=== Part 1: === 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 (Optional): If you want 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 Basic Docker Commands and Their Usage • ` docker --version` Usage: Displays the Docker version installed. Example: `docker --version` • `docker inf`o Usage: Provides detailed information about the Docker installation. Example:` docker info` • `docker pull ` Usage: Downloads a Docker image from Docker Hub. Example: `docker pull nginx` • `docker build -t : ` Usage: Builds a Docker image from a Dockerfile located at . Example: docker build -t myapp:latest . • ` docker images` Usage: Lists all available Docker images on the system. Example:` docker images` • `docker run ` 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 ` Usage: Stops a running container. Example: `docker stop my_container` • `docker rm ` Usage: Removes a stopped container. Example: `docker rm my_container` • ` docker rmi ` Usage: Removes a Docker image. Example: `docker rmi nginx` • `docker logs ` Usage: Displays logs from a running or stopped container. Example: `docker logs my_container` Troubleshooting Common Docker Container Issues • Container Fails to Start Check Logs: Use docker logs 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 | 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 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 to inspect a selected volume. Inspect Image: Use docker image inspect 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 to see some stats. • Image-Related Issues Pull Latest Image: Ensure you have the latest version of the image using docker pull . 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. === Part 2: === What is a Dockerfile? A Dockerfile is a script containing a set of instructions used by Docker to automate the process of building a new container image. It defines the environment inside the container, installs necessary software, sets up commands, and more. ==== Basic Structure of a Dockerfile ==== A Dockerfile consists of a series of instructions and arguments. Each instruction is an operation used to build the image, like installing a software package or copying files. The instruction is written in uppercase, followed by its arguments. Key Dockerfile Instructions FROM: Specifies the base image to start from. It's usually an OS or another application. Example: `FROM ubuntu:20.04` LABEL: Adds metadata to the image, like maintainer information. Example: `LABEL maintainer="name@example.com"` RUN: Executes commands in a new layer on top of the current image and commits the result. Example: `RUN apt-get update && apt-get install -y nginx` CMD: Provides defaults for the executing container. There can only be one CMD instruction in a Dockerfile. Example:` CMD ["nginx", "-g", "daemon off;"]` ENTRYPOINT: Configures the container to run as an executable. It's often used in combination with CMD. Example: `ENTRYPOINT ["nginx"]` COPY: Copies files or directories from the host machine to the container. Example: `COPY ./webapp /var/www/webapp` ADD: Similar to COPY, but can also handle URLs and tarball extraction. Example: `ADD https://example.com/app.tar.gz /app/` WORKDIR: Sets the working directory for any subsequent `RUN`, `CMD`, `ENTRYPOINT`,` COPY`, and `ADD` instructions. Example: `WORKDIR /app` EXPOSE: Informs Docker that the container listens on the specified network port at runtime. Example: `EXPOSE 80` ENV: Sets environment variables. Example: `ENV MY_VARIABLE=value` VOLUME: Creates a mount point for external storage or other containers. Example: `VOLUME /data` Let's create a Dockerfile for a basic web server using Nginx: First, create a folder called my-webserver and go inside it cd my-webserver Then create another folder inside that called website and a file called index.html within the folder website with any content of your choice. Create a file dockerfile with the following content within the my-webserver folder. # Use the official Nginx image as a base `FROM nginx:latest` # Set the maintainer label `LABEL maintainer="name@example.com"` # Copy static website files to the Nginx web directory `COPY ./website /usr/share/nginx/html` # Expose port 80 for the web server `EXPOSE 80` # Default command to run Nginx in the foreground `CMD ["nginx", "-g", "daemon off;"]` Building an Image from a Dockerfile To build a Docker image from your Dockerfile, navigate to the directory containing the Dockerfile and run: `docker build -t my-webserver:latest .` This command tells Docker to build an image using the Dockerfile in the current directory (.) and tag it as my-webserver:latest. Best Practices • Minimize Layers: Try to reduce the number of layers in your image to make it lightweight. For instance, chain commands using && in a single RUN instruction. • Use .dockerignore: Just like .gitignore, you can use .dockerignore to exclude files that aren't needed in the container. • Avoid Installing Unnecessary Packages: Only install the packages that are necessary to run your application. • Clean Up: Remove temporary files and caches to reduce image size. === Part 3: === What is Docker Compose? Docker Compose is a tool for defining and running multi-container Docker applications. With Compose, you can define a multi-container application in a single file, then spin up your application with a single command (docker-compose up). Key Concepts Services: Each container started by Docker Compose is a service. Services are defined in the docker-compose.yml file. Networks: By default, Docker Compose sets up a single network for your application. Each container for a service joins the default network and is discoverable via a hostname identical to the container name. Volumes: Volumes can be used to share files between the host and container or between containers. Basic docker-compose Commands • ` docker-compose up`: Starts up the services defined in the docker-compose.yml file. • ` docker-compose down`: Stops and removes all the containers defined in the docker-compose.yml file. • ` docker-compose ps`: Lists the services and their current state (running/stopped). • `docker-compose logs`: Shows the logs from the services. Deploying WordPress with Docker Compose Let's deploy a WordPress application using two containers: one for WordPress and another for the MySQL database. Create a docker-compose.yml file: version: '3' services: # Database Service db: image: mysql:5.7 volumes: - db_data:/var/lib/mysql environment: MYSQL_ROOT_PASSWORD: somewordpress MYSQL_DATABASE: wordpress MYSQL_USER: wordpress MYSQL_PASSWORD: wordpress # WordPress Service wordpress: depends_on: - db image: wordpress:latest ports: - "8080:80" environment: WORDPRESS_DB_HOST: db:3306 WORDPRESS_DB_USER: wordpress WORDPRESS_DB_PASSWORD: wordpress WORDPRESS_DB_NAME: wordpress volumes: - wordpress_data:/var/www/html volumes: db_data: {} wordpress_data: {} Start the WordPress and Database Containers: Navigate to the directory containing the docker-compose.yml file and run: docker-compose up -d This command will start the services in detached mode. Once the services are up, you can access the WordPress site by navigating to `http://:8080` from your browser. Stopping the Services: To stop the services, navigate to the same directory and run: `docker-compose down` Best Practices • Explicit Service Names: Give your services explicit names to make it clear what each service does. • Environment Variables: Use environment variables for sensitive information and configurations. • Service Dependencies: Use the depends_on option to ensure services start in the correct order. ==== Part 4: ==== Deploy any web app as per your wish and showcase its usage of it. You need to use more than one docker container eg: you can use three containers, one to run a web app and the others to run a database and other data storage respectively. You may use the docker hub to get any existing containers. What we evaluate is your ability to deploy the containers and bringing up a working web app.