LKNOG Wiki

'Installing Docker on Ubuntu Server'

1. Update Your System: Ensure your system package database is up-to-date.

`sudo apt update`

`sudo apt upgrade`

2. Install Docker: Install Docker using the convenience script provided by Docker.

`curl -fsSL https://get.docker.com -o get-docker.sh`

`sudo sh get-docker.sh`

3. Add User to Docker Group: to run Docker commands without sudo, add your user to the docker group.

`sudo usermod -aG docker ${USER}`

Log out and log back in for the group changes to take effect.

4. Start and Enable Docker: Ensure Docker starts on boot.

` sudo systemctl enable docker`

` sudo systemctl start docker`

5. Verify Docker Installation: Check the Docker version to ensure it's installed correctly.

` docker –version`

6. Deploying a Sample Web Application using Docker

6.1 Pull a Sample Web Application Image: For this guide, we'll use a simple HTTP server image from Docker Hub.

` docker pull httpd`

6.2 Run the Web Application: Start a container using the httpd image. This will run the web server on port 8080.

` docker run -d -p 8080:80 –name sample-webapp httpd`

6.3 Access the Web Application: If you're accessing the server locally, open a web browser and navigate to: (Since you are connected via SSH lets install a text-based web browser lynx.)

`sudo apt-get install lynx`

`lynx http://localhost:8080`

6.4 Stop and Remove the Web Application (Optional): When you're done testing the web application, you can stop and remove the container.

` docker stop sample-webapp`

` docker rm sample-webapp`

Extra Ref:

[https://linuxhint.com/best_linux_text_based_browsers/]

[https://romanzolotarev.com/ssh.html]

• ` docker –version`

      Usage: Displays the Docker version installed.
      Example: `docker --version`

• `docker info`

      Usage: Provides detailed information about the Docker installation.
      Example:` docker info`

• `docker pull <image_name>`

      Usage: Downloads a Docker image from Docker Hub.
      Example: `docker pull nginx`

• `docker build -t <image_name>:<tag> <path>`

      Usage: Builds a Docker image from a Dockerfile located at <path>.
      Example: docker build -t myapp:latest .

• ` docker images`

      Usage: Lists all available Docker images on the system.
      Example:` docker images`

• `docker run <options> <image_name>`

      Usage: Creates and starts a container from a Docker image.
      Example: `docker run -d -p 80:80 nginx`

• `docker ps`

      Usage: Lists running containers.
      Example:` docker ps`

• ` docker ps -a`

      Usage: Lists all containers, including stopped ones.
      Example: `docker ps -a`

• `docker stop <container_id/container_name>`

      Usage: Stops a running container.
      Example: `docker stop my_container`

• `docker rm <container_id/container_name>`

      Usage: Removes a stopped container.
      Example: `docker rm my_container`

• ` docker rmi <image_name>`

      Usage: Removes a Docker image.
      Example: `docker rmi nginx`

• `docker logs <container_id/container_name>`

      Usage: Displays logs from a running or stopped container.
      Example: `docker logs my_container`

• Container Fails to Start

      Check Logs: Use `docker logs <container_name>` to check for any error messages.
     
       Inspect Configuration: Ensure that the Docker run command has the correct parameters, such as port mappings and volume mounts.

• Networking Issues

      Check IP Address: Use `docker inspect <container_name> | grep IPAddress` to find the container's IP address.
      
      Check Port Bindings: Ensure that the ports inside the container are correctly mapped to the host using the -p option.
      You may use `docker port <container_name>` to further check the port mapping.

• File or Directory Not Found in Container

      Check Volumes: Ensure that directories or files from the host are correctly mounted into the container using the -v option.
      You may use `docker volume ls` to list all volumes mapped and `docker volume inspect  <volume_name>` to inspect a selected volume.
      Inspect Image: Use `docker image inspect <image_name>` to see the image's layers and ensure the required files are present.

• Container Performance Issues

      Check Resources: Containers might face performance issues if they're not allocated enough resources. Use `docker stats` to check the resource usage of running containers.
      Limit Resources: When running a container, you can use flags like `--cpus` and `--memory` to limit its resources.
      You can use `docker top <container_name>` to see some stats.

• Image-Related Issues

      Pull Latest Image: Ensure you have the latest version of the image using `docker pull <image_name>`.
      Check Dockerfile: If you're building your own image, ensure that the Dockerfile has the correct instructions.

• Permission Issues

      User Mappings: If a containerized application can't access certain files, it might be a user permission issue. Ensure that the user inside the container has the necessary permissions.
      Use `--user` Flag: When running a container, you can specify which user the container should run as using the --user flag.