Blue/Green Deployment

We can create our "blue" deployment by saving the following yaml to a file blue.yaml.

apiVersion: extensions/v1beta1
kind: Deployment
metadata:
  name: nginx-1.10
spec:
  replicas: 3
  template:
    metadata:
      labels:
        name: nginx
        version: "1.10"
    spec:
      containers: 
        - name: nginx
          image: nginx:1.10
          ports:
            - name: http
              containerPort: 80

You can then create the deployment using the kubectl command.

$ kubectl apply -f blue.yaml

Save this to service.yaml.

apiVersion: v1
kind: Service
metadata: 
  name: nginx
  labels: 
    name: nginx
spec:
  ports:
    - name: http
      port: 80
      targetPort: 80
  selector: 
    name: nginx
    version: "1.10"
  type: LoadBalancer

Creating the service will create a load balancer that is accessible outside the cluster.

$ kubectl apply -f service.yaml

For the "green" deployment we will deploy a new deployment in parallel wit the "blue" deployment. If the following is in green.yaml...

apiVersion: extensions/v1beta1
kind: Deployment
metadata:
  name: nginx-1.11
spec:
  replicas: 3
  template:
    metadata:
      labels:
        name: nginx
        version: "1.11"
    spec:
      containers: 
        - name: nginx
          image: nginx:1.11
          ports:
            - name: http
              containerPort: 80

... I can create the new deployment like so.

$ kubectl apply -f green.yaml

To cut over to the "green" deployment we will update the selector for the service. Edit the service.yaml and change the selector version to "1.11". That will make it so that it matches the pods on the "green" deployment.

apiVersion: v1
kind: Service
metadata: 
  name: nginx
  labels: 
    name: nginx
spec:
  ports:
    - name: http
      port: 80
      targetPort: 80
  selector: 
    name: nginx
    version: "1.11"
  type: LoadBalancer

This apply will update the existing nginx service in place.

$ kubectl apply -f service.yaml

Automating

#!/bin/bash

# bg-deploy.sh <servicename> <version> <green-deployment.yaml>
# Deployment name should be <service>-<version>

DEPLOYMENTNAME=$1-$2
SERVICE=$1
VERSION=$2
DEPLOYMENTFILE=$3

kubectl apply -f $DEPLOYMENTFILE

# Wait until the Deployment is ready by checking the MinimumReplicasAvailable condition.
READY=$(kubectl get deploy $DEPLOYMENTNAME -o json | jq '.status.conditions[] | select(.reason == "MinimumReplicasAvailable") | .status' | tr -d '"')
while [[ "$READY" != "True" ]]; do
    READY=$(kubectl get deploy $DEPLOYMENTNAME -o json | jq '.status.conditions[] | select(.reason == "MinimumReplicasAvailable") | .status' | tr -d '"')
    sleep 5
done

# Update the service selector with the new version
kubectl patch svc $SERVICE -p "{\"spec\":{\"selector\": {\"name\": \"${SERVICE}\", \"version\": \"${VERSION}\"}}}"

echo "Done."

References

https://www.ianlewis.org/en/bluegreen-deployments-kubernetes