in-memory-channel

In-Memory Channels

In-memory channels are a best effort Channel. They should NOT be used in Production. They are useful for development.

They differ from most Channels in that they have:

• No persistence.
  • If a Pod goes down, messages go with it.
• No ordering guarantee.
  • There is nothing enforcing an ordering, so two messages that arrive at the same time may go downstream in any order.
  • Different downstream subscribers may see different orders.
• No redelivery attempts.
  • If downstream rejects a request, a log message is written, but that request is never sent again.

Deployment steps:

1. Setup Knative Eventing.

2. Apply the 'in-memory-channel' ClusterChannelProvisioner, Controller, and Dispatcher.

   ko apply -f config/provisioners/in-memory-channel/in-memory-channel.yaml

3. Create Channels that reference the 'in-memory-channel'.

   apiVersion: eventing.knative.dev/v1alpha1
   kind: Channel
   metadata:
     name: foo
   spec:
     provisioner:
       apiVersion: eventing.knative.dev/v1alpha1
       kind: ClusterChannelProvisioner
       name: in-memory-channel

Components

The major components are:

• ClusterChannelProvisioner Controller
• Channel Controller
• Channel Dispatcher
• Channel Dispatcher Config Map.

The ClusterChannelProvisioner Controller and the Channel Controller are colocated in one Pod.

kubectl get deployment -n knative-eventing in-memory-channel-controller

The Channel Dispatcher receives and distributes all events. There is a single Dispatcher for all in-memory Channels.

kubectl get deployment -n knative-eventing in-memory-channel-dispatcher

The Channel Dispatcher Config Map is used to send information about Channels and Subscriptions from the Channel Controller to the Channel Dispatcher.

kubectl get configmap -n knative-eventing in-memory-channel-dispatcher-config-map