)://` schemes. Requires `rejected[avro]` (str) |
 | `config` | Free-form key-value configuration section for the consumer (obj) |
 
 #### Consumer Connections
@@ -130,16 +130,6 @@ Structured connection options:
 | `consume` | Specify if the connection should consume on the connection (bool) |
 | `publisher_confirmation` | Enable publisher confirmations (bool) |
 
-## Daemon
-
-This section contains the settings required to run the application as a daemon:
-
-| Option | Description |
-|--------|-------------|
-| `user` | The username to run as when the process is daemonized (str) |
-| `group` | Optional group name to switch to when the process is daemonized (str) |
-| `pidfile` | The pidfile to write when the process is daemonized (str) |
-
 ## Logging
 
 Rejected uses `logging.config.dictConfig` to create a flexible method for
@@ -181,3 +171,59 @@ If your application is not logging anything, ensure that you have created a
 logger section in your configuration for your consumer package. For example, if
 your Consumer instance is named `myconsumer.MyConsumer`, make sure there is a
 `myconsumer` logger in the logging configuration.
+
+## Prometheus Metrics
+
+When `stats.prometheus.enabled` is `true` and `rejected[prometheus]` is installed,
+rejected exposes a `/metrics` HTTP endpoint on the configured port for Prometheus
+to scrape.
+
+### Built-in Counters
+
+All labeled by `consumer` name.
+
+| Metric | Description |
+|--------|-------------|
+| `rejected_messages_acked_total` | Messages acknowledged |
+| `rejected_messages_dropped_total` | Messages dropped |
+| `rejected_messages_failed_total` | Messages that resulted in errors |
+| `rejected_messages_nacked_total` | Messages negatively acknowledged |
+| `rejected_messages_processed_total` | Messages processed |
+| `rejected_messages_redelivered_total` | Redelivered messages |
+| `rejected_messages_requeued_total` | Messages requeued |
+| `rejected_processing_seconds_total` | Total processing time in seconds |
+| `rejected_exceptions_total` | Exceptions (labeled by `consumer` and `type`) |
+
+Exception `type` values: `consumer_exception`, `message_exception`,
+`processing_exception`, `unhandled_exception`.
+
+### Built-in Histograms
+
+All labeled by `consumer` name.
+
+| Metric | Description |
+|--------|-------------|
+| `rejected_processing_duration_seconds` | Per-message processing duration |
+| `rejected_message_age_seconds` | Age of messages at time of processing |
+
+### Built-in Gauges
+
+| Metric | Description |
+|--------|-------------|
+| `rejected_consumer_processes` | Number of active consumer processes |
+
+### Custom Metrics
+
+Metrics created via `Consumer.stats_add_duration`, `Consumer.stats_incr`, and
+`Consumer.stats_set_value` are automatically forwarded to Prometheus as
+dynamically created metrics:
+
+| Consumer Method | Prometheus Type | Metric Name Pattern |
+|----------------|----------------|---------------------|
+| `stats_add_duration(key, value)` | Histogram | `rejected_custom_{key}_seconds` |
+| `stats_track_duration(key)` | Histogram | `rejected_custom_{key}_seconds` |
+| `stats_incr(key, value)` | Counter | `rejected_custom_{key}_total` |
+| `stats_set_value(key, value)` | Gauge | `rejected_custom_{key}` |
+
+Metric names are sanitized: any characters not in `[a-zA-Z0-9_]` are replaced
+with underscores.

docs/index.md

@@ -13,7 +13,7 @@ data from the consumer processes and report on it.
 
 - Automatic exception handling including connection management and consumer restarting
 - Smart consumer classes that can automatically decode and deserialize message bodies based upon message headers
-- Metrics logging and submission to statsd and InfluxDB
+- Metrics via statsd and/or Prometheus
 - Built-in profiling of consumer code
 - Ability to write asynchronous code in consumers allowing for parallel communication with external resources
 
@@ -26,8 +26,11 @@ pip install rejected
 For optional features:
 
 ```bash
-pip install rejected[html]     # HTML message body support
-pip install rejected[msgpack]  # MessagePack support
+pip install rejected[avro]        # Avro datum serialization
+pip install rejected[html]        # HTML message body support
+pip install rejected[msgpack]     # MessagePack support
+pip install rejected[prometheus]  # Prometheus metrics exporter
+pip install rejected[sentry]      # Sentry error reporting
 ```
 
 ## Quick Start

example.yaml

@@ -5,6 +5,9 @@ Application:
   # sentry_dsn: https://[YOUR-SENTRY-DSN]
   stats:
     log: True
+    prometheus:
+      enabled: False
+      port: 9090
     statsd:
       enabled: False
       host: localhost

pyproject.toml

@@ -40,6 +40,7 @@ dependencies = [
 avro = ["fastavro>=1.7", "requests>=2.28"]
 html = ["beautifulsoup4"]
 msgpack = ["u-msgpack-python"]
+prometheus = ["prometheus-client>=0.20"]
 sentry = ["sentry-sdk>=2,<3"]
 
 [project.scripts]

rejected/config.py

@@ -43,8 +43,16 @@ class StatsdConfig(pydantic.BaseModel):
     include_hostname: bool = True
 
 
+class PrometheusConfig(pydantic.BaseModel):
+    enabled: bool = False
+    port: int = 9090
+
+
 class StatsConfig(pydantic.BaseModel):
     log: bool = False
+    prometheus: PrometheusConfig = pydantic.Field(
+        default_factory=PrometheusConfig
+    )
     statsd: StatsdConfig = pydantic.Field(default_factory=StatsdConfig)
 
 

rejected/mcp.py

@@ -14,7 +14,7 @@
 
 import psutil
 
-from . import __version__, process, state
+from . import __version__, process, prometheus, state
 
 LOGGER = logging.getLogger(__name__)
 
@@ -199,13 +199,24 @@ def collect_results(self, data_values):
         process_name = data_values['name']
         del data_values['name']
 
+        # Forward per-message observations to Prometheus
+        prometheus.observe(
+            consumer_name,
+            data_values.pop('durations', []),
+            data_values.pop('message_ages', []),
+            data_values.pop('custom_durations', {}),
+            data_values.pop('custom_counters', {}),
+            data_values.pop('custom_gauges', {}),
+        )
+
         # Add it to our last poll global data
         if consumer_name not in self.last_poll_results:
             self.last_poll_results[consumer_name] = {}
         self.last_poll_results[consumer_name][process_name] = data_values
 
         # Calculate the stats
         self.stats = self.calculate_stats(self.last_poll_results)
+        prometheus.update(self.stats)
 
     @staticmethod
     def consumer_keyword(counts):
@@ -225,9 +236,18 @@ def consumer_stats_counter():
 
         """
         return {
+            process.Process.ACKED: 0,
+            process.Process.CONSUMER_EXCEPTION: 0,
+            process.Process.DROPPED: 0,
             process.Process.ERROR: 0,
+            process.Process.MESSAGE_EXCEPTION: 0,
+            process.Process.NACKED: 0,
             process.Process.PROCESSED: 0,
+            process.Process.PROCESSING_EXCEPTION: 0,
             process.Process.REDELIVERED: 0,
+            process.Process.REQUEUED: 0,
+            process.Process.TIME_SPENT: 0,
+            process.Process.UNHANDLED_EXCEPTION: 0,
         }
 
     def get_consumer_process(self, consumer, name):
@@ -588,6 +608,9 @@ def run(self):
         self.set_state(self.STATE_ACTIVE)
         self.setup_consumers()
 
+        if self.config.stats.prometheus.enabled:
+            prometheus.start(self.config.stats.prometheus.port)
+
         # Set the SIGCHLD handler for child creation errors
         signal.signal(signal.SIGCHLD, self.on_sigchld)
 

rejected/process.py

@@ -486,6 +486,11 @@ def __init__(
         self.pending = collections.deque()
         self.prepend_path = None
         self.previous = None
+        self._duration_observations: list[float] = []
+        self._message_age_observations: list[float] = []
+        self._custom_durations: dict[str, list[float]] = {}
+        self._custom_counters: dict[str, int] = {}
+        self._custom_gauges: dict[str, float] = {}
         self.sentry_client = None
         self.state = self.STATE_INITIALIZING
         self._tasks: set[asyncio.Task] = set()
@@ -802,6 +807,7 @@ def on_processed(self, message, result, start_time):
         duration = time.monotonic() - start_time
         self.counters[self.TIME_SPENT] += duration
         self.measurement.add_duration(self.TIME_SPENT, duration)
+        self._duration_observations.append(duration)
 
         if result == data.MESSAGE_DROP:
             LOGGER.debug('Rejecting message due to drop return from consumer')
@@ -843,6 +849,11 @@ def on_processed(self, message, result, start_time):
 
         self.counters[self.PROCESSED] += 1
         self.measurement.set_tag(self.PROCESSED, True)
+        if message.properties.timestamp:
+            age = time.time() - message.properties.timestamp
+            if age > 0:
+                self._message_age_observations.append(age)
+        self._collect_custom_measurements()
         self.maybe_submit_measurement()
         self.reset_state()
 
@@ -943,6 +954,24 @@ def reject(self, message, requeue=True):
         self.measurement.set_tag(self.NACKED, True)
         self.measurement.set_tag(self.REQUEUED, requeue)
 
+    def _collect_custom_measurements(self):
+        """Accumulate per-message Measurement data for Prometheus."""
+        if not self.measurement:
+            return
+        # Custom durations (excluding processing_time, already tracked)
+        for key, values in self.measurement.durations.items():
+            if key == self.TIME_SPENT:
+                continue
+            self._custom_durations.setdefault(key, []).extend(values)
+        # Custom counters
+        for key, value in self.measurement.counters.items():
+            self._custom_counters[key] = (
+                self._custom_counters.get(key, 0) + value
+            )
+        # Custom gauges (values dict on Measurement)
+        for key, value in self.measurement.values.items():
+            self._custom_gauges[key] = value
+
     def report_stats(self):
         """Create the dict of stats data for the MCP stats queue"""
         if not self.previous:
@@ -954,8 +983,20 @@ def report_stats(self):
             'consumer_name': self.consumer_name,
             'counts': dict(self.counters),
             'previous': dict(self.previous),
+            'durations': list(self._duration_observations),
+            'message_ages': list(self._message_age_observations),
+            'custom_durations': {
+                k: list(v) for k, v in self._custom_durations.items()
+            },
+            'custom_counters': dict(self._custom_counters),
+            'custom_gauges': dict(self._custom_gauges),
         }
         self.previous = dict(self.counters)
+        self._duration_observations.clear()
+        self._message_age_observations.clear()
+        self._custom_durations.clear()
+        self._custom_counters.clear()
+        self._custom_gauges.clear()
         return values
 
     def reset_error_counter(self):