Day 25 - Kubernetes - Deployment

 k8s - Deployment - 2/27/2021

How do you deploy your application in prod env?

We have to deploy multiple web servers
- New applicaiton build comes in
- How do upgrade?
- You may not want to update all at once. One at a time - (rolling update)
- What if you encounter on one of the instance and you have to rollback?
- If you want to have multiple change on your env, say application version, scaling env, resource allocation etc, you don't want to apply all all changes immediately, for the command is running, but pause your env, make the changes to your env and resume the change are done together.

All of these can be done through deployment.
- Each container is encapsulated in POD.
- Multiple PODs are deployed using RS or RC.

Deployment comes on top of RS or RC which allows us to upgrade the underline instances flawlessly
- using rolling updates.
- undo changes
- pause/resume as required


How to create deployment?

- Create deployment definition file
- Content of the definition file is similar to rs.
- Only we change is kind: Deployment

# cat dep-def.yaml
apiVersion: apps/v1
kind: Deployment
metadata:
  name: myappDep
  labels:
    app: myapp
    type: front-end

spec:
  template:
    metadata:
      name: myapp-pod
      labels:
        app: myapp
        type: front-end
    spec:
      containers:
      - name: nginx-controller
        image: nginx

  replicas: 3
  selector:
    matchLabels:
      type: front-end

> kc create -f dep-def.yaml
> kc get deployments

Deployment automatically creates replicaSets
> kc get rs

you see the rs in the name of deployment

> kc get pods
you see the name of the pod with deployment.

Get all deployment, RS and POds
> kc get all


Visit the link for more detail
https://kubernetes.io/docs/reference/kubectl/conventions/

Create an nginx POD
# kc run nginx --image=nginx

Create POD manifest YAML file (-o yaml) don't create (--dry-run)
# kc run nginx --image=nginx --dry-run=client -o yaml

create deployment
# kc create deployment nginx --image=nginx

Create deployment def fine without creating it (--dry-run)
# kc create deployment mydep --image=nginx --dry-run=client -o yaml

generate with replicas
# kc create deployment mydep --image=nginx --replicas=3 --dry-run=client -o yaml > dep-def.yaml

# kc apply -f dep-def.yaml