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Getting Started with Eventing
Use this guide to learn how to create, send, and verify events in Knative. The steps in this guide demonstrate a basic developer flow for managing events in Knative, including:
Before you begin
To complete this guide, you will need the following installed and running:
-
A Kubernetes cluster running v1.15 or higher.
-
kubectl
CLI tool within a minor version of your Kubernetes cluster. -
Knative Eventing component.
- Knative Eventing in-memory channel.
Important Note: Some Knative Eventing features do not work when using Minikube due to this bug. For local testing you can use kind.
Installing Knative Eventing
If you previously created a Knative cluster, you might already have Knative Eventing installed and running. You can check to see if the Eventing component exists on your cluster by running:
kubectl get pods --namespace knative-eventing
If the knative-eventing
namespace or the imc-controller-*
does not exist, use the following steps to install Knative Eventing with the in-memory channel:
-
Make sure that you have a functioning Kubernetes cluster. See the Comprehensive Install guide for more information.
-
Old versions of Knative Serving doesn't necessarily work well with latest Knative Eventing, so try to install the latest version of Knative Serving.
-
If your Kubernetes cluster comes with pre-installed Istio, make sure it has
cluster-local-gateway
deployed. Depending on which Istio version you have, you'd need to apply theistio-knative-extras.yaml
in the corresponding version folder at here.
-
-
Install the Eventing CRDs by running the following command:
kubectl apply --selector knative.dev/crd-install=true \ --filename https://github.com/knative/eventing/releases/download/v0.14.0/eventing.yaml
-
Finish installing Eventing resources by running the following command:
kubectl apply --filename https://github.com/knative/eventing/releases/download/v0.14.0/eventing.yaml
Installing the CRDs first can prevent race conditions, which might cause failures during the install. Race conditions exist during install because a CRD must be defined before an instance of that resource can be created. Defining all CRDs before continuing with the rest of the installation prevents this problem.
-
Confirm that Knative Eventing is correctly installed by running the following command:
kubectl get pods --namespace knative-eventing
This will return the following result:
NAME READY STATUS RESTARTS AGE eventing-controller-6cdf6ff785-44k98 1/1 Running 0 29m eventing-webhook-6c4f6699d8-qclbx 1/1 Running 0 29m imc-controller-85cdb4946b-h2msj 1/1 Running 0 13m imc-dispatcher-5f4689d868-fspt6 1/1 Running 0 13m sources-controller-5847564f4f-z59xc 1/1 Running 0 29m
Setting up Knative Eventing Resources
Before you start to manage events, you need to create the objects needed to transport the events.
Creating and configuring an Eventing namespace
In this section you create the event-example
namespace and then add the knative-eventing-injection
label to that namespace. You use namespaces to group together and organize your Knative resources, including the Eventing subcomponents.
-
Run the following command to create a namespace called
event-example
:kubectl create namespace event-example
This creates an empty namespace called
event-example
. -
Add a label to your namespace with the following command:
kubectl label namespace event-example knative-eventing-injection=enabled
This gives the
event-example
namespace theknative-eventing-injection
label, which adds resources that will allow you to manage your events.
In the next section, you will need to verify that the resources you added in this section are running correctly. Then, you can create the rest of the eventing resources you need to manage events.
Validating that the Broker
is running
The Broker
ensures that every event sent by event producers arrives at the correct event consumers. The Broker
was created when you labeled your namespace as ready for eventing, but it is important to verify that your Broker
is working correctly. In this guide, you will use the default broker.
-
Run the following command to verify that the
Broker
is in a healthy state:kubectl --namespace event-example get Broker default
This shows the
Broker
that you created:NAME READY REASON URL AGE default True http://default-broker.event-example.svc.cluster.local 1m
When the
Broker
has theREADY=True
state, it can begin to manage any events it receives. -
If
READY=False
, wait 2 minutes and re-run the command. If you continue to receive theREADY=False
, see the Debugging Guide to help troubleshoot the issue.
Now that your Broker
is ready to manage events, you can create and configure your event producers and consumers.
Creating event consumers
Your event consumers receive the events sent by event producers. In this step, you will create two event consumers, hello-display
and goodbye-display
, to demonstrate how you can configure your event producers to selectively target a specific consumer.
-
To deploy the
hello-display
consumer to your cluster, run the following command:kubectl --namespace event-example apply --filename - << END apiVersion: apps/v1 kind: Deployment metadata: name: hello-display spec: replicas: 1 selector: matchLabels: &labels app: hello-display template: metadata: labels: *labels spec: containers: - name: event-display # Source code: https://github.com/knative/eventing-contrib/tree/master/cmd/event_display image: gcr.io/knative-releases/knative.dev/eventing-contrib/cmd/event_display --- # Service pointing at the previous Deployment. This will be the target for event # consumption. kind: Service apiVersion: v1 metadata: name: hello-display spec: selector: app: hello-display ports: - protocol: TCP port: 80 targetPort: 8080 END
-
To deploy the
goodbye-display
consumer to your cluster, run the following command:kubectl --namespace event-example apply --filename - << END apiVersion: apps/v1 kind: Deployment metadata: name: goodbye-display spec: replicas: 1 selector: matchLabels: &labels app: goodbye-display template: metadata: labels: *labels spec: containers: - name: event-display # Source code: https://github.com/knative/eventing-contrib/tree/master/cmd/event_display image: gcr.io/knative-releases/knative.dev/eventing-contrib/cmd/event_display --- # Service pointing at the previous Deployment. This will be the target for event # consumption. kind: Service apiVersion: v1 metadata: name: goodbye-display spec: selector: app: goodbye-display ports: - protocol: TCP port: 80 targetPort: 8080 END
-
Just like you did with the
Broker
, verify that your event consumers are working by running the following command:kubectl --namespace event-example get deployments hello-display goodbye-display
This lists the
hello-display
andgoodbye-display
consumers that you deployed:NAME DESIRED CURRENT UP-TO-DATE AVAILABLE AGE hello-display 1 1 1 1 26s NAME DESIRED CURRENT UP-TO-DATE AVAILABLE AGE goodbye-display 1 1 1 1 16s
The number of replicas in your DESIRED column should match the number of replicas in your AVAILABLE column, which might take a few minutes. If after two minutes the numbers do not match, then see the Debugging Guide to help troubleshoot the issue.
Creating Triggers
A Trigger defines the events that you want each of your event consumers
to receive. Your Broker
uses triggers to forward events to the right consumers. Each trigger can specify a filter to select relevant events based on the Cloud Event context attributes.
-
To create the first
Trigger
, run the following command:kubectl --namespace event-example apply --filename - << END apiVersion: eventing.knative.dev/v1alpha1 kind: Trigger metadata: name: hello-display spec: filter: attributes: type: greeting subscriber: ref: apiVersion: v1 kind: Service name: hello-display END
The command creates a trigger that sends all events of type
greeting
to your event consumer namedhello-display
. -
To add the second
Trigger
, run the following command:kubectl --namespace event-example apply --filename - << END apiVersion: eventing.knative.dev/v1alpha1 kind: Trigger metadata: name: goodbye-display spec: filter: attributes: source: sendoff subscriber: ref: apiVersion: v1 kind: Service name: goodbye-display END
The command creates a trigger that sends all events of source
sendoff
to your event consumer namedgoodbye-display
. -
Verify that the triggers are working correctly by running the following command:
kubectl --namespace event-example get triggers
This returns the
hello-display
andgoodbye-display
triggers that you created:NAME READY REASON BROKER SUBSCRIBER_URI AGE goodbye-display True default http://goodbye-display.event-example.svc.cluster.local/ 9s hello-display True default http://hello-display.event-example.svc.cluster.local/ 16s
If the triggers are correctly configured, they will be ready and pointing to the correct Broker (the default broker) and SUBSCRIBER_URI (triggerName.namespaceName.svc.cluster.local). If this is not the case, see the Debugging Guide to help troubleshoot the issue.
You have now created all of the resources needed to receive and manage events. You created the Broker
, which manages the events sent to event consumers with the help of triggers. In the next section, you will make the event producer that will be used to create your events.
Creating event producers
In this section you will create an event producer that you can use to interact with the Knative Eventing subcomponents you created earlier. Most events are created systematically, but this guide uses curl
to manually send individual events and demonstrate how these events are received by the correct event consumer. Because you can only access the Broker
from within your Eventing cluster, you must create a Pod
within that cluster to act as your event producer.
In the following step, you will create a Pod
that executes your curl
commands to send events to the Broker
in your Eventing cluster.
To create the Pod
, run the following command:
kubectl --namespace event-example apply --filename - << END
apiVersion: v1
kind: Pod
metadata:
labels:
run: curl
name: curl
spec:
containers:
# This could be any image that we can SSH into and has curl.
- image: radial/busyboxplus:curl
imagePullPolicy: IfNotPresent
name: curl
resources: {}
stdin: true
terminationMessagePath: /dev/termination-log
terminationMessagePolicy: File
tty: true
END
Now that you've set up your Eventing cluster to send and consume events, you will use HTTP requests to manually send separate events and demonstrate how each of those events can target your individual event consumers in the next section.
Sending Events to the Broker
Now that you've created the Pod, you can create an event by sending an HTTP request to the Broker
. SSH into the Pod
by running the following command:
kubectl --namespace event-example attach curl -it
You have sshed into the Pod, and can now make a HTTP request. A prompt similar to the one below will appear:
Defaulting container name to curl.
Use 'kubectl describe pod/ -n event-example' to see all of the containers in this pod.
If you don't see a command prompt, try pressing enter.
[ root@curl:/ ]$
To show the various types of events you can send, you will make three requests:
-
To make the first request, which creates an event that has the
type
greeting
, run the following in the SSH terminal:curl -v "http://default-broker.event-example.svc.cluster.local" \ -X POST \ -H "Ce-Id: say-hello" \ -H "Ce-Specversion: 0.3" \ -H "Ce-Type: greeting" \ -H "Ce-Source: not-sendoff" \ -H "Content-Type: application/json" \ -d '{"msg":"Hello Knative!"}'
When the
Broker
receives your event,hello-display
will activate and send it to the event consumer of the same name.If the event has been received, you will receive a
202 Accepted
response similar to the one below:< HTTP/1.1 202 Accepted < Content-Length: 0 < Date: Mon, 12 Aug 2019 19:48:18 GMT
-
To make the second request, which creates an event that has the
source
sendoff
, run the following in the SSH terminal:curl -v "http://default-broker.event-example.svc.cluster.local" \ -X POST \ -H "Ce-Id: say-goodbye" \ -H "Ce-Specversion: 0.3" \ -H "Ce-Type: not-greeting" \ -H "Ce-Source: sendoff" \ -H "Content-Type: application/json" \ -d '{"msg":"Goodbye Knative!"}'
When the
Broker
receives your event,goodbye-display
will activate and send the event to the event consumer of the same name.If the event has been received, you will receive a
202 Accepted
response similar to the one below:< HTTP/1.1 202 Accepted < Content-Length: 0 < Date: Mon, 12 Aug 2019 19:48:18 GMT
-
To make the third request, which creates an event that has the
type
greeting
and thesource
sendoff
, run the following in the SSH terminal:curl -v "http://default-broker.event-example.svc.cluster.local" \ -X POST \ -H "Ce-Id: say-hello-goodbye" \ -H "Ce-Specversion: 0.3" \ -H "Ce-Type: greeting" \ -H "Ce-Source: sendoff" \ -H "Content-Type: application/json" \ -d '{"msg":"Hello Knative! Goodbye Knative!"}'
When the
Broker
receives your event,hello-display
andgoodbye-display
will activate and send the event to the event consumer of the same name.If the event has been received, you will receive a
202 Accepted
response similar to the one below:< HTTP/1.1 202 Accepted < Content-Length: 0 < Date: Mon, 12 Aug 2019 19:48:18 GMT
-
Exit SSH by typing
exit
into the command prompt.
You have sent two events to the hello-display
event consumer and two events to the goodbye-display
event consumer (note that say-hello-goodbye
activates the trigger conditions for both hello-display
and goodbye-display
). You will verify that these events were received correctly in the next section.
Verifying events were received
After sending events, verify that your events were received by the appropriate Subscribers
.
-
Look at the logs for the
hello-display
event consumer by running the following command:kubectl --namespace event-example logs -l app=hello-display --tail=100
This returns the
Attributes
andData
of the events you sent tohello-display
:☁️ cloudevents.Event Validation: valid Context Attributes, specversion: 0.3 type: greeting source: not-sendoff id: say-hello time: 2019-05-20T17:59:43.81718488Z contenttype: application/json Extensions, knativehistory: default-broker-srk54-channel-24gls.event-example.svc.cluster.local Data, { "msg": "Hello Knative!" } ☁️ cloudevents.Event Validation: valid Context Attributes, specversion: 0.3 type: greeting source: sendoff id: say-hello-goodbye time: 2019-05-20T17:59:54.211866425Z contenttype: application/json Extensions, knativehistory: default-broker-srk54-channel-24gls.event-example.svc.cluster.local Data, { "msg": "Hello Knative! Goodbye Knative!" }
-
Look at the logs for the
goodbye-display
event consumer by running the following command:kubectl --namespace event-example logs -l app=goodbye-display --tail=100
This returns the
Attributes
andData
of the events you sent togoodbye-display
:☁️ cloudevents.Event Validation: valid Context Attributes, specversion: 0.3 type: not-greeting source: sendoff id: say-goodbye time: 2019-05-20T17:59:49.044926148Z contenttype: application/json Extensions, knativehistory: default-broker-srk54-channel-24gls.event-example.svc.cluster.local Data, { "msg": "Goodbye Knative!" } ☁️ cloudevents.Event Validation: valid Context Attributes, specversion: 0.3 type: greeting source: sendoff id: say-hello-goodbye time: 2019-05-20T17:59:54.211866425Z contenttype: application/json Extensions, knativehistory: default-broker-srk54-channel-24gls.event-example.svc.cluster.local Data, { "msg": "Hello Knative! Goodbye Knative!" }
Cleaning up
After you finish this guide, delete your namespace to conserve resources if you do not plan to use them.
Note: If you plan to continue learning about Knative Eventing with one of our code samples, check the requirements of the sample and make sure you do not need a namespace before you delete event-example
. You can always reuse your namespaces.
Run the following command to delete event-example
:
kubectl delete namespace event-example
This removes the namespace and all of its resources from your cluster.
What’s next
You've learned the basics of the Knative Eventing workflow. Here are some additional resources to help you continue to build with the Knative Eventing component.
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