Estimated time: 26 min remaining
The replication controller is a critical (and awesome) piece of the Kubernetes architecture.
The replication controller is responsible for ensuring that a specified number of pod "replicas" are running at any given time (more on that in the next section) and it will create or delete replicas to reach the desired state.
To create the Replication Controller, the following needs to be done:
nano replicationController.jsonPaste the contents of this gist into the file, replace the PROJECT_ID, and save.
kubectl create -f replicationController.json
replicationcontroller "hello-node" createdBy default, the pod is only accessible by its internal IP within the cluster. In order to make the hello-node container
accessible from outside the kubernetes virtual network, you have to expose the pod as a kubernetes service.
We can expose the pod with the kubectl expose command and the --type="LoadBalancer" flag
which creates an external IP to accept traffic:
$ kubectl expose rc hello-node --type="LoadBalancer"The flag used in this command specifies that we’ll be using the load-balancer provided by the underlying infrastructure
(in this case the Compute Engine load balancer) and
“rc” is a reference to the replication controller.
The Kubernetes master creates the load balancer and related Compute Engine forwarding rules, target pools, and firewall rules to make the service fully accessible from outside of Google Cloud Platform.
More details on defining and configuring replication controllers can be found here.
Note: If you’re interested in what Container Engine does under the covers with Compute Engine VMs, you can check how
all of your VMs are tagged with a common prefix (kubectl get nodes). This tag can be used to operate on all of the VMs
in your container cluster with a single command.
To find the publicly-accessible IP address of the service, simply request kubectl to list the hello-node cluster service:
$ kubectl get services
NAME CLUSTER_IP EXTERNAL_IP PORT(S) SELECTOR AGE
hello-node 10.3.246.12 23.251.159.72 8080/TCP run=hello-node 53s
kubernetes 10.3.246.12 <none> 443/TCP 21mNote there are 2 IP addresses listed, both serving port 8080. One is the internal IP that is only visible inside your
cloud virtual network; the other is the external load-balanced IP. In this example, the external
IP address is 23.251.159.72.
You should now be able to reach the service by pointing your browser to this address: http://<EXTERNAL_IP>:8080
