Blue/green Deployment

Blue/green deployment quoted from TechTarget

A blue/green deployment is a change management strategy for releasing software code. Blue/green deployments, which may also be referred to as A/B deployments require two identical hardware environments that are configured exactly the same way. While one environment is active and serving end users, the other environment remains idle.

Container technology offers a stand-alone environment to run the desired service, which makes it super easy to create identical environments as required in the blue/green deployment. The loosely coupled Services - ReplicaSets, and the label/selector-based service routing in Kubernetes make it easy to switch between different backend environments. With these techniques, the blue/green deployments in Kubernetes can be done as follows:

Before the deployment, the infrastructure is prepared like so:

Prepare the blue deployment and green deployment with TOMCAT_VERSION=7 and TARGET_ROLE set to blue or green respectively.

apiVersion: extensions/v1beta1

kind: Deployment

metadata:

name: tomcat-deployment-${TARGET_ROLE}

spec:

replicas: 2

template:

metadata:

labels:

app: tomcat

role: ${TARGET_ROLE}

spec:

containers:

- name: tomcat-container

image: tomcat:${TOMCAT_VERSION}

ports:

- containerPort: 8080

readinessProbe:

httpGet:

path: /

port: 8080

Prepare the public service endpoint, which initially routes to one of the backend environments, say TARGET_ROLE=blue.

kind: Service

apiVersion: v1

metadata:

name: tomcat-service

labels:

app: tomcat

role: ${TARGET_ROLE}

env: prod

spec:

type: LoadBalancer

selector:

app: tomcat

role: ${TARGET_ROLE}

ports:

- port: 80

targetPort: 8080

Optionally, prepare a test endpoint so that we can visit the backend environments for testing. They are similar to the public service endpoint, but they are intended to be accessed internally by the dev/ops team only.

kind: Service

apiVersion: v1

metadata:

name: tomcat-test-${TARGET_ROLE}

labels:

app: tomcat

role: test-${TARGET_ROLE}

spec:

type: LoadBalancer

selector:

app: tomcat

role: ${TARGET_ROLE}

ports:

- port: 80

targetPort: 8080

Update the application in the inactive environment, say green environment. Set TARGET_ROLE=green and TOMCAT_VERSION=8 in the deployment config to update the green environment.

Test the deployment via the tomcat-test-green test endpoint to ensure the green environment is ready to serve client traffic.

Switch the frontend Service routing to the green environment by updating the Service config with TARGET_ROLE=green.

Run additional tests on the public endpoint to ensure it is working properly.

Now the blue environment is idle and we can:

leave it with the old application so that we can roll back if there's issue with the new application

update it to make it a hot backup of the active environment

reduce its replica count to save the occupied resources