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Container Source Example
ContainerSource will start a container image which will generate events under certain situations and send messages to a sink URI. It also can be an easy way to support your own event sources in Knative. This guide shows how to configure ContainerSource as an event source for functions and summarizes guidelines for creating your own event source as a ContainerSource.
Create a heartbeats ContainerSource
Prerequisites
- Setup Knative Serving.
- Setup Knative Eventing and Sources.
Prepare the heartbeats image
Knative event-sources has a sample of heartbeats event source. You could clone the source code by
git clone -b "{{< branch >}}" https://github.com/knative/eventing-contrib.git
And then build a heartbeats image and publish to your image repo with
ko publish knative.dev/eventing-contrib/cmd/heartbeats
Note: ko publish
requires:
KO_DOCKER_REPO
to be set. (e.g.gcr.io/[gcloud-project]
ordocker.io/<username>
)- you to be authenticated with your
KO_DOCKER_REPO
docker
to be installed
Create a Knative Service
In order to verify ContainerSource
is working, we will create a Event Display
Service that dumps incoming messages to its log.
apiVersion: serving.knative.dev/v1
kind: Service
metadata:
name: event-display
spec:
template:
spec:
containers:
- image: gcr.io/knative-releases/knative.dev/eventing-contrib/cmd/event_display
Use following command to create the service from service.yaml
:
kubectl apply --filename service.yaml
The status of the created service can be seen using:
kubectl get ksvc
NAME URL LATESTCREATED LATESTREADY READY REASON
event-display http://event-display.default.1.2.3.4.xip.io event-display-gqjbw event-display-gqjbw True
Create a ContainerSource using the heartbeats image
In order to run the heartbeats container as an event source, you have to create
a concrete ContainerSource with specific arguments and environment settings. Be
sure to replace heartbeats_image_uri
with a valid uri for your heartbeats
image in your image repo in heartbeats-source.yaml
file. Note that arguments and environment variables are set and will be passed
to the container.
apiVersion: sources.knative.dev/v1
kind: ContainerSource
metadata:
name: test-heartbeats
spec:
template:
spec:
containers:
- image: <heartbeats_image_uri>
name: heartbeats
args:
- --period=1
env:
- name: POD_NAME
value: "mypod"
- name: POD_NAMESPACE
value: "event-test"
sink:
ref:
apiVersion: serving.knative.dev/v1
kind: Service
name: event-display
Use the following command to create the event source from
heartbeats-source.yaml
:
kubectl apply --filename heartbeats-source.yaml
Verify
We will verify that the message was sent to the Knative eventing system by looking at event-display service logs.
kubectl logs -l serving.knative.dev/service=event-display -c user-container --since=10m
You should see log lines showing the request headers and body of the event message sent by the heartbeats source to the display function:
☁️ cloudevents.Event
Validation: valid
Context Attributes,
specversion: 1.0
type: dev.knative.eventing.samples.heartbeat
source: https://knative.dev/eventing-contrib/cmd/heartbeats/#event-test/mypod
id: 2b72d7bf-c38f-4a98-a433-608fbcdd2596
time: 2019-10-18T15:23:20.809775386Z
contenttype: application/json
Extensions,
beats: true
heart: yes
the: 42
Data,
{
"id": 2,
"label": ""
}
Create a new event source using ContainerSource
In order to create a new event source using ContainerSource, you will create a container image at first, and then create a ContainerSource with the image uri and specify the values of parameters.
Develop, build and publish a container image
The container image can be developed with any language, build and publish with any tools you like. Here are some basic guidelines:
- The container image must have a
main
method to start with. - The
main
method will accept parameters from arguments and environment variables. - Two environments variables will be injected by the
ContainerSource
controller,K_SINK
andK_CE_OVERRIDES
, resolved fromspec.sink
andspec.ceOverrides
respectively. - The event messages shall be sent to the sink URI specified in
K_SINK
. The message can be any format. CloudEvents format is recommended.
heartbeats event source is a sample for your reference.
Create the ContainerSource using this container image
When the container image is ready, a YAML file will be used to create a concrete
ContainerSource
. Use heartbeats-source.yaml as a
sample for reference. Learn more about the ContainerSource
specification.
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