1. Overview
When dealing with containerized applications, we might want to know what roles Docker Compose and Kubernetes play in this context.
In this tutorial, we'll discuss some of the most common use cases to see the difference between the two.
2. Docker Compose
Docker Compose is a command-line tool to run multiple Docker containers with a YAML template definition. We can build containers from existing images or a specific context.
We can add a version of the compose file format and at least one service. Optionally, we can add volumes and networks. Also, we can define dependencies and environment variables.
2.1. Docker Compose Template
Let's create a docker-compose.yml file for an API connecting to a PostgreSQL database:
version: '3.8'
services:
db:
image: postgres:latest
restart: always
environment:
- POSTGRES_USER=postgres
- POSTGRES_PASSWORD=postgres
ports:
- '5432:5432'
volumes:
- db:/var/lib/postgresql/data
networks:
- mynet
api:
container_name: my-api
build:
context: ./
image: my-api
depends_on:
- db
networks:
- mynet
ports:
- 8080:8080
environment:
DB_HOST: db
DB_PORT: 5432
DB_USER: postgres
DB_PASSWORD: postgres
DB_NAME: postgres
networks:
mynet:
driver: bridge
volumes:
db:
driver: local
Finally, we can start working locally or in production by running:
docker-compose up
2.2. Docker Compose Common Use Cases
We commonly use Docker Compose to create a microservice infrastructure environment that links different services over a network.
In addition, Docker Compose is widely used to create and destroy isolated testing environments for our test suites.
Moreover, if we are interested in scalability, we can look at Docker Swarm — a project created by Docker to work at the orchestration level like Kubernetes.
However, compared to Kubernetes, Docker Swarm has limited offerings.
3. Kubernetes
With Kubernetes (also referred to as K8s), we automate the deployment and management of applications in a containerized and clustered environment. Google's initial work on K8s went from open-source to a donation to the Linux Foundation and eventually as a seed technology to start the Cloud Native Computing Foundation (CNCF).
In the container era, Kubernetes got significant attention to such an extent that it's now the most popular distributed system orchestrator.
A complete API is available to describe the specifications and status of Kubernetes' Objects. It also allows integration with third-party software.
In Kubernetes, different components are part of a cluster that consists of a set of worker machines called Nodes. The Nodes are running our containerized applications inside Pods.
Kubernetes is all about managing artifacts deployed in Pods on virtual machines or Nodes. The Nodes and the containers they run are all grouped as a cluster, and each container has endpoints, DNS, storage, and scalability.
Pods are nonpermanent resources. For example, a Deployment can create and destroy them dynamically. Usually, we can expose applications as Services to always be available at the same endpoint.
3.1. Kubernetes Template
Kubernetes provides a declarative or imperative approach, so we can use templates to create, update, delete or even scale Objects. As an example, let's define a template for a Deployment:
-- Postgres Database
apiVersion: apps/v1
kind: Deployment
metadata:
name: postgresql
namespace: Database
spec:
selector:
matchLabels:
app: postgresql
replicas: 1
template:
metadata:
labels:
app: postgresql
spec:
containers:
- name: postgresql
image: postgresql:latest
ports:
- name: tcp
containerPort: 5432
env:
- name: POSTGRES_USER
value: postgres
- name: POSTGRES_PASSWORD
value: postgres
- name: POSTGRES_DB
value: postgres
volumeMounts:
- mountPath: /var/lib/postgresql/data
name: postgredb
volumes:
- name: postgredb
persistentVolumeClaim:
claimName: postgres-data
-- My Api
apiVersion: apps/v1
kind: Deployment
metadata:
name: my-api
namespace: Api
spec:
selector:
matchLabels:
app: my-api
replicas: 1
template:
metadata:
labels:
app: my-api
spec:
containers:
- name: my-api
image: my-api:latest
ports:
- containerPort: 8080
name: "http"
volumeMounts:
- mountPath: "/app"
name: my-app-storage
env:
- name: POSTGRES_DB
value: postgres
- name: POSTGRES_USER
value: postgres
- name: POSTGRES_PASSWORD
value: password
resources:
limits:
memory: 2Gi
cpu: "1"
volumes:
- name: my-app-storage
persistentVolumeClaim:
claimName: my-app-data
We can then use objects over the network with the kubectl command line.
3.2. Kubernetes and Cloud Providers
Kubernetes is not Infrastructure-as-Code (IaC) itself. However, it integrates with cloud providers' container services — for example, ECS or EKS by Amazon, GKE by Google, and OpenShift by RedHat.
Or we can use it, for instance, with tools like Helm.
We do commonly see Kubernetes in public cloud infrastructures. However, we can set up Minikube or a local Kubeadm cluster.
Also approved by CNCF, we can checkout K3s, a lightweight version of K8s.
4. Differences Between Kubernetes and Docker Compose
While Docker Compose is about creating and starting one or multiple containers, Kubernetes serves more as a platform to create a network where we can orchestrate containers.
Kubernetes has been able to facilitate many crucial problems in applications management:
- Resource optimization
- Self-healing of containers
- Downtimes during applications redeployment
- Auto-scaling
Finally, Kubernetes takes multiple isolated containers to a stage where resources are always available with the potential optimal distribution.
However, when it comes to development, Docker Compose can configure all the application’s service dependencies to get started with, for example, our automated tests. So, it's a powerful tool for local development.
5. Conclusion
In this article, we've seen the difference between Docker Compose and Kubernetes. Docker Compose can help when we need to define and run multi-container Docker applications.
Kubernetes is a powerful yet complex framework for managing containerized applications in a clustered environment.
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