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 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

Troubleshooting Common Docker Container Issues

• 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.

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@…"

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@…"

# 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://<Floating_IP>: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.