Update OpenShift applications with zero downtime using a single command

Learning path | 3 resources | 30 mins | Published on February 27, 2024

Perform rolling updates of existing running applications, which means you can spin up a different version of an application—newer or older—than the current one, and have the traffic automatically routed to it.

In this activity, created by Don Schenck, you will deploy an application, actively use that application, and then initiate a rolling update to versions 2 and 3 of the application.

Try OpenShift in the Developer Sandbox

  1. Overview: Update OpenShift applications with zero downtime using a single command
  2. Deploy a Kubernetes rolling update Page | 15 mins
  3. Guarantee application availability with OpenShift readiness Page | 15 mins

Page

Guarantee application availability with OpenShift readiness

Kubernetes
Don Schenck
Guarantee Application Availability

Now that you have deployed your rolling update, you're ready to create readiness probes.

In order to get full benefit from taking this lesson, you need to:

In this lesson, you will:

  • Log in to your Developer Sandbox

  • Create a readiness probe

  • Run a curl command 

  • Change deployment image

  • Observe results

Log in to your OpenShift Sandbox at the command line

Log in to your OpenShift Sandbox by following these instructions.

Create a readiness probe for an existing deployment

Run the following command to create the readiness probe:

oc set probe deploy/myboot --readiness --get-url=http://:8080/health

Run a curl command loop to view the application output

  1. Run the following command to see the URL of the application:

    oc get routes

    You will see output similar to the following:

    NAME     HOST/PORT                                                                    PATH   SERVICES   PORT   TERMINATION   WILDCARD
myboot   myboot-rhn-engineering-dschenck-dev.apps.sandbox.x8i5.p1.openshiftapps.com          myboot     http                 None

  2. We will now run a curl command loop against this URL to see the application output. Replace the URL in the following command based on the results of the previous command (oc get routes) and enter it at a command line.

    If you are using Bash:

    for ((i=1;i<=10000;i++)); do curl http://myboot-rhn-engineering-foo-dev.apps.sandbox.x8i5.p1.openshiftapps.com; sleep .01; done;

    If you are using PowerShell:

    while ($true) { (curl myboot-rhn-engineering-foo-dev.apps.sandbox.x8i5.p1.openshiftapps.com).content;start-sleep -Milliseconds 200; }

Change deployment image to version 3

Run the following command to switch to the version 3 image for the myboot application:

oc set image deploy/myboot myboot=quay.io/rhdevelopers/myboot:v3

Observe rolling deployment results

As the command above is processed, you will see the output of the curl loop change. This is a result of the rolling update with zero downtime.

Congratulations. You've learned how to perform rolling updates of running applications and created readiness probes to guarantee your application's availability. The result? You can now update your OpenShift applications with a single command.

Learn more

Learn more about Kubernetes probes from these Red Hat resources:

Previous resource
Deploy a Kubernetes rolling update