openshift-health-check-exercise

Exercise in adding health probes to an application in Openshift.

Goals

• Deploy an application with HTTP endpoints to openshift
• Add readiness and liveness probes to the application

Steps

Background

Setup

1. Log in to the CLI of Openshift as the developer user.
2. Create a new project, e.g. nodejs-helloworld
3. Deploy the nodejs app we used in web-console intro lab:

   $ oc new-app --name helloworld --env="WORLD_STATE=infected" svejkciber/nodejs-helloworld:00ce99e2badb634a700862bc97963a8d28032f46
   ...
   --> Success
    Application is not exposed. You can expose services to the outside world by executing one or more of thecommands below:
     'oc expose svc/helloworld'
    Run 'oc status' to view your app.
   

4. Verify that the app is running with oc status, oc get pod and view the running pod's log.
5. Expose an external HTTP route to the app (hint: just follow the advice given above)
6. Test the app with a web broser or curl (hint: get the DNS name of the route from oc get route).

Add HTTP readiness probe

Since the application's default HTTP endpoint normally returns 200 OK, we can simply reuse it for health probes. Note that this is somewhat quick and dirty, in realistic applications one would usually implement dedicated endpoints for each probe, e.g. /isReady and /isAlive .

1. Review Openshift's informational warning about missing health probes:

   $ oc status --suggest
   ...
   Info:
     * pod/helloworld-1-deploy has no liveness probe to verify pods are still running.
       try: oc set probe pod/helloworld-1-deploy --liveness ...
     * dc/helloworld has no readiness probe to verify pods are ready to accept traffic or ensure deployment is successful.
       try: oc set probe dc/helloworld --readiness ...
     * dc/helloworld has no liveness probe to verify pods are still running.
       try: oc set probe dc/helloworld --liveness ...
   

   We will fix these issues soon.
2. Add a readiness probe to the deployment configuration:

   $ oc set probe dc/helloworld --readiness --get-url=http://:8080/
   

3. Verify that the probe is added to the DeploymentConfiguration

   $ oc describe dc/helloworld
   ...
   Pod Template:
   Labels:       app=helloworld
   ...
   Containers:
    helloworld:
    ...
    Readiness:  http-get http://:8080/ delay=0s timeout=1s period=10s #success=1 #failure=3
    ...
   

   We have added a readines probe with default parameter.

Add a HTTP liveness probe

This step is identical to the above probe configuration, except that the prope type argument in step 2 is --liveness instead of --readiness.

Check that the project status is ok with respect to probes

Run oc status again to check that there are no more complaints of missing probes.

Bonus

1. Fork the Git repo of the nodejs-helloworld app at https://github.com/svejk-ciber/nodejs-helloworld.
2. Perform a source build from your forked repo in Openshift. The new-app command becomes something like:

   $ oc new-app --name <NAME> --env="WORLD_STATE=<SOME STATE>" https://github.com/svejk-ciber/nodejs-helloworld
   

   You may have to specify the docker source strategy, if Openshift doesn't pick up that this is a Dockerfile build.
3. Implement a couple of custom probe endpoints, e.g. /isAlive and isReady. Tweak the implementations so that the probes fail. Observe Openhsift/Kubernetes behaviour on failing probes and adjust the probe implementations.