A Practical Guide to Kubernetes/

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Comparison with Docker Swarm

Comparison with Docker Swarm

Compare Kubernetes Deployments with Docker Swarm stacks.

We'll cover the following...

Kubernetes Deployments compared to Docker Swarm stacks

If you have already used Docker Swarm, the logic behind Kubernetes Deployments should be familiar. Both serve the same purpose and can be used to deploy new applications or update those that are already running inside a cluster. In both cases, we can easily deploy new releases without any downtime (when application architecture permits that).

Comparing definitions

Let’s look at the way we define objects in both Kubernetes and Docker Swarm.

Kubernetes

An example of a Kubernetes Deployment and Service definition is as follows:

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apiVersion: apps/v1
kind: Deployment
metadata:
  name: go-demo-2-db
spec:
  selector:
    matchLabels:
      type: db
      service: go-demo-2
  strategy:
    type: Recreate
  template:
    metadata:
      labels:
        type: db
        service: go-demo-2
        vendor: MongoLabs
    spec:
      containers:
      - name: db
        image: mongo:3.3
        ports:
        - containerPort: 27017
---
apiVersion: v1
kind: Service
metadata:
  name: go-demo-2-db
spec:
  ports:
  - port: 27017
  selector:
    type: db
    service: go-demo-2
---
apiVersion: apps/v1beta2
kind: Deployment
metadata:
  name: go-demo-2-api
spec:
  replicas: 3
  selector:
    matchLabels:
      type: api
      service: go-demo-2
  template:
    metadata:
      labels:
        type: api
        service: go-demo-2
        language: go
    spec:
      containers:
      - name: api
        image: vfarcic/go-demo-2
        env:
        - name: DB
          value: go-demo-2-db
        readinessProbe:
          httpGet:
            path: /demo/hello
            port: 8080
          periodSeconds: 1
        livenessProbe:
          httpGet:
            path: /demo/hello
            port: 8080
---
apiVersion: v1
kind: Service
metadata:
  name: go-demo-2-api
spec:
  type: NodePort
  ports:
  - port: 8080
  selector:
    type: api
    service: go-demo-2

Docker Swarm

An equivalent Docker Swarm stack definition is as follows:

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version: "3"
services:
  api:
    image: vfarcic/go-demo-2
    environment:
      - DB=db
    ports:
      - 8080
    deploy:
      replicas: 3
  db:
    image: mongo:3.3

Both definitions provide, more or less, the same functionality.

It is evident that a Kubernetes Deployment requires a much longer definition with more complex syntax. It is worth noting that Swarm’s equivalent to readinessProbe and livenessProbe is not present in the stack because it is defined as a HEALTHCHECK inside the Dockerfile. Still, even if we remove them, a Kubernetes Deployment remains longer and more complicated. ...