kubernetes - Deployment

We can always create a Replication controller along with a pods, so that it will take care of how many pods it should keep running. What if we need to do a rolling update to the container running? . what if i have new changes and want to push them to container ?

Deployment is the one which provide these. A Deployment is a supervisor for pods and replica

sets giving you a fine grained control over how and when a new pod version is rolled out as well

as rolled back to the previous state.

The main purpose is to keep a set of identical pods running and update them in a controlled

way, performing a rolling update by default.

Create a basic deployment as,

[root@manja17-I13330 kubenetes-config]# cat basic-deployment.yml

apiVersion: apps/v1beta1

kind: Deployment

metadata:

 name: test-service-deploy

spec:

 replicas: 2

 template:

   metadata:

     labels:

       app: test-service

   spec:

     containers:

     - name: test-ser

       image: docker.io/jagadesh1982/testing-service

       ports:

       - containerPort: 9876

       env:

       - name: VERSION

         value: "0.5"

We are actually creating a basic deployment for the testing-service. We also passed and

environment value called “Version” with a value “0.5”.

Check if the deployments are available,

[root@manja17-I13330 kube-testing]# kubectl get deployments

NAME                   DESIRED CURRENT UP-TO-DATE   AVAILABLE AGE

test-service-deploy   2 2 2            0 6s

Now if we see that we have 2 pods created automatically.

[root@manja17-I13330 kube-testing]# kubectl get pods

NAME                                                 READY STATUS RESTARTS AGE

test-service-deploy-85c8787b6f-6msvv   1/1 Running 0 13s

test-service-deploy-85c8787b6f-nc9kz    1/1 Running 0 13s

Now lets take a POD ,get the IP and see if we can access the application

[root@manja17-I13330 kube-testing]# kubectl describe pod test-service-deploy-85c8787b6f-6msvv | grep IP

IP:             10.47.0.1

[root@manja17-I13330 kube-testing]# curl 10.47.0.1:9876/info

{"host": "10.47.0.1:9876", "version": "0.5", "from": "10.32.0.1"}

If we see that we have accessed the application and we can see that the version is 0.5 in here.

Now if we want to make any modifications ,we can edit the deploy file using,

[root@manja17-I13330 kube-testing]# kubectl edit deploy/test-service-deploy

deployment.extensions "test-service-deploy" edited

I made the replicas from 2 to 3 and saved the changes. I also changed the env value from “0.5”

to “2”. This way iam actually pushing new changes to my container code.
[root@manja17-I13330 kube-testing]# kubectl get deploy

NAME                      DESIRED CURRENT UP-TO-DATE   AVAILABLE AGE

test-service-deploy   2 3          1 2      5m

Now if we see the pods we can see,

[root@manja17-I13330 kube-testing]# kubectl get pods

NAME                                                READY STATUS RESTARTS AGE

test-service-deploy-5fdf56d98c-hvsjn   1/1 Terminating 0 2m

test-service-deploy-5fdf56d98c-sglr8   1/1 Terminating 0 2m

test-service-deploy-98bf447c8-c7ct6    1/1 Running 0 14s

test-service-deploy-98bf447c8-lh7s6    1/1 Running 0 8s

Get the IP address for one of the POD and access the application as,

[root@manja17-I13330 kube-testing]# kubectl describe pod test-service-deploy-98bf447c8-c7ct6 | grep IP

IP:             10.44.0.1

[root@manja17-I13330 kube-testing]# curl http://10.44.0.1:9876/info

{"host": "10.44.0.1:9876", "version": "2", "from": "10.32.0.1"}

We can see that the application is now pointing to the version 2 as we passed in our

environment variables. Beside providing a single point for your whole deployment , it also
provides some more features like

[root@manja17-I13330 kube-testing]# kubectl rollout history deploy/test-service-deploy

deployments "test-service-deploy"

REVISION  CHANGE-CAUSE

1          <none>

2          <none>

3          <none>

We can see the rollout version of the deployment. We can also check the progress of the deployment using

[root@manja17-I13330 kube-testing]# kubectl rollout status deploy/test-service-deploy

deployment "test-service-deploy" successfully rolled out

We can also rollback to the old version using,

[root@manja17-I13330 kube-testing]# kubectl rollout undo deploy/test-service-deploy --to-revision=1

deployment.apps "test-service-deploy"

And once the rollback is done, we can access the application and see the application is pointing

to the old version as below.

[root@manja17-I13330 kube-testing]# curl 10.47.0.3:9876/info

{"host": "10.47.0.3:9876", "version": "0.5", "from": "10.32.0.1"}

More to Come , Happy learning :-)