NATS Streaming Channels

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.

Deployment steps

1. Setup Knative Eventing.

2. If not done already, install a JetStream Broker

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

Components

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.