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Kubernetes Blue Green Swap Services Selectors

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The Kubernetes Blue Green Swap Services Selectors step updates service selectors to route production traffic to the new pod set and stage traffic to the old pod set. Run this step after validating the new version through the stage service.

Before you begin​

Before you configure the step, make sure you have the following in place:

  • A Kubernetes service: Go to Kubernetes services to set up service manifests and artifact source.
  • A Kubernetes infrastructure: Go to Kubernetes infrastructure to connect your cluster and namespace.
  • A Harness delegate in target cluster: The delegate runs deployment steps in the cluster.
  • Runtime configuration: Every Kubernetes stage requires a runtime block specifying the connector and namespace. Go to Kubernetes runtime configuration to understand the required fields.

Configure the step​

The Stable Service and Stage Service fields are auto-populated from the Blue Green Deploy step output when you use this step in a blue-green stage:

${{stage.steps.k8sBlueGreenDeployStep.output.outputVariables.stableService}}
${{stage.steps.k8sBlueGreenDeployStep.output.outputVariables.stageService}}

You do not need to change these values.

The following parameters are available on the step.

ParameterDescriptionRequired
NameDisplay name for this step in the stage canvas. Default: Kubernetes Blue Green Swap Services Selectors.Required
Stable ServiceThe name of the service currently receiving production traffic. Auto-populated from the Blue Green Deploy step output.Required
Stage ServiceThe name of the service currently receiving stage traffic. Auto-populated from the Blue Green Deploy step output.Required
Kubeconfig PathPath to the kubeconfig file. Default: ${{infra.kube_config_path}}.Optional
NamespaceTarget namespace where both services run. Default: ${{infra.namespace}}.Optional
Release NameName used to track Harness release history. Default: ${{infra.releaseName}}.Optional
Working DirectoryOptional working directory for the swap operation.Optional
Log LevelVerbosity of step logs. Default: info.Optional

How the step works​

The step updates the selector on each service to point to the new pod color:

  • The primary service selector changes from the old color to the new color, routing production traffic to the new pod set.
  • The stage service selector changes from the new color to the old color, routing stage traffic to the old pod set.

The color labels (harness.io/color: blue or harness.io/color: green) on the pod sets do not change; only the service selectors are updated. Both pod sets continue running after the swap.

Rollback​

In the rollback group, the step is pre-wired to the service names captured by the Blue Green Deploy step:

${{rollback.data.PLUGIN_STABLE_SERVICE}}
${{rollback.data.PLUGIN_STAGE_SERVICE}}

If the failure occurred before the swap, the rollback swap is a no-op and the old version continues serving traffic. If the swap had already occurred, the rollback re-swaps selectors to restore the previous version as primary. The pod sets are not deleted; only the service selectors change.

Advanced settings​

  • Timeout duration: Maximum time the step is allowed to run before being terminated.
  • On failure: Define what happens if the step fails, such as retry, mark as success, or abort.
  • Strategy: Configure a looping strategy to run this step over a list of values.
  • Conditional execution: Run this step only when a specified condition is true.

Next steps​

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