# 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>


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