Lab VMs Setup

In our lab sessions we are assigning some IP ranges for each of you. Please refer to the IP allocation table here.

First for your computer assign the IP address given as Host Machine. For this workshop we need to create 3 VMs in total. VMs are named as Master Node, Worker Node 1 and Worker Node 2. Accordingly we have given the relevant IP addresses for those as well in the table. But for this Lab session we only need a single a VM. Later you may create other 2 VMs.

Let's create a VM and give it the IP address allocated for Master Node.For this we are going to use Oracle Virtual Box 7.0 latest. If you haven't installed it on your computer download and install it.Install Virtual Box software with default settings, make sure you have enabled virtualization support from your host machine BIOS.

For all 3 VMs, we are going to Ubuntu 22.04 latest as the Operating System. For the Lab we are providing with a you a preinstalled Virtual Appliance file and you can download it from this ​link.

Import downloaded virtual appliance file (OVA file) into Oracle virtual box from File > Import Appliance.

While importing make sure to select Generate new MAC addresses for all Network Adapters from MAC Address Policy. Also you may change the field Name. For this Lab we recommend to have 4GB RAM and 4 CPU cores. You may change fields accordingly. Click finish to import the appliance.

Select the VM from left panel on Virtual box, right click and open Settings. Go to Network menu and on Adapter 1 choose Attached to be Bridged Adapter, then select the name of the network adapter currently you are connecting to the lab network.

Then start the VM using Green arrow button.

Once the VM is started login to the VM using below credentials.

username : user password : Learn2023

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: 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@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://<MASTER_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.