7 Quick Steps for Managing Docker Containers on Debian VPS Servers

Docker has revolutionized the software development industry by making it possible to package applications into containers. This guide provides 7 quick steps for managing Docker containers on Debian VPS servers. It is designed for system administrators and developers who are familiar with basic Linux commands and concepts.

1. Introduction to Docker and Containers

Benefits of Using Docker

Docker simplifies the deployment of applications. Containers, which include all necessary executables, binary code, libraries, and configuration files, help create lightweight, secure environments. They ensure consistency across multiple development, testing, and production environments.

Docker vs. Virtual Machines

Unlike virtual machines (VMs) that require a full-blown operating system, Docker containers share the host OS system kernel and are therefore more resource-efficient.

2. Setting Up Debian VPS for Docker

Prerequisites

• A Debian VPS (Preferably Debian 10 or newer)
• A non-root user with sudo privileges (See: How to Add User to Sudoers in Debian VPS)

Installing Docker on Debian

1. Update Your System:

   sudo apt update
   sudo apt upgrade -y
   

2. Install Required Packages:

   sudo apt install apt-transport-https ca-certificates curl software-properties-common -y
   

3. Add Docker’s Official GPG Key:

   curl -fsSL https://download.docker.com/linux/debian/gpg | sudo apt-key add -
   

4. Set Up the Stable Repository:

   sudo add-apt-repository "deb [arch=amd64] https://download.docker.com/linux/debian $(lsb_release -cs) stable"
   

5. Install Docker Engine:

   sudo apt update
   sudo apt install docker-ce docker-ce-cli containerd.io -y
   

6. Verify Installation:

   sudo systemctl status docker
   

Adding User to the Docker Group

sudo usermod -aG docker ${USER}
su - ${USER}

3. Working with Docker Containers

Running Containers

docker run -d -p 80:80 docker/getting-started

This command downloads a test image and runs it in a detached mode.

Managing Container Lifecycles

• Start a container: docker start CONTAINER_ID
• Stop a container: docker stop CONTAINER_ID
• Remove a container: docker rm CONTAINER_ID

Accessing Running Containers

docker exec -it CONTAINER_ID /bin/bash

4. Docker Images

Managing Images

• List all images: docker images
• Remove an image: docker rmi IMAGE_ID

Building Images from a Dockerfile

1. Create a Dockerfile:

   # Use an official Python runtime as a parent image
   FROM python:3.7-slim
   
   # Set the working directory to /app
   WORKDIR /app
   
   # Copy the current directory contents into the container at /app
   ADD . /app
   
   # Install any needed packages specified in requirements.txt
   RUN pip install --trusted-host pypi.python.org -r requirements.txt
   
   # Make port 80 available to the world outside this container
   EXPOSE 80
   
   # Define environment variable
   ENV NAME World
   
   # Run app.py when the container launches
   CMD ["python", "app.py"]
   

2. Build the image:

   docker build -t my-python-app .
   

5. Networking and Communication

Port Mapping

docker run -p 6000:6379 redis

This command maps port 6379 inside the container to port 6000 on your Debian VPS.

Linking Containers

docker run -d --name redis redis
docker run -d --name myapp --link redis myapp

Using Docker Compose

1. Create a docker-compose.yml file:

   version: '3'
   services:
     web:
       build: .
       ports:
        - "5000:5000"
       volumes:
        - .:/code
       depends_on:
        - redis
     redis:
       image: "redis:alpine"
   

2. Run with Docker Compose:

   docker-compose up
   

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6. Advanced Docker Features

Docker Volumes for Persistent Storage

docker run -d \
  --name devtest \
  -v myvolume:/app \
  nginx:latest

Setting Up a Docker Swarm

1. Initialize the Swarm:

   docker swarm init
   

2. Add Nodes:

   docker swarm join --token SWMTKN-1-0xq4siwj5sargflkd6fs3zqr2z3caasciu9e8v3ttz3wimwxhw-8xw3zf6g0phkw8iwqrmnemrvk 192.168.99.100:2377
   

Best Practices for Security

• Use official images.
• Regularly update images.
• Minimize exposed ports.

7. Troubleshooting and Tips

Common Issues

• Docker service not starting: Ensure you have the correct permissions and the service is enabled.
• Containers not communicating: Check your firewall and network settings.

Performance Optimization

• Use lightweight images where possible due to their smaller footprint.
• Limit resources per container through Docker’s resource constraints capabilities.

8. Conclusion

Managing Docker containers on a Debian VPS is efficient and effective once you grasp the basics. Through this guide, you have learned how to install Docker, run containers, manage their lifecycles, handle images, establish network communications between containers, and utilize Docker’s advanced features. With these skills, you can maintain a robust, secure, and high-performance Docker environment on your Debian VPS.