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Deploying multiple instances of an application

Earlier, you learned that a pod consists of one or more containers deployed together on one host, and is the smallest compute unit that can be defined, deployed, and managed. You also learned you could scale the number of pods up and down which adds a layer of resiliency. But as noted by the definition of a pod, they are running on a single host. To obtain more resiliency and availability of an application, you can create multiple deployments of an image and load balance traffic to those instances. In this next section, deploy another instance of the NGINX image.

  1. Return to the Developer perspective in the OpenShift web console.

  1. Click +Add in the left-hand taskbar.
  2. Click the View all samples link on the Getting started resources tile.

  1. Click the NGINX tile.
  2. Change the Name field from nginx-sample to nginx-server-2. 
    nginx-server-2
  3. Click Create.

  1. Click Topology in left-hand taskbar.

Wait for the deployment to complete (solid dark blue outer ring on the deployment icon).

  1. Click the center of the newly created nginx-server-2 deployment.
  2. Click the Resources tab.
  3. Click the name of the running Pod to display more information.

  1. Click the Terminal tab.

Next, change the content of the default page displayed when the NGINX web server is accessed like you did earlier with the first server. This will allow you to easily tell which NGINX deployment you are accessing.

  1. Click inside the Terminal window (black box with a prompt like sh-4.2$).
  2. Issue the following commands in the Terminal to modify the web server's default page. You will first create a backup copy of the original file in case you want to revert back to it later.
cp index.html index.html.orig
echo NGINX Server 2 works! > index.html
ls
Example output

sh-4.2$ cp index.html index.html.orig sh-4.2$ echo NGINX Server 1 works! > index.html sh-4.2$ ls README.md index.html index.html.orig nginx-start openshift sh-4.2$

  1. Click Topology in left-hand task bar of OpenShift web console.
  2. Click the Open URL button on the edge of the nginx-server-2 deployment icon. This will launch as a new tab or window in your web browser. You should now see the default page for the web server displays the new message: NGINX Server 2 works!

In the next section you will create a route to load balance network traffic between the two NGINX web servers.