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Sequence terminal
We are going to create the following logical configuration. We create a
PingSource, feeding events to a Sequence
.
Sequence can then do either external work, or out of band create additional
events.
The functions used in these examples live in https://github.com/knative/eventing-contrib/blob/master/cmd/appender/main.go.
Prerequisites
For this example, we’ll assume you have set up an InMemoryChannel
as well as
Knative Serving (for our functions). The examples use default
namespace,
again, if you want to deploy to another Namespace, you will need to modify the
examples to reflect this.
If you want to use different type of Channel
, you will have to modify the
Sequence.Spec.ChannelTemplate
to create the appropriate Channel resources.
Setup
Create the Knative Services
First create the 3 steps that will be referenced in the Steps.
apiVersion: serving.knative.dev/v1
kind: Service
metadata:
name: first
spec:
template:
spec:
containers:
- image: gcr.io/knative-releases/knative.dev/eventing-contrib/cmd/appender
env:
- name: MESSAGE
value: " - Handled by 0"
---
apiVersion: serving.knative.dev/v1
kind: Service
metadata:
name: second
spec:
template:
spec:
containers:
- image: gcr.io/knative-releases/knative.dev/eventing-contrib/cmd/appender
env:
- name: MESSAGE
value: " - Handled by 1"
---
apiVersion: serving.knative.dev/v1
kind: Service
metadata:
name: third
spec:
template:
spec:
containers:
- image: gcr.io/knative-releases/knative.dev/eventing-contrib/cmd/appender
env:
- name: MESSAGE
value: " - Handled by 2"
---
kubectl -n default create -f ./steps.yaml
Create the Sequence
The sequence.yaml
file contains the specifications for creating the Sequence.
If you are using a different type of Channel, you need to change the
spec.channelTemplate to point to your desired Channel.
apiVersion: flows.knative.dev/v1
kind: Sequence
metadata:
name: sequence
spec:
channelTemplate:
apiVersion: messaging.knative.dev/v1
kind: InMemoryChannel
steps:
- ref:
apiVersion: serving.knative.dev/v1
kind: Service
name: first
- ref:
apiVersion: serving.knative.dev/v1
kind: Service
name: second
- ref:
apiVersion: serving.knative.dev/v1
kind: Service
name: third
Change default
below to create the Sequence
in the Namespace where you want
the resources to be created.
Here, if you are using different type of Channel, you need to change the spec.channelTemplate to point to your desired Channel.
kubectl -n default create -f ./sequence.yaml
Create the PingSource targeting the Sequence
This will create a PingSource which will send a CloudEvent with
{"message": "Hello world!"}
as the data payload every 2 minutes.
apiVersion: sources.knative.dev/v1beta2
kind: PingSource
metadata:
name: ping-source
spec:
schedule: "*/2 * * * *"
contentType: "application/json"
data: '{"message": "Hello world!"}'
sink:
ref:
apiVersion: flows.knative.dev/v1
kind: Sequence
name: sequence
kubectl -n default create -f ./ping-source.yaml
Inspecting the results
You can now see the final output by inspecting the logs of the event-display
pods. Note that since we set the PingSource
to emit every 2 minutes, it might
take some time for the events to show up in the logs.
kubectl -n default get pods
Let’s look at the logs for the first Step
in the Sequence
:
kubectl -n default logs -l serving.knative.dev/service=first -c user-container --tail=-1
2020/03/02 21:28:00 listening on 8080, appending " - Handled by 0" to events
2020/03/02 21:28:01 Received a new event:
2020/03/02 21:28:01 [2020-03-02T21:28:00.0010247Z] /apis/v1/namespaces/default/pingsources/ping-source dev.knative.sources.ping: &{Sequence:0 Message:Hello world!}
2020/03/02 21:28:01 Transform the event to:
2020/03/02 21:28:01 [2020-03-02T21:28:00.0010247Z] /apis/v1/namespaces/default/pingsources/ping-source dev.knative.sources.ping: &{Sequence:0 Message:Hello world! - Handled by 0}
And you can see that the initial PingSource message ("Hello World!")
has now
been modified by the first step in the Sequence to include " - Handled by 0”.
Exciting :)
Then we can look at the output of the second Step in the Sequence
:
kubectl -n default logs -l serving.knative.dev/service=second -c user-container --tail=-1
2020/03/02 21:28:02 listening on 8080, appending " - Handled by 1" to events
2020/03/02 21:28:02 Received a new event:
2020/03/02 21:28:02 [2020-03-02T21:28:00.0010247Z] /apis/v1/namespaces/default/pingsources/ping-source dev.knative.sources.ping: &{Sequence:0 Message:Hello world! - Handled by 0}
2020/03/02 21:28:02 Transform the event to:
2020/03/02 21:28:02 [2020-03-02T21:28:00.0010247Z] /apis/v1/namespaces/default/pingsources/ping-source dev.knative.sources.ping: &{Sequence:0 Message:Hello world! - Handled by 0 - Handled by 1}
And as expected it’s now been handled by both the first and second Step as reflected by the Message being now: “Hello world! - Handled by 0 - Handled by 1”
Then we can look at the output of the last Step in the Sequence
:
kubectl -n default logs -l serving.knative.dev/service=third -c user-container --tail=-1
2020/03/02 21:28:03 listening on 8080, appending " - Handled by 2" to events
2020/03/02 21:28:03 Received a new event:
2020/03/02 21:28:03 [2020-03-02T21:28:00.0010247Z] /apis/v1/namespaces/default/pingsources/ping-source dev.knative.sources.ping: &{Sequence:0 Message:Hello world! - Handled by 0 - Handled by 1}
2020/03/02 21:28:03 Transform the event to:
2020/03/02 21:28:03 [2020-03-02T21:28:00.0010247Z] /apis/v1/namespaces/default/pingsources/ping-source dev.knative.sources.ping: &{Sequence:0 Message:Hello world! - Handled by 0 - Handled by 1 - Handled by 2}
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