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Distributed calculator using Knative Serving

Attribute Details
Dapr runtime version v1.5.0
Knative Serving version v1.0
Language Javascript, Python, Go, C#
Environment Kubernetes > v1.20

This is a distributed calculator application from Dapr quickstart using Knative Serving (with Kourier) to host React Calculator. This is built as a proof-of-concept to show how to use Knative Serving with Dapr.

Prerequisites

This sample requires you to have the following installed on your machine:

Also, unless you have already done so, clone the repository with the samples and cd into the right directory:

git clone https://github.com/dapr/samples.git
cd samples/knative-distributed-calculator

Step 1 - Make sure that your kubectl client is working

The first thing you need is an enabled Kubernetes cluster. This sample was tested on a fully-fledged cluster.

Once you have that make sure you get a positive response from the following kubectl command

kubectl get pods

This should either have output as No resources found in default namespace. or should list the pods running the default namespace.

Step 2 - Setup Dapr

Follow instructions to download and install the Dapr CLI and initialize Dapr.

Step 3 - Setup Knative Serving

Note: Here you can find full instruction of how to install and configure Knative Serving. All the information below in steps 3 and 4 is an excerpt from it which was used and tested.

Install Knative Serving CRDs

kubectl apply -f https://github.com/knative/serving/releases/download/knative-v1.0.0/serving-crds.yaml

Install Knative Serving Core

kubectl apply -f https://github.com/knative/serving/releases/download/knative-v1.0.0/serving-core.yaml

Install Knative Kourier - networking layer

kubectl apply -f https://github.com/knative/net-kourier/releases/download/knative-v1.0.0/kourier.yaml

Configure Knative to use Kourier

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

Verify installation

kubectl get pods -n knative-serving

All pods inside knative-serving namespace should have Running or Completed status.

Step 3 - Configure DNS for Knative

Fetch the External IP address by running the command

kubectl --namespace kourier-system get service kourier

Configure DNS

This sample was tested with real DNS. In this case, you need to take the External IP address from the previous step and add it to your DNS wildcard A record (e.g. *.knative.example.com).

Direct Knative to use that domain

Please change knative.example.com below to your domain.

kubectl patch configmap/config-domain \
  --namespace knative-serving \
  --type merge \
  --patch '{"data":{"knative.example.com":""}}'

Step 4 - Setup Distributed Calculator

Install Redis store

Follow these instructions to create and configure a Redis store.

Here is a quick excerpt from it using Helm:

helm repo add bitnami https://charts.bitnami.com/bitnami
helm repo update
helm install redis bitnami/redis

Install Distributed Calculator

Navigate to the deploy directory in this quickstart directory:

cd deploy

Deploy all of your resources:

kubectl apply -f .

Note: This is the same Distributed Calculator from quickstart except for the React deployment.

Verification

Get URL for your React application:

kubectl get service.serving

Example output:

NAME                   URL                                                        LATESTCREATED               LATESTREADY                 READY   REASON
calculator-front-end   http://calculator-front-end.default.knative.example.com    calculator-front-end-rev1   calculator-front-end-rev1   True

Make sure that READY is set to True. Otherwise, please wait until all the necessary components are configured by Knative. The address, in this case, is http://calculator-front-end.default.knative.example.com.

Navigate to this address with your browser and you should see the distributed calculator. Do some calculations to make sure that all works as expected.

Behind the scene

By default, Knative will scale to zero its workloads if there is no traffic to them. Wait for a couple of minutes and run the next command to list all pods in default namespace:

kubectl get pods

Example output:

NAME                           READY   STATUS    RESTARTS   AGE
addapp-86cfcb8969-mvzs8        2/2     Running   0          2d23h
divideapp-6b94b477f5-58n92     2/2     Running   0          2d23h
multiplyapp-545c4bc54d-n6vrd   2/2     Running   0          2d23h
redis-master-0                 1/1     Running   0          2d23h
redis-replicas-0               1/1     Running   0          2d23h
redis-replicas-1               1/1     Running   0          2d23h
redis-replicas-2               1/1     Running   0          2d23h
subtractapp-5c6c6bc4fc-wlbqv   2/2     Running   0          2d23h

As you can see, there are no calculator-front-end pods.

Navigate back to the address with your browser to generate some traffic.

Return back to and list all pods once again:

NAME                                                    READY   STATUS    RESTARTS   AGE
addapp-86cfcb8969-mvzs8                                 2/2     Running   0          2d23h
calculator-front-end-rev1-deployment-6fd89f78df-6ttr2   3/3     Running   0          6s
divideapp-6b94b477f5-58n92                              2/2     Running   0          2d23h
multiplyapp-545c4bc54d-n6vrd                            2/2     Running   0          2d23h
redis-master-0                                          1/1     Running   0          2d23h
redis-replicas-0                                        1/1     Running   0          2d23h
redis-replicas-1                                        1/1     Running   0          2d23h
redis-replicas-2                                        1/1     Running   0          2d23h
subtractapp-5c6c6bc4fc-wlbqv                            2/2     Running   0          2d23h

As you can see there is calculator-front-end-rev1-deployment-6fd89f78df-6ttr2 pod with 3 containers running inside: calculator-front-end, queue-proxy and daprd.