UPDATE (2015/07/13): Now using the v1 API.

Cross posted on medium

I was trying to get a Go app running on Container Engine and couldn't quite find what I was looking for. There are guides out there about how to use Go and Docker, and how to use Kubernetes but but not many about Go apps and Container Engine. I also found it easy to deploy apps but most guides lacked information on best practices for how to maintain apps through regular upgrades so I decided to research it and write a post about it myself.

Be sure to check out the Container Engine documentation for details about the concepts and commands used.

This post is a continuation of the Deploying Go servers with Docker article on the Go blog. Make sure you run through building the Docker image.

Pushing the Docker Image to Google Container Registry

You will need the gcloud tool so make sure you have the Google Cloud SDK installed. Next you'll need to create a project on the Google Developers Console. Make note of the project id.

Set up your gcloud tool with the right config. Replace <project-id> below with your project id. Replace <zone> with the zone of your choosing:

$ gcloud config set project <project-id>
$ gcloud config set compute/zone <zone>

Once you have that done you will need to tag the image using docker.

$ docker tag outyet gcr.io/<project-id>/outyet:v1

This will set the repository and tag it with the version 'v1'. Next push the image to the registry. You may get warnings about installing the preview components. Just say 'yes' to install them when asked.

$ gcloud preview docker push gcr.io/<project-id>/outyet:v1

Kubernetes Configuration

We will create a replication controller and service for our app.

The replication controller configures how our app will be run and maintained in Kubernetes and the service allows our containers to be accessed as one logical service/app. Create a outyet-rc.yml file with the contents below. We will use the new v1 version of the API:

kind: ReplicationController
apiVersion: v1
metadata:
  name: outyet-v1
spec:
  replicas: 3
  selector:
    name: outyet
    version: "1"
  template:
    metadata:
      labels:
        name: outyet
        version: "1"
    spec:
      containers:
        - image: gcr.io/<project-id>/outyet:v1
          name: outyet
          ports:
            - containerPort: 8080
              hostPort: 8080
              protocol: TCP

Next we'll create a service for our app. Create an outyet-service.yml with the contents below:

kind: Service
apiVersion: v1
metadata:
  name: outyet
  labels:
    name: outyet
spec:
  ports:
    - port: 80
      targetPort: 8080
      protocol: TCP
  selector:
    name: outyet
  type: LoadBalancer

Deploy the Container Engine Cluster

Next we'll deploy our container engine cluster. We'll use the gcloud tool again. You may get warnings about installing the alpha components. Just say 'yes' to install them when asked.

$ gcloud alpha container clusters create outyet
$ gcloud config set container/cluster outyet

Create the Replication Controller

After the cluster is created we can deploy the app. First we will create the replication controllers:

$ gcloud alpha container kubectl create -f outyet-rc.yml

It will take a few minutes for the pods to come up. You can see if the pods are ready using the following command:

$ gcloud alpha container kubectl get pods

The pods will say their state is Pending at first but will change to Running when they are ready.

Create the Service

Create the service with the following command.

$ gcloud alpha container kubectl create -f outyet-service.yml

After the service is created we can see that it is created by viewing the output of this command:

$ gcloud alpha container kubectl get services

The service uses the LoadBalancer feature of Container Engine to set up a network loadbalancer to our service. We can get the external IP of the service using the following command:

$ gcloud compute forwarding-rules list

This will show the IP address of our service. Make note of the IP address. Finally we can create a firewall rule to allow access to our nodes:

$ gcloud compute firewall-rules create outyet-http --allow tcp:80 --target-tags k8s-outyet-node

Now we can view the app at http://<IP Address>/

Is Go 1.4 out yet? Yes!

Upgrading the App

Go 1.4 is already out yet so app isn't really exciting. Let's update it so it checks for Go 1.5. Lets override the CMD for the Dockerfile so it looks like this:

FROM golang:onbuild
CMD ["go-wrapper", "run", "-version=1.5"]
EXPOSE 8080

Next we will build, tag and push the updated docker image:

$ docker build -t outyet .
$ docker tag outyet gcr.io/<project-id>/outyet:v2
$ gcloud preview docker push gcr.io/<project-id>/outyet:v2

Next lets update all the places it says v1 in our outyet-rc.yml and change it to v2.

kind: ReplicationController
apiVersion: v1
metadata:
  name: outyet-v2
spec:
  replicas: 3
  selector:
    name: outyet
    version: "2"
  template:
    metadata:
      labels:
        name: outyet
        version: "2"
    spec:
      containers:
        - image: gcr.io/<project-id>/outyet:v2
          name: outyet
          ports:
            - containerPort: 8080
              hostPort: 8080
              protocol: TCP

Next do a rolling update of our replication controller outyet-v1 to our new outyet-v2:

$ gcloud alpha container kubectl rollingupdate outyet-v1 -f outyet-rc.yml --update-period=10s

This should take about 30 seconds to run as we have 3 replicas and we've set the update period as 10 seconds per replica.

After that runs we can refresh our app again to see if Go 1.5 is out yet :)

Is Go 1.5 out yet? No :(

Cleanup

Make sure you delete your cluster so you don't get charged too much money :)

$ gcloud alpha container clusters delete outyet

Conclusion

I really think containers are the way everyone will be developing apps in the future so hopefully that gave you an idea of how you can deploy a Go app and upgrade it using Container Engine. As a next step try out some of the many example apps available in the Kubernetes repo.