Labels

Labels

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.

Labels on a pod

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.

Step 1

See Current labels

oc get pods
oc describe pod/<POD NAME> | grep Labels: --context=4
Namespace:    demo-1
Priority:     0
Node:         ip-10-0-132-38.us-east-2.compute.internal/10.0.132.38
Start Time:   Tue, 14 Apr 2020 17:41:58 +0000
Labels:       app=dc-metro-map
              deploymentconfig=dc-metro-map
              pod-template-hash=7bc46bf89d
Annotations:  k8s.v1.cni.cncf.io/networks-status:
                [{

You can see the Labels automatically added contain the app, deployment, and deploymentconfig. Let’s add a new label to this pod.

Step 2

Add a label

oc label pod/<POD NAME> testdate=4.14.2020 testedby=mylastname
Step 3

Look at the labels

oc describe pod/<POD NAME> | grep Labels: --context=4
Namespace:    demo-1
Priority:     0
Node:         ip-10-0-132-38.us-east-2.compute.internal/10.0.132.38
Start Time:   Tue, 14 Apr 2020 17:41:58 +0000
Labels:       app=dc-metro-map
              deploymentconfig=dc-metro-map
              pod-template-hash=7bc46bf89d
              testdate=4.14.2020
              testedby=mylastname
Click "Workloads",
click on "Pods",
Click on the three vertical dots next to the "Running" pod.
Consider filtering for Status "Running".
project
Click "Edit Labels"
Add 'testedby=mylastname'
click "Save"
project

Here, at the top, you can see the labels on this pod

project

Your updated label will show up in the running pods.

Select Workloads
select pods
select dc-metro-map (Running POD),
then scroll down to "Labels"
project

Summary

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).