This is a pretty simple lab, we are going to explore labels. You can use labels to organize, group, or select API objects.
For example, pods are “tagged” with labels, and then services use label selectors to identify the pods they proxy to. This makes it possible for services to reference groups of pods, even treating pods with potentially different docker containers as related entities.
In a previous lab we added our web app using a S2I template. When we did that, OpenShift labeled our objects for us. Let’s look at the labels on our running pod.
$ oc get pods
$ oc describe pod/<POD NAME> | more
You can see the Labels automatically added contain the app, deployment, and deploymentconfig. Let’s add a new label to this pod.
$ oc label pod/<POD NAME> testdate=4.30.2018 testedby=mylastname
$ oc describe pod/<POD NAME> | more
$ oc describe all | grep -i "labels:"
Next let’s look at the log for the pod running our application.
testdate: 4.30.2018 testedby: mylastname
Your updated label will show up in the running pod’s.
Select Application -> Pods -> dc-metro-map (Running POD)
Labels will appear in the list:
That’s it for this lab. Now you know that all the objects in OpenShift can be labeled. This is important because those labels can be used as part of your CI/CD process. An upcoming lab will cover using labels for Blue/Green deployments. Labels can also be used for running your apps on specific nodes (e.g. just on SSD nodes or just on east coast nodes). You can read more about labels here and here.