openshift-knative/showcase

A showcase for OpenShift Serverless

Knative Showcase

The apps in this repository are used to showcase basics of Knative Serving and Eventing. The same features are implemented both in Quarkus and Express.JS frameworks.

Features

The features below are there for two basic reasons. First reason is to showcase some of the features of the Knative (like scaling, traffic shaping, or event sending and receiving). The other group is to showcase some basic features almost every production ready application deployed on Kubernetes should have. The non-functional features were added, so the apps be close to the real world apps, and could serve as a reference for developers.

Knative related features

• Supports the PORT env

  PORT=3456
  # start the app... 
  http :$PORT

• /hello

  http :8080/hello

  Returns a hello JSON (sequenced), and sends Cloud Event to K_SINK target. A operational delay can be enforced by using DELAY (in msec) environmental variable.

• /events

  http :8080/events

  Returns a stream of Server-Sent Events, where each event is a CloudEvent represented in structured JSON format. This stream will continue to send next events if they come.

  kn event send --field a.b=true --to-url http://localhost:8080/events

  You can send events to the app, by POST /events endpoint. Those events will be stored in ephemeral im-memory storage and send to the listening clients.

Openshift Serverless related features

• / home page ready for Web, and CLI

  http :8080 user-agent:Mozilla/5.0
  # returns a React app when called from Browser,
  # together with browser for captured CloudEvents
  
  http :8080
  # returns a JSON with app's coordinates when called from command line

Supporting features

• K8s readyness and liveness probes

  http :8080/health/ready
  http :8080/health/live

• Prometeus metrics

  http :8080/metrics

• OpenAPI & Swagger UI

  http :8080/openapi.json
  http :8080/swagger-ui

• Input validation (validation by OpenAPI schema)

• Distributed Tracing

Architecture

We've prepared two backend implementations of the above feature. First one is implemented in Red Hat build of Quarkus framework and live in the quarkus directory. The second backend has been implemented in Express.JS, runs on Node, and lives in expressjs directory. Both of those backend are using single frontend, written in React framework, in Typescript.

├── quarkus/     # Quarkus backend
├── expressjs/   # Express.JS backend
├── frontend/    # React frontend
└── Makefile     # Main make file

The frontend application builds static Web files. They are packaged as Webjar in the user's Maven repository (~/.m2/repository). Thanks to that the Quarkus application is able to use those static files directly. The express backend needs to extract those webjar files.

showcase's Issues

Missed events in the startup of the React app

A loss of events can be observed in React component. After refresh of web browser, only the last event is being displayed:

When calling the endpoint from CLI all events are streamed:

$ http :8080/events
HTTP/1.1 200 OK
Cache-Control: no-cache
Connection: keep-alive
Content-Type: text/event-stream; charset=utf-8
Date: Thu, 13 Apr 2023 15:48:25 GMT
X-Powered-By: Express
X-SSE-Content-Type: application/cloudevents+json
transfer-encoding: chunked

data:{
    "data": {
        "a": {
            "b": "first"
        }
    },
    "datacontenttype": "application/json",
    "id": "41e1e914-bb01-41cb-83eb-5340d480c600",
    "source": "kn-event/v1.7.0",
    "specversion": "1.0",
    "time": "2023-04-13T15:45:13.216Z",
    "type": "dev.knative.cli.plugin.event.generic"
}

data:{
    "data": {
        "a": {
            "b": "second"
        }
    },
    "datacontenttype": "application/json",
    "id": "c34c0cd7-aa84-41e5-be30-cb07bea0a234",
    "source": "kn-event/v1.7.0",
    "specversion": "1.0",
    "time": "2023-04-13T15:45:19.460Z",
    "type": "dev.knative.cli.plugin.event.generic"
}

data:{
    "data": {
        "a": {
            "b": "third"
        }
    },
    "datacontenttype": "application/json",
    "id": "56141d84-01b7-46c5-bed2-13ae4761dc57",
    "source": "kn-event/v1.7.0",
    "specversion": "1.0",
    "time": "2023-04-13T15:48:21.141Z",
    "type": "dev.knative.cli.plugin.event.generic"
}
^C

I suspect this might be some kind of race in the following lines:

showcase/frontend/src/events/sse.ts

Lines 35 to 39 in a01a18c

	const sse = new EventSource(`${baseAddress}/events`, { withCredentials: true })
	sse.onmessage = (e: MessageEvent) => {
	const ce = new CloudEvent(JSON.parse(e.data))
	this.listeners.forEach((l) => l(ce))
	}

To reproduce:

1. Deploy an app
2. Send a few events, so you know their order (for example id==first, id==second, id=third)
3. Open/refresh the web page

Actual result

1. You will see just the last event being rendered

Expected result

1. You should see all the events collected, rendered properly

/kind bug

Add support for Distributed Tracing

Distributed tracing should be supported. Apps should support Open Telemetry tracing standard.

showcase/README.md

Line 86 in a01a18c

* [ ] Distributed Tracing

Received events should be logged in human-readable form

After the event is received by the showcase app, the event should be logged to the console in human-readable form. Best would be to log the event in the same way the Knative's event-display image does it:

☁️  cloudevents.Event
Validation: valid
Context Attributes,
  specversion: 1.0
  type: samples.http.mode3
  source: /apis/v1/namespaces/default/pingsources/ping-source
  id: e8fa7906-ab62-4e61-9c13-a9406e2130a9
  time: 2020-03-02T20:52:00.0004957Z
  datacontenttype: application/json
Data,
  {
    "id": 0,
    "message": "Hello world"
  }

Can't consume events from PingSource

How to reproduce:

kn service create event-consumer-web --image quay.io/openshift-knative/showcase --scale-min=1
kn source ping create ping-producer --data '{ "value": "Ping" }' --sink ksvc:event-consumer-web

This exception is raised for each ping in the user-container log:

2023-06-25 18:59:00,491 ERROR [org.jbo.res.rea.com.cor.AbstractResteasyReactiveContext] (executor-thread-0) Request failed: java.lang.NullPointerException
at java.base/java.util.Objects.requireNonNull(Objects.java:209)
at com.redhat.openshift.knative.showcase.events.Presenter.printData(Presenter.java:102)
at com.redhat.openshift.knative.showcase.events.Presenter.asHumanReadable(Presenter.java:41)
at com.redhat.openshift.knative.showcase.events.Presenter_ClientProxy.asHumanReadable(Unknown Source)
at com.redhat.openshift.knative.showcase.events.Rest.receive(Rest.java:33)
at com.redhat.openshift.knative.showcase.events.Rest.receiveOnIndex(Rest.java:40)
at com.redhat.openshift.knative.showcase.events.Rest_ClientProxy.receiveOnIndex(Unknown Source)
at com.redhat.openshift.knative.showcase.events.Endpoint$quarkusrestinvoker$receiveOnIndex_42942fa85a449e0db59f32cfee1e2510c2300c8b.invoke(Unknown Source)
at org.jboss.resteasy.reactive.server.handlers.InvocationHandler.handle(InvocationHandler.java:29)
at io.quarkus.resteasy.reactive.server.runtime.QuarkusResteasyReactiveRequestContext.invokeHandler(QuarkusResteasyReactiveRequestContext.java:115)
at org.jboss.resteasy.reactive.common.core.AbstractResteasyReactiveContext.run(AbstractResteasyReactiveContext.java:142)
at io.quarkus.vertx.core.runtime.VertxCoreRecorder$14.runWith(VertxCoreRecorder.java:576)
at org.jboss.threads.EnhancedQueueExecutor$Task.run(EnhancedQueueExecutor.java:2449)
at org.jboss.threads.EnhancedQueueExecutor$ThreadBody.run(EnhancedQueueExecutor.java:1478)
at org.jboss.threads.DelegatingRunnable.run(DelegatingRunnable.java:29)
at org.jboss.threads.ThreadLocalResettingRunnable.run(ThreadLocalResettingRunnable.java:29)
at io.netty.util.concurrent.FastThreadLocalRunnable.run(FastThreadLocalRunnable.java:30)
at java.base/java.lang.Thread.run(Thread.java:833

No (easy) way how to build the Docker image

This app is a showcase for Knative. One should be able to build the Docker image of the app using kn build, with both supported build strategies, using JVM mode or native build mode.

Right now, it is not possible to do this easily as there is the frontend dependency which is available only after building it locally (make frontend) in the local maven repo. kn build however cannot access the local maven repo and fails to fetch the artefact.

Event streaming shouldn't be limited to the number of threads in executor service

As discussed #11 (comment) the current implementation is limited to the number of threads in the executor service.

showcase/quarkus/src/main/java/com/redhat/openshift/knative/showcase/events/EventStore.java

Lines 17 to 27 in a01a18c

	private final ExecutorService executorService =
	Executors.newFixedThreadPool(12);
	Multi<CloudEvent> stream() {
	var p = new EventsPuller();
	return Multi.createBy()
	.repeating()
	.supplier(p::pull)
	.indefinitely()
	.runSubscriptionOn(executorService);
	}

It should be possible to rewrite it to better solution, which either:

• Make an 'artificial' stream that emits a 'heartbeat' every 25ms and only then wakes up, looks at events and goes to sleep. That should handle any number of calls on a single thread
• Use a different implementation of events that is event-driven, that is, it tells you when something appears in it. Maybe using MultiCreate#emitter(java.util.function.Consumer) is a good idea. We can use a factory like this and just call emit on it as we get the next event. The stream emits nothing, and everything non-blocking sleeps.

The health endpoints are missing at `/health/live`, and `/health/ready` for Quarkus

After some migration (guessing the Quarkus 2.x) the health endpoints have migrated to /q/health from previous /health.

Also, the health endpoints are missed in openapi.json file.

/kind bug

The native-standalone containerfile doesn't build on Buildah

Original: cardil/knative-serving-showcase#1

Building with Buildah fails (src/main/container/native-standalone/Containerfile):

$ buildah bud --layers \
  --ulimit nofile=4096:4096 \
  -f src/main/container/native-standalone/Containerfile .

The error message is:

[INFO] Tests run: 4, Failures: 0, Errors: 0, Skipped: 0
[INFO] 
[INFO] 
[INFO] --- maven-failsafe-plugin:3.0.0-M7:verify (default) @ knative-serving-showcase ---
[INFO] ------------------------------------------------------------------------
[INFO] BUILD SUCCESS
[INFO] ------------------------------------------------------------------------
[INFO] Total time:  03:45 min
[INFO] Finished at: 2023-01-13T13:49:28Z
[INFO] ------------------------------------------------------------------------
--> 948c359604a
[2/2] STEP 1/7: FROM registry.access.redhat.com/ubi8/ubi-minimal:8.7
[2/2] STEP 2/7: WORKDIR /work
--> Using cache 9fa937ced8dcee485b5ec047518f2945368d2fb83c3e156b7b0263814b22b82d
--> 9fa937ced8d
[2/2] STEP 3/7: COPY --from=builder /project/work/target/*-runner /work/application
Error: building at STEP "COPY --from=builder /project/work/target/*-runner /work/application": checking on sources under "/home/ksuszyns/.local/share/containers/storage/overlay/ad4e84047a6b023f1f67bf14dbcd1f329a8f52bb086fadbea199326278c40b31/merged": Rel: can't make  relative to /home/ksuszyns/.local/share/containers/storage/overlay/ad4e84047a6b023f1f67bf14dbcd1f329a8f52bb086fadbea199326278c40b31/merged; copier: stat: ["/project/work/target/*-runner"]: no such file or directory

Execution: https://github.com/cardil/knative-serving-showcase/actions/runs/3902164920/jobs/6664892868

The `GREET` env param should influnce `GET /` response

To fix SRVKS-977, we need to have an env parameter, that will influence the GET / response. That's required so the end-users can easily verify environmental variable processing in the docs.

/kind feature

Consider moving the K8x manifest examples to the top folder

There are some example Kubernetes manifests:

https://github.com/openshift-knative/showcase/tree/86e484eee57c45301a9d78ab8a0aea7402789318/quarkus/src/main/kubernetes

Maybe they should be moved to the top level, to be easier to find. Also, a bit of documentation about them will be helpful.

Container images should be built by makefiles, and mostly on amd64 platform

As discussed in #11 (comment) the build could be enhanced.

Now we are building both frontend and backend for every platform we support. This takes a long time, especially on emulated platforms.

In theory, we could just build it once (on linux/amd64), and then just create a simple multi-arch image from the build artifacts. Both JVM, and TS/JS support the "build once, run everywhere" feature.

Unfortunately, it is not possible with this approach of using FROM ... as frontend/builder, and COPY --from=builder ... because the container engine errors saying it doesn't have an image for given architecture.

Maybe we can achieve that by utilizing volumes, for passing down the artifacts. In that way, we can build frontend, and backend apps once and then just create a multi-arch container image.

Also, as pointed out by @mgencur #11 (comment) it would be a good idea to be able to build them from makefiles, to not over rely on GH actions, and also make it easier to develop.

Make README clear and understandable

The current README is fairly rudimentary, as clearly evidenced by the number of questions and discussions raised in #11.

The README should be clear, and verbose enough, understandable both for contributors and for end-users. I think it should contain the explanations on how to use the showcase app to demo Knative as well.

We should point out the features of this app, and how they map to the features of Knative.

Express app doesn't support event collector at `POST /`

Introduced event collector in #11 should be working for POST /events and for POST /. The Express flavor lacks the POST /events endpoint.