OC use selector to handle applications - unix1998/technical_notes GitHub Wiki

In OpenShift, using labels and the oc scale command with the --selector option allows you to efficiently shut down (scale to 0) a group of applications that share a common characteristic. Here's the approach:

1. Label Your Applications:

  • The first step is to ensure the applications you want to manage as a group have a common label. This label acts as a marker to identify them as belonging to the same category.
  • You can add labels to deployments using the oc label command. For example:
oc label deployment/app1 app=myapp environment=staging
oc label deployment/app2 app=myapp environment=production

In this example, both deployments (app1 and app2) are labeled with app=myapp. This establishes the commonality you want to use for scaling.

2. Leverage oc scale with --selector:

Once your applications are labeled, you can use oc scale with the --selector option to target them based on the shared label. The --selector option allows you to specify a label selector expression.

Here's how to shut down (scale to 0) all deployments labeled with app=myapp:

oc scale deployment --selector=app=myapp --replicas=0

This command selects all deployments with the label app=myapp (including app1 and app2 in our example) and scales them down to 0 replicas, essentially shutting them down.

Benefits of Using Labels and oc scale:

  • Group Management: Labels enable you to manage a group of applications with similar characteristics efficiently, reducing the need to target them individually.
  • Scalability: The oc scale command combined with --selector provides a scalable way to shut down or scale multiple deployments at once.
  • Flexibility: You can create more complex label selectors using logical operators (AND, OR, NOT) and set comparisons (in, notin) to target even more specific groups of applications.

Additional Considerations:

  • Graceful Shutdown: By default, deployments have a grace period (typically 30 seconds) for pods to shut down gracefully before being forcefully terminated. You can adjust this grace period using the --grace-period flag with oc scale.
  • Testing: It's always a good practice to test your oc scale command with --selector on a non-production environment before applying it to critical applications.

In Conclusion:

By combining labels and the oc scale command with --selector, you can effectively shut down or scale a group of applications in OpenShift, simplifying application lifecycle management.