JetStream channels are alpha-quality Channels that are backed by JetStream.

They offer:

• Persistence
  • If the Channel's Pod goes down, all events already ACKed by the Channel will persist and be retransmitted when the Pod restarts.
• Redelivery attempts
  • If downstream rejects an event, that request is attempted again. NOTE: downstream must successfully process the event within one minute or the delivery is assumed to have failed and will be reattempted.

They do not offer:

• Ordering guarantees
  • Events seen downstream may not occur in the same order they were inserted into the Channel.

1. Setup Knative Eventing.

2. If not done already, install NATS JetStream

3. Apply the NATSS configuration (from project root):

   ko apply -f ./config

4. Create JetStream channels:

    apiVersion: messaging.knative.dev/v1alpha1
    kind: NatsJetStreamChannel
    metadata:
        name: channel-defaults
        namespace: knative-eventing

The major components are:

• JetStream
• JetStream Channel Controller
• JetStream Channel Dispatcher

The JetStream Channel Controller is located in one Pod.

kubectl get deployment -n knative-eventing jetstream-ch-controller

The JetStream Channel Dispatcher receives and distributes all events. There is a single Dispatcher for all JetStream Channels.

By default the components are configured to connect to NATS at nats://nats.nats-io.svc.cluster.local:4222.