channel

README

In-Memory Channels

In-memory channels are a best effort channel. They have the following characteristics:

• No Persistence.
  • When 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 to subscribers in any order.
  • Different downstream subscribers may see different orders.
• No Redelivery Attempts.
  • When a subscriber rejects a message, there is no attempts to retry sending it.
• Dead Letter Sink.
  • When a subscriber rejects a message, this message is sent to the dead letter sink, if present, otherwise it is dropped.

Deployment steps:

1. Setup Knative Eventing.

2. Apply the InMemoryChannel CRD, Controller, and cluster-scoped Dispatcher.

   ko apply -f config/channels/in-memory-channel/
   

3. Create InMemoryChannels

   kubectl apply --filename - << END
   apiVersion: messaging.knative.dev/v1beta1
   kind: InMemoryChannel
   metadata:
     name: foo
   END
   

Components

The major components are:

• InMemoryChannel Controller
• InMemoryChannel Dispatcher

kubectl get deployment -n knative-eventing imc-controller

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

kubectl get deployment -n knative-eventing imc-dispatcher

Namespace Dispatchers

By default events are received and dispatched by a single cluster-scoped dispatcher components. You can also specify whether events should be received and dispatched by the dispatcher in the same namespace as the channel definition by adding the eventing.knative.dev/scope: namespace annotation. For instance:

kubectl apply --filename - << END
apiVersion: messaging.knative.dev/v1beta1
kind: InMemoryChannel
metadata:
  name: foo-ns
  namespace: default
  annotations:
    eventing.knative.dev/scope: namespace
END

Documentation

Overview

Package channel is a placeholder that allows us to pull in config files via go mod vendor.