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Skip Harness Label Selector Tracking on Kubernetes Deployments

Currently, this feature is behind the feature flag SKIP_ADDING_TRACK_LABEL_SELECTOR_IN_ROLLING. Contact Harness Support to enable the feature.You can prevent Harness from using its default Kubernetes label selector harness.io/track: stable during Canary deployments. Skipping this label can help when you have existing non-Harness deployed services or conflicts in naming.

Review: Labels in Harness Kubernetes Canary Phases​

Default Harness Kubernetes Canary deployments are a two phase process that relies on Deployment object labels for tracking.

First, let's review the two phase Canary deployment:

  1. Canary Phase:
    1. Harness creates a Canary version of the Kubernetes Deployment object defined in your Service Definition Manifests section.
    2. All pods in the Canary Phase have label the harness.io/track: canary. Traffic could be routed to these pods using this label.
    3. Once that Deployment is verified, the Canary Delete step deletes it by default.
      Using this method, Harness provides a Canary group as a way to test the new build, run your verification, and then roll out to the following Primary group.
  2. Primary Phase:
    1. Runs the actual Deployment using a Kubernetes Rolling Update with the number of pods you specify in the Manifests files (for example, replicas: 3).
    2. All pods in the Primary Phase have label harness.io/track: stable.

Review: Invalid Value LabelSelector​

Kubernetes labels are immutable. If a specific Deployment object already exists in the cluster, you cannot change its labels.

This can cause problems with the default Harness Kubernetes Canary deployments use of harness.io/track if the Deployment object already exists before the Harness deployment.

If you are deploying different Harness Deployment objects to the same cluster, you might encounter a Selector error such as this:

The Deployment “harness-example-deployment” is invalid: spec.selector:   
  Invalid value: v1.LabelSelector{MatchLabels:map[string]string{“app”:“harness-example”},   
  MatchExpressions:[]v1.LabelSelectorRequirement{}}: field is immutable

Most often, you can simply delete or rename the Deployment object. In some case, this can be a problem because you will have downtime when the object is restarted.

As an alternative, you can force Harness to skip the harness.io/track: stable label in the Canary deployment.

Skipping the Tracking Label​

Once the relevant feature flag is enabled, a Harness Kubernetes Canary deployment will work like this:

  • If the Deployment object already exists in the cluster without the harness.io/track: stable, Harness will not add the harness.io/track: stable label to the Deployment object.
  • If the Deployment object already exists with the harness.io/track: stable label, Harness will not delete it.
  • For any new Deployment object, Harness will not add the harness.io/track: stable label.