Blue-Green Deployments in Kubernetes

Introduction

Deploying new versions of an application to production carries inherent risk. A Blue-Green Deployment is a release strategy that reduces downtime and risk by running two identical production environments called Blue and Green.

The Strategy

At any time, only one of the environments is live (receiving production traffic). Let's say Blue is currently live (v1.0).

1. You deploy the new version (v1.1) to the Green environment.
2. You run extensive automated tests on the Green environment to ensure v1.1 works perfectly.
3. Once Green is verified, you update the load balancer or router to instantly switch all user traffic from Blue to Green.
4. Green is now live. Blue becomes the idle environment.

If a critical bug is discovered in Green shortly after the switch, you can instantly rollback by switching the router back to Blue.

Implementing in Kubernetes

Kubernetes makes Blue-Green deployments incredibly straightforward using Services and Labels.

You have two Deployments:

• myapp-blue with label version: v1
• myapp-green with label version: v2

Your Kubernetes Service (which acts as the load balancer) determines where traffic goes based on its selector.

# The Service pointing to Blue
apiVersion: v1
kind: Service
metadata:
  name: myapp-service
spec:
  selector:
    app: myapp
    version: v1 # Currently points to Blue
  ports:
  - protocol: TCP
    port: 80

When you are ready to switch traffic to Green, you simply run kubectl apply with an updated Service YAML where version: v2. Kubernetes updates the iptables rules instantly, achieving a zero-downtime switch!

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