4-guestbook

Lab 4: Guestbook with Knative

A simple web app written in Go that demonstrates how to deploy Redis (using vanilla Kubernetes components) alongside a Knative Service that relies on it. The guestbook application shows a page with a form that allows users to leave a message under a name of their choosing. Names and messages map to keys and values in Redis, so only one message per user is saved at a time.

Deploy Redis

Although the configuration in this sample is intentionally very simple, Redis can require relatively complex configuration that Knative does not support. Luckily, Knative allows you to mix and match Knative components with vanilla Kubernetes components.

The Redis configuration consists of two parts:

• Deployment: contains a minimal configuration for a single Redis instance, named redis-master.

• Service: contains a Kubernetes Service that finds redis-master by its name and role labels and routes requests to it. The REDIS_HOST environment variable in guestbook.yaml refers to the name of the Service, also named redis-master, not the name of the Deployment.

Note: Don't confuse a Kubernetes Service with a Knative Service. A Knative Service handles the deployment, scaling, and routing for a workload. A Kubernetes Service routes requests to an existing deployment.

Deploy this to you Kubernetes cluster using kubectl:

kubectl apply -f redis.yaml

Deploy the Guestbook Application

As with the previous lab assignments this too uses the Knative Build and [Serve][knative-serve] components in order to build the Guestbook application from soure and running it in one go.

Simply deploy the Guestbook application by running the following command:

kubectl apply -f guestbook.yaml

Exploring

Note: the following example uses curl to make requests to the application. You can also use your browser by following the steps in the routing sample to route requests to / to the guestbook Service.

To access this service, you need to determine its ingress address:

kubectl get svc istio-ingressgateway -n istio-system

When the service is ready, you'll see an IP address in the EXTERNAL-IP field:

NAME                     TYPE           CLUSTER-IP     EXTERNAL-IP      PORT(S)                                      AGE
istio-ingressgateway   LoadBalancer   10.23.247.74   35.203.155.229   80:32380/TCP,443:32390/TCP,32400:32400/TCP   2d

Once the EXTERNAL-IP gets assigned to the cluster, you can run:

# Put the host name into an environment variable.
export SERVICE_HOST=`kubectl get route guestbook -o jsonpath="{.status.domain}"`
# Put the ingress IP into an environment variable.
export SERVICE_IP=`kubectl get svc istio-ingressgateway -n istio-system -o jsonpath="{.status.loadBalancer.ingress[*].ip}"`

Now use curl with the service IP as if DNS were properly configured:

curl --header "Host:$SERVICE_HOST" http://${SERVICE_IP}
# [...]
# <form action="/" method="post">
#  <div>Name: <input name="name"></div>
#  <div>Message: <input name="message"></div>
#  <input type="submit">
# </form>
# <ul>
#
# </ul>
# [...]

Note that the inputs are named name and message. You can use curl to POST data to the form as shown below:

curl -X POST -F "name=someone" -F "message=Hello, Knative!" --header "Host:$SERVICE_HOST" http://${SERVICE_IP}
# [...]
# <ul>
#   <li><strong>someone</strong>: Hello, Knative!</li>
# </ul>
# [...]

curl -X POST -F "name=knative_user" -F "message=I love Knative!" --header "Host:$SERVICE_HOST" http://${SERVICE_IP}
# [...]
# <ul>
#   <li><strong>knative_user</strong>: I love Knative!</li>
#   <li><strong>someone</strong>: Hello, Knative!</li>
# </ul>
# [...]

Cleaning up

When you're done, clean up the sample resources:

kubectl delete -f serving/samples/guestbook-redis-go/redis-deployment.yaml
kubectl delete -f serving/samples/guestbook-redis-go/redis-service.yaml
kubectl delete -f serving/samples/guestbook-redis-go/guestbook.yaml

Next Steps

For simplicity, this sample showed a configuration for Redis with a single server. In practice, that wouldn't scale very well for a real application. See the Kubernetes example repository for a more scalable deployment configuration for Redis on Kubernetes. That example does not include a service that allows other applications to connect to Redis, but you can use redis-service.yaml since it selects on the same name and role labels.

Alternatively, you may prefer to use a managed solution from your cloud provider (e.g. Cloud Memorystore). To access services outside of the cluster, you'll have to configure outbound network access.

Whichever way you go, you can use the guestbook container to test your Redis deployment. Just change the REDIS_HOST environment variable in guestbook.yaml to the correct host name.

Cleaning Up

To remove the Guestbook application and Redis service run the following commands:

kubectl delete --filename redis.yaml
kubectl delete --filename guestbook.yaml

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Lab 5: Serverless Runtime →

← Lab 3: Knative Events

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