Docker Cookbook

138 | Chapter 5: Kubernetes

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5.4 Starting Containers on a Kubernetes Cluster with Pods
Problem
You know how to start containers by using the Docker command-line interface. Now
you would like to use Kubernetes to schedule your containers in a cluster.
Solution
You have a Kubernetes cluster available to you, either through 
Recipe 5.3
 or 
Recipe
5.9
 or a public cloud provider like Google Container Engine. In addition, you have
downloaded the Kubernetes client 
kubectl
and it is set up to use your cluster end‐
point with the appropriate authentication (see 
Recipe 5.15
).
As explained in 
Recipe 5.1
, containers are scheduled as a group by defining pods.
Therefore, to start your first container, you need to write a pod definition in JSON or
YAML and use the 
kubectl
client to submit it to the Kubernetes API server.
Let’s start with a fun example and run the 2048 game. A Docker image is available on
the 
Docker Hub
, and I will leave it to you to check out the Dockerfile. Save the YAML
file shown here as 
2048.yaml
:
apiVersion: v1
kind: Pod
metadata:
name: 
"2048"
spec:
containers:
- image: cpk1224/docker-2048
name: 
"2048"
ports:
- containerPort: 80
hostPort: 80
You can now submit it to your cluster:
$ kubectl create -f 2048.yaml
pods/2048
Once the image is downloaded, the container will start running. You should be able
to use your browser and open the 2048 game on the IP of the host that is running it.
You will need to open any firewall rules that may prevent you from doing so.
Discussion
The YAML file specifies the API version (i.e., 
v1
) and the kind of object it defines
(i.e., pod). Then some metadata needs to be set to specify a name for this pod. In this
example, a single container is started, but there could be several. All would be defined