From Sensitive Single-Pod Deployments to Replica Set Resilliancy

In a previous post, a k8s cluster manages a handful of objects:

5 pods, each 1 "service" in a "microservice" style application
4 services, allowing explicit connectivity between the pods
- 2 open-to-the-world services, webapps
- 2 internal-only data stores, postgres and redis

This style of deployment is great for illustrating one "simple" way of deploying apps with pods, services, and kubernetes - for me specifically using minukube and k8s in docker, due to my current M1 mac restrictions and some online suggestions!

From Sensitive Single-Pod Deployments to Replica Set Resilliancy

More Pods for Frontend Apps

Here, The frontend-facing apps (voting-app and result-app) will get replica-sets through deployments. Deployments will "manage" the replica sets of the pods.

Comparing Pod-Based Deployments to Deployment-Managed Deployemnts

In some ways, using kubernetes deployemnt objects is "easier" that pod definition files. Deployments at least have more features:

the deployment will "manage" pods with a bit more automation than manual pod management
the deployment config file can include the number of replica pods to manage
- when 1+ pod(s) "dies" in a deployment, it gets automagically re-created by k8s

The deployment of the pods and services is also a bit different between this deployment-managed approach and a single-od-deployment approach:

in a single-pod approach, each pod gets a definition file and a deploy command
in a deployment-managed approach each deployment gets a definition file and a deploy command
- the difference here is implicit in that each deployment can have many pods per single definition file!!

Config Directory Structure

/cfgs
  /deployments
    redis.yaml
    pg.yaml
    worker.yaml
    voting-app.yaml
    results-app.yaml

Deployment Files

Redis

apiVersion: apps/v1
kind: Deployment
metadata:
  name: redis-deploy
  labels:
    name: redis-deploy
    app: demo-voting-app
spec:
  # save resources on my laptop!
  replicas: 1
  selector:
    matchLabels:
      name: redis-pod
      app: demo-voting-app
  template:
    metadata:
      name: redis-pod
      labels:
        name: redis-pod
        app: demo-voting-app
    spec:
      containers:
        - name: redis
          image: redis
          ports:
            - containerPort: 6379

postgres

apiVersion: apps/v1
kind: Deployment
metadata:
  name: pg-deploy
  labels:
    name: pg-deploy
    app: demo-voting-app
spec:
  replicas: 1
  selector:
    matchLabels:
      name: pg-pod
      app: demo-voting-app
  template:
    metadata:
      name: pg-pod
      labels:
        name: pg-pod
        app: demo-voting-app
    spec:
      containers:
        - name: pg-box
          image: postgres
          ports:
            - containerPort: 5432
          env:
            - name: POSTGRES_USER
              value: "postgres"
            - name: POSTGRES_PASSWORD
              value: "postgres"
              # hmm... this....
            - name: POSTGRES_HOST_AUTH_METHOD
              value: trust

worker

apiVersion: apps/v1
kind: Deployment
metadata:
  name: worker-deploy
  labels:
    name: worker-deploy
    app: demo-voting-app
spec:
  replicas: 1
  selector:
    matchLabels:
      name: worker-pod
      app: demo-voting-app
  template:
    metadata:
      name: worker-pod
      labels:
        name: worker-pod
        app: demo-voting-app
    spec:
      containers:
        - name: worker-box
          image: kodekloud/examplevotingapp_worker:v1

results-app

apiVersion: v1
kind: Deployment
metadata:
  name: result-app-deploy
  labels:
    name: result-app-deploy
    app: demo-voting-app
spec:
  replicas: 1
  selector:
    matchLabels:
      name: result-app-pod
      app: demo-voting-app
  template:
    metadata:
      name: result-app-pod
      labels:
        name: result-app-pod
        app: demo-voting-app
    spec:
      containers:
        - name: result-app-box
          image: kodekloud/examplevotingapp_result:v1
          ports:
            - containerPort: 80

voting-app

apiVersion: apps/v1
kind: Deployment
metadata:
  name: voting-app-deploy
  labels:
    name: voting-app-deploy
    app: demo-voting-app
spec:
  # to save resources on my laptop!
  replicas: 1
  selector:
    matchLabels:
      # match the voting-app pod def file
      name: voting-app-pod
      app: demo-voting-app
  template:
    # metadata taken directly from pod def file
    metadata:
      name: voting-app-pod
      labels:
        name: voting-app-pod
        app: demo-voting-app
    spec:
      containers:
        - name: voting-app-box
          image: kodekloud/examplevotingapp_vote:v1
          ports:
            # app listens on port 80
            - containerPort: 80

Deploying the Deployments

Validate that no pods or services are running. If you happen to be following along from the previous article, "A Microservice K8s Demo", The previous article leaves pods & services running. delete them before running these.

The Voting App

Jakes-4:k8s Jake$ kubectl create -f cfgs/deployments/voting-app.yaml
deployment.apps/voting-app-deploy created
Jakes-4:k8s Jake$ kubectl create -f cfgs/services/voting-app.yaml
service/voting-service created

# check the deployment!
NAME                READY   UP-TO-DATE   AVAILABLE   AGE
voting-app-deploy   1/1     1            1           30s

Redis

Jakes-4:k8s Jake$ kubectl create -f cfgs/deployments/redis.yaml
deployment.apps/redis-deploy created
Jakes-4:k8s Jake$ kubectl create -f cfgs/services/redis.yaml
service/redis created

# check it
Jakes-4:k8s Jake$ kubectl get deployments
NAME                READY   UP-TO-DATE   AVAILABLE   AGE
redis-deploy        1/1     1            1           12s
voting-app-deploy   1/1     1            1           99s

Postgres

Jakes-4:k8s Jake$ kubectl create -f cfgs/deployments/pg.yaml
deployment.apps/pg-deploy created
Jakes-4:k8s Jake$ kubectl create -f cfgs/services/pg.yaml
service/db created
Jakes-4:k8s Jake$ kubectl get deployments
NAME                READY   UP-TO-DATE   AVAILABLE   AGE
pg-deploy           1/1     1            1           8s
redis-deploy        1/1     1            1           81s
voting-app-deploy   1/1     1            1           2m48s

worker

Jakes-4:k8s Jake$ kubectl create -f cfgs/deployments/worker.yaml
deployment.apps/worker-deploy created

# check em!
# NOTE: the worker has no service running - its a pod with no service :)
Jakes-4:k8s Jake$ kubectl get pods,svc
NAME                                     READY   STATUS    RESTARTS      AGE
pod/pg-deploy-66b86c6c96-d6hpx           1/1     Running   0             115s
pod/redis-deploy-7f878dfd46-dfct6        1/1     Running   0             3m8s
pod/voting-app-deploy-664d76547c-2mfgn   1/1     Running   0             4m35s
pod/worker-deploy-745ff6d7f-7t7sj        1/1     Running   2 (18s ago)   24s

NAME                     TYPE        CLUSTER-IP      EXTERNAL-IP   PORT(S)        AGE
service/db               ClusterIP   10.99.48.13     <none>        5432/TCP       110s
service/kubernetes       ClusterIP   10.96.0.1       <none>        443/TCP        13d
service/redis            ClusterIP   10.97.51.245    <none>        6379/TCP       3m2s
service/voting-service   NodePort    10.97.220.203   1.2.3.110     80:30005/TCP   4m24s

results app

do the same with the results config :)

Scaling Up Live!

One major benefit of deployments is that the deployment "object" will "manage" pods, like when pods crash or when pods get scaled...live!! zero down time!!!

Edit The Results App Config File

The deployment "watches" deployment config files & wiill adjust the deployed pods & services accordingly.
Here, the replicas will be edited in the result-app config file.

# Edit the result app deployment to have 1 replica instead of 3
kubectl edit deployment result-app-deploy --record

# the config will show in the terminal
# find the replicas line and edit to be 1 instead of the
# :wq! to exit

# check the deployment, see 1/1 instead of 3/3 for the result-app-deploy
Jakes-4:k8s Jake$ kubectl get deployments
NAME                READY   UP-TO-DATE   AVAILABLE   AGE
pg-deploy           1/1     1            1           25h
redis-deploy        1/1     1            1           25h
result-app-deploy   1/1     1            1           16m
voting-app-deploy   1/1     1            1           25h
worker-deploy       1/1     1            1           25h

A Diagram

Tags:

Kubernetes