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The "cool" thing you came for, right?

https://martinfowler.com/bliki/BlueGreenDeployment.html

So we know how to edit deployments

k edit deployments/k8sapp

We can change the image to deploy different versions

...
image: engineyard/k8sapp:v1
...

...
image: engineyard/k8sapp:v2
...

And notice it take a little while for the old pods to get rotated and the URL to start returning results from the new version

k get pods

NAME                              READY     STATUS              RESTARTS   AGE
k8sapp-495960030-9jfhw            1/1       Terminating         0          4m
k8sapp-495960030-bf8rj            1/1       Terminating         0          4m
k8sapp-495960030-lnl9t            1/1       Terminating         0          4m
k8sapp-495960030-w9tbl            1/1       Running             0          4m
k8sapp-495960030-zf0mx            1/1       Running             0          4m
k8sapp-576962527-1kqb8            0/1       ContainerCreating   0          0s
k8sapp-576962527-1tmxs            1/1       Running             0          1s
k8sapp-576962527-54pkc            1/1       Running             0          1s
k8sapp-576962527-b389b            0/1       ContainerCreating   0          1s

curl k8sapp.${ENV_NAME}.my.ey.io

Let's "fix" that and make deployments instantaneous (or at least feel that way to the user)

Let's create a blue deployment and a green deployment

echo "apiVersion: extensions/v1beta1
kind: Deployment
metadata:
  name: k8sapp-blue
  labels:
    app: k8sapp-blue
spec:
  strategy:
    type: Recreate
  template:
    metadata:
      labels:
        app: k8sapp-blue
    spec:
      containers:
      - name: k8sapp-blue
        image: engineyard/k8sapp
        imagePullPolicy: Always
        ports:
        - containerPort: 5000
          name: k8sapp" | kubectl create -f -

echo "apiVersion: extensions/v1beta1
kind: Deployment
metadata:
  name: k8sapp-green
  labels:
    app: k8sapp-green
spec:
  strategy:
    type: Recreate
  template:
    metadata:
      labels:
        app: k8sapp-green
    spec:
      containers:
      - name: k8sapp-green
        image: engineyard/k8sapp
        imagePullPolicy: Always
        ports:
        - containerPort: 5000
          name: k8sapp" | kubectl create -f -

We can now scale the deployments, change the version of images running in each, and editing the services/k8sapp

Make the blue deployment use image image:engineyard/k8sapp:v1

k edit deployments/k8sapp-blue

change the service to point to blue

k edit services/k8sapp

...
selector:
  app: k8sapp-blue

Make the green deployment use image image:engineyard/k8sapp:v2

k edit deployments/k8sapp-green

change the service to point to green

k edit services/k8sapp

...
selector:
  app: k8sapp-green