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Traffic switching via label selectors

Traffic switching via label selectors is a technique used in Kubernetes to control service routing without modifying the Service object's IP address. This method is a core component of implementing deployment strategies such as Blue/Green Deployment.^[400-devops-06-kubernetes-k8s-ithelp-day14-readme.md]

Mechanism

Kubernetes Services direct network traffic to a set of Pods based on label selectors. By updating the spec.selector field in a Service configuration, an administrator can immediately change the destination Pod group.^[400-devops-06-kubernetes-k8s-ithelp-day14-readme.md]

This allows for instant traffic redirection because the Service's virtual IP (ClusterIP) remains constant, while the underlying Pods that satisfy the selector criteria change.^[400-devops-06-kubernetes-k8s-ithelp-day14-readme.md]

Implementation Workflow

When using this method to switch traffic from an old version (v1) to a new version (v2), the process typically follows these steps^[400-devops-06-kubernetes-k8s-ithelp-day14-readme.md]:

  1. Deploy v1: Run the initial version of the application and configure the Service selector to point to the v1 Pods (e.g., version: v1).
  2. Deploy v2: Launch the new version of the application while v1 is still running. Ensure the v2 Pods are fully ready and running.
  3. Switch Selector: Update the Service's selector field to match the labels of the v2 Pods (e.g., changing version: v1 to version: v2).
  4. Cleanup: After verifying that traffic is successfully routing to v2, terminate the old v1 resources.

Key Considerations

  • Resource Overhead: During the transition phase, both v1 and v2 versions run simultaneously. This requires the cluster to have sufficient resources to handle the extra load temporarily.^[400-devops-06-kubernetes-k8s-ithelp-day14-readme.md]
  • Zero Downtime: Because the new version is fully started before traffic is switched, this strategy facilitates Zero Downtime deployment.^[400-devops-06-kubernetes-k8s-ithelp-day14-readme.md]
  • Instant Cutover: The switch in traffic happens immediately upon applying the Service configuration update.^[400-devops-06-kubernetes-k8s-ithelp-day14-readme.md]

Sources

  • 400-devops-06-kubernetes-k8s-ithelp-day14-readme.md