=====Overview=====
As we discussed the pods and their manual deployment, I have to tell you something. Take a deep breath, ok...and sit probably :).

NO ONE WORKS WITH PODS

I will let that rest for a second....



Ok, now, what I mean. The reason, why no one works with pods is because, they are too granular. What if we need to put 5 replicas of that image on 5 workers. Well, there is something called Replication controller, which encapsulates the pod and add more features.

So let's see visual representation of what I mean:

{{ :replicationcontroller.png?400 |}}

With the replication controller, we can define N amount of replicas and the controller takes care of the rest. The controller will ensure our desired state (5 replicas) is always in place.

So how we do it ? Well the process is pretty similar to pods as it relies on them.

  - We create a manifest file
  - We present it to the API
  - The API do the rest

=====Configuration=====
As with the manual configuration of the pods, we have to prepare a little manifest file. I have prepared a simple one:

====Manifest File====
<Code:bash|Manifest file>
apiVersion: v1
kind: ReplicationController
metadata:
  name: hello-rc
spec:
  replicas: 5
  selector:
    app: hello-date
  template:
    metadata:
      labels:
        app: hello-date
    spec:
      containers:
      - name: hello-pod
        image: andonovj/httpserverdemo:latest
        ports:
        - containerPort: 1234
</Code>

The first information is about the replication controller. In our case:
  - it is Version 1
  - it is Replication Controller (you to believe :) ) 
  - It is called: "hello-rc"
  - It has 5 replicas, so it will configure 5 pods
  - It will run application called: "hello-date" defined in the template

Later we have a pod a template section which has:

  * Metadata
  * Specification

From here, you can orient I hope :)

You see that the replication controller gives us way more possibilities and furthermore it relies on the Pods as it is using them.

====Create Replication Controller====
The command to create the controller, once you have the YML/JSON file is pretty similar as the pod:

<Code:bash|Create RC>
ubuntu@k8s-master:~$ kubectl create -f rc.yml
replicationcontroller/hello-rc created
ubuntu@k8s-master:~$
</Code>

After that, we can check the status and the pods

<Code:bash|Create RC>
ubuntu@k8s-master:~$ kubectl get rc
NAME       DESIRED   CURRENT   READY   AGE
hello-rc   5         5         3       17s
ubuntu@k8s-master:~$ kubectl describe rc
Name:         hello-rc
Namespace:    default
Selector:     app=hello-date
Labels:       app=hello-date
Annotations:  <none>
Replicas:     5 current / 5 desired
Pods Status:  5 Running / 0 Waiting / 0 Succeeded / 0 Failed
Pod Template:
  Labels:  app=hello-date
  Containers:
   hello-pod:
    Image:        andonovj/httpserverdemo:latest
    Port:         8080/TCP
    Host Port:    0/TCP
    Environment:  <none>
    Mounts:       <none>
  Volumes:        <none>
Events:
  Type    Reason            Age   From                    Message
  ----    ------            ----  ----                    -------
  Normal  SuccessfulCreate  10m   replication-controller  Created pod: hello-rc-dlx7j
  Normal  SuccessfulCreate  10m   replication-controller  Created pod: hello-rc-2kqmm
  Normal  SuccessfulCreate  10m   replication-controller  Created pod: hello-rc-twz2w
  Normal  SuccessfulCreate  10m   replication-controller  Created pod: hello-rc-8rn9t
  Normal  SuccessfulCreate  10m   replication-controller  Created pod: hello-rc-j2swd
ubuntu@k8s-master:~$
</Code>

In our case, we have 5 pods on our 2 workers:

  * 2 on Worker 1
  * 3 on Worker 2

====Update Configuration====
We can update the configuration, by simply updating the YML/JSON file. For example, let's increase the replicas from 5 -> 10, firstly we update it in the YML/JSON file:

<Code:bash|Update Config>
spec:
  replicas: 10
</Code>

After that, we simply apply that change:

<Code:bash|Apply the changes>
ubuntu@k8s-master:~$ kubectl apply -f rc.yml
Warning: kubectl apply should be used on resource created by either kubectl create --save-config or kubectl apply
replicationcontroller/hello-rc configured
ubuntu@k8s-master:~$
</Code>

You can ignore the warning line :) You can check the configuration as follows:

<Code:bash|Check the status>
ubuntu@k8s-master:~$ kubectl get rc
NAME       DESIRED   CURRENT   READY   AGE
hello-rc   10        10        10      16m
ubuntu@k8s-master:~$ kubectl describe rc
Name:         hello-rc
Namespace:    default
Selector:     app=hello-date
Labels:       app=hello-date
Annotations:  Replicas:  10 current / 10 desired
Pods Status:  10 Running / 0 Waiting / 0 Succeeded / 0 Failed
Pod Template:
  Labels:  app=hello-date
  Containers:
   hello-pod:
    Image:        andonovj/httpserverdemo:latest
    Port:         1234/TCP
    Host Port:    0/TCP
    Environment:  <none>
    Mounts:       <none>
  Volumes:        <none>
Events:
  Type    Reason            Age   From                    Message
  ----    ------            ----  ----                    -------
  Normal  SuccessfulCreate  16m   replication-controller  Created pod: hello-rc-dlx7j
  Normal  SuccessfulCreate  16m   replication-controller  Created pod: hello-rc-2kqmm
  Normal  SuccessfulCreate  16m   replication-controller  Created pod: hello-rc-twz2w
  Normal  SuccessfulCreate  16m   replication-controller  Created pod: hello-rc-8rn9t
  Normal  SuccessfulCreate  16m   replication-controller  Created pod: hello-rc-j2swd
  Normal  SuccessfulCreate  73s   replication-controller  Created pod: hello-rc-zhngb
  Normal  SuccessfulCreate  73s   replication-controller  Created pod: hello-rc-vxzfl
  Normal  SuccessfulCreate  73s   replication-controller  Created pod: hello-rc-dklgj
  Normal  SuccessfulCreate  73s   replication-controller  Created pod: hello-rc-cf8jw
  Normal  SuccessfulCreate  72s   replication-controller  Created pod: hello-rc-6tg65
ubuntu@k8s-master:~$
</Code>

You see that some pods are newer than other, these are the newly created ones :)

=====Rolling-Updates=====
TODO