Deployment Basics

May 5, 2024 · 2 min read · k8s kubernetes ·

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(this post is part of the material I cover in my devops course)

The main power of kubernetes is running things at scale.
Deployments are meant to run multiple pods, on multiple nodes.

About Deployments

A kuberneteis deployment is a kubernetes object that is meant to define and run pods at scale.
It contains another kubernetes object called ReplicaSet which is responsible on running multiple pods as part of a deployment.
The deployment can rollout versions, by creating a new ReplicaSet, and then gradually creating new pods in it, while terminating pods in the old ReplicaSet.
If your ReplicaSet is part of a Deployment, you should not try to manage it directly.

Creating a basic Deployment

A deployment YAML definition contains a template of a pod.
It means that all of the pods that are going to be created will be based on this template.
If you name your pod (inside the template)
Here's an example:

 1apiVersion: apps/v1
 2kind: Deployment
 3metadata:
 4  name: my-deployment
 5spec:
 6  replicas: 3
 7  selector:
 8    matchLabels:
 9      app: my-deployment
10  template:
11    metadata:
12      labels:
13        app: my-deployment
14    spec:
15      containers:
16      - name: nginx
17        image: nginx:1.19.1
18        ports:
19        - containerPort: 80

Here's the creation of the deployment:

 1$> 
 2$> kubectl apply -f my-deployment.yaml 
 3deployment.apps/my-deployment created
 4$> kubectl get deployments
 5NAME            READY   UP-TO-DATE   AVAILABLE   AGE
 6my-deployment   3/3     3            3           9s
 7$> kubectl get replicaset
 8NAME                      DESIRED   CURRENT   READY   AGE
 9my-deployment-979fbc74d   3         3         3       21s
10$> kubectl get pods -o wide
11NAME                            READY   STATUS    RESTARTS   AGE   IP           NODE       NOMINATED NODE   READINESS GATES
12my-deployment-979fbc74d-5ljk8   1/1     Running   0          28s   10.244.3.5   five-m04   <none>           <none>
13my-deployment-979fbc74d-86lhp   1/1     Running   0          28s   10.244.2.6   five-m03   <none>           <none>
14my-deployment-979fbc74d-kbmjl   1/1     Running   0          28s   10.244.4.5   five-m05   <none>           <none>
15$>

You can edit a deployment directly. You'll get the look and feel of the vi editor.
Try to change the number of replicas:

1kubectl edit deployments my-deployment

You can also scale your deployment directly by using the kubectl scale command:

1kubectl scale deployment.v1.apps/my-deployment --replicas=2