Blue-Green Deployments with Service Selectors

Application Deployment / Guide 17 of 44 / Intermediate

• Kubernetes1.36.4
• Cluster4 nodes
• Runtimecontainerd 2.2.6
• CNICalico v3.32.1
• TimeAbout 14 min

A Service selector is plain equality on Pod labels, re-evaluated continuously by the endpoints controller. Patching it does not restart anything and does not touch either Deployment - the EndpointSlice is simply recomputed, typically within a second.

This guide includes

Use this when a release has to switch over instantly and roll back just as fast. This matters because blue-green needs no special tooling in Kubernetes - a Service selector is plain label equality, re-evaluated continuously, so one patch moves all of the traffic.

• running two versions at once, sharing one label and differing by another
• confirming the Service selects only one of them, and reading its EndpointSlice
• flipping the entire cutover with a single patch to the Service selector
• rolling back with that same patch and the old value

Before you start

• A cluster and kubectl.
• The session creates namespace ckad-bg with Deployments blue and green (two replicas each, serving different text), a Service site selecting blue, and a client Pod.

1. 1

   Two versions running at once

2. 2

   The Service only sees one of them

3. 3

   Flip it

4. 4

   And back

Official sources

• Service
• Deployments
• kubectl patch