Knative Asynchronous Component

Warning: Experimental and still under development. Not meant for production deployment. Note: This component has only been functionally tested with Kourier and Istio as the networking layer. Other networking layers are currently untested but will be added.

This is an add-on component that, when installed, will enable your Knative services to be called asynchronously. You can set a service to be always or conditionally asynchronous. Conditionally asynchronous services will respond when the Prefer: respond-async header is provided as a part of the request, while always asynchronous services do not need a special header to be called asynchronously.

Architecture

When Knative Serving creates a service, one of the artifacts created is a KIngress for the service. The yaml for the KIngress will contain an annotation which is read by the networking controller (net-istio, net-countour, etc.). The ingress controller in our asynchronous component looks for KIngresses with the async.ingress.networking.knative.dev annotation. The ingress controller will then create a KIngress for Istio (annotated with istio.ingress.networking.knative.dev), which will be picked up by the net component (net-istio in the above case) to create the required istio components, such as a virtual service, to route asynchronous service calls appropriately. If the service is an always asynchronous service, then all requests are routed to the producer component.

The following is the request flow (seen in blue in the architecture diagram above)

1. A new request is made to the application url with the header Prefer: respond-async.
2. The gateway has been modified such that requests with this header are routed to a K8s service in the user namespace.
3. This K8s service routes the request to the producer component in the knative-serving namespace, while the producer component returns a 202 Accepted status to the user.
4. The Producer is responsible for writing to the queue.
5. The Redis Source component watches the queue for new requests.
6. The Redis Source component sends cloud events to our Consumer service
7. The consumer component reads the cloud event and synchronously makes the service call to the Knative Service.

Prerequisites

• A kubernetes environment, recommended version and sizing here
• Install ko

Install Knative Serving & Eventing to your cluster

1. https://knative.dev/docs/install/any-kubernetes-cluster/

Install the consumer and async controller components

1. Apply the following config files:

   ko apply -f config/async/100-async-consumer.yaml
   ko apply -f config/ingress/controller.yaml
   

Note: Kourier is the default ingress.

To change this edit the prefix of INGRESS_CLASS_NAME in the config/ingress/controller.yaml file.

For example change the default kourier:

 env:
 - name: INGRESS_CLASS_NAME
   value: kourier.ingress.networking.knative.dev

To istio:

 env:
 - name: INGRESS_CLASS_NAME
   value: istio.ingress.networking.knative.dev

Install the Redis source

Using a cloud based Redis instance

1. Follow the Getting Started - Install Instructions for the Redis Source.

2. Update the producer .yaml file with the value for the REDIS_ADDRESS.

3. Update the tls-secret.yaml file with the cert.pem data key from your cloud instance. This will be the same key used in Getting Started - Install instructions. You can then apply it to your cluster.

   kubectl apply -f config/async/tls-secret.yaml
   

4. There is a .yaml file in the async-component describing the RedisStreamSource. It points to the async-consumer as the sink. First, update the address value in this .yaml file. You can then apply it to your cluster.

   kubectl apply -f config/async/100-async-redis-source.yaml
   

For a local installation of Redis

1. Follow the Getting Started Instructions for the Redis Source. For the Example section, do not install the entire samples folder, as you don't need the event-display sink. Only install redis with: kubectl apply -f samples/redis.

2. Update the producer .yaml file with the value for the REDIS_ADDRESS. This should be redis.redis.svc.cluster.local:6379.

3. There is a .yaml file in the async-component describing the RedisStreamSource. It points to the async-consumer as the sink. First update the address to rediss://redis.redis.svc.cluster.local:6379. You can then apply it to your cluster.

   kubectl apply -f config/async/100-async-redis-source.yaml
   

Install the producer component.

1. Apply the producer config file to install the component:

   ko apply -f config/async/100-async-producer.yaml
   

Create your demo application

1. This can be any simple hello world application. There is a sample application that sleeps for 10 seconds in the test/app folder. To deploy, use the kubectl apply command:

   kubectl apply -f test/app/service.yml
   

   Alternatively you can deploy using a ko compiled image:

   ko apply -f test/app/koService.yaml  
   

2. Note that your application has an annotation setting the ingress.class as async.ingress.networking.knative.dev. This enables just this application to respond to the Prefer: respond-async header.

   networking.knative.dev/ingress.class: async.ingress.networking.knative.dev
   

3. Make note of your application URL, which you can get with the following command:

   kubectl get kservice helloworld-sleep
   

   Note: If you don't see the service make sure you are using the default namespace

4. (Optional) If you wanted every service newly created by knative to respond to the Prefer: respond-async header, you can configure Knative Serving to use the async ingress class for every service. See here for warnings and details on ingress class handling.

   kubectl patch configmap/config-network \
   -n knative-serving \
   --type merge \
   -p '{"data":{"ingress.class":"async.ingress.networking.knative.dev"}}'
   

   You can remove this setting by updating the ingress.class to null or by updating the ingress.class to the ingress.class you would like to use, for example kourier.

   kubectl patch configmap/config-network \
   -n knative-serving --type merge \
   -p '{"data":{"ingress.class":null}}'
   

   kubectl patch configmap/config-network \
   -n knative-serving \
   --type merge \
   -p '{"data":{"ingress.class":"kourier.ingress.networking.knative.dev"}}'
   

Test your application

1. Curl your application. Try both asynchronous and non asynchronous requests.

   curl helloworld-sleep.default.11.112.113.14.xip.io
   curl helloworld-sleep.default.11.112.113.14.xip.io -H "Prefer: respond-async" -v
   

2. For the synchronous case, you should see that the connection remains open to the client, and does not close until about 10 seconds have passed, which is the amount of time this application sleeps. For the asynchronous case, you should see a 202 response returned immediately.

Update your Knative service to be always asynchronous.

1. To set a service to always respond asynchronously, rather than conditionally requiring the header, you can add the following annotation in the .yml for the service.

   async.knative.dev/mode: always.async.knative.dev
   

2. You can find an example of this (commented) in the test/app/service.yml file. Uncomment the annotation async.knative.dev/mode: always.async.knative.dev.

3. Update the application by applying the .yaml file:

   kubectl apply -f test/app/service.yml
   

Test your application

1. Curl the application, this time without the Prefer: respond-async header. You should see a 202 response returned while some pods are spun up to handle your request.

   curl helloworld-sleep.default.11.112.113.14.xip.io -v
   

2. You can see the pods with kubectl get pods.

Performance testing information can be found in the performance test README.

Uninstalling the component

1. Remove the demo application

   kubectl delete -f test/app/service.yml
   

   You can verify deletion by checking the output of:

   kubectl get all --namespace=default | grep helloworld-sleep
   

2. If you previously set every service to respond to the Prefer: respond-async header, remember to remove this setting by updating ingress.class to null, the previous value, or by updating ingress.class to the ingress.class you would like to use, for example kourier.

   kubectl patch configmap/config-network \
   -n knative-serving --type merge \
   -p '{"data":{"ingress.class":null}}'
   

   kubectl patch configmap/config-network \
   -n knative-serving \
   --type merge \
   -p '{"data":{"ingress.class":"kourier.ingress.networking.knative.dev"}}'
   

3. Remove the producer component

   ko delete -f config/async/100-async-producer.yaml
   

   You can verify the deletion by checking the output of:

   kubectl get all --namespace=knative-serving | grep async-producer
   

4. Remove the RedisStreamSource and tls secret

   kubectl delete -f config/async/100-async-redis-source.yaml
   kubectl delete -f config/async/tls-secret.yaml
   

   You can verify deletion by checking the output of:

   kubectl get all --namespace=knative-serving | grep redis
   kubectl get secrets --namespace=knative-serving | grep tls
   

5. Remove the eventing-redis component - make sure you are using this command in the eventing-redis project

   ko delete -f source/config
   

   You can verify the deletion by checking the output of:

   kubectl get all --all-namespaces | grep redis
   

6. Remove the consumer and async controller components - back in the async component project.

   ko delete -f config/ingress/controller.yaml
   ko delete -f config/async/100-async-consumer.yaml
   

   You can verify deletion by checking the output of:

   kubectl get all --namespace=knative-serving | grep async-controller
   kubectl get all --namespace=knative-serving | grep async-consumer