1. JTI - Docker

Goals

This exercise aims to containerize an application using Docker and use this container for the application's development.

Prerequisites

This exercise is intended for use concurrently with the theory part in this module. Start watching the recordings and pause when you reach Step #4.

You can then follow along and code with us. We're using neo4j and Python, but you should be able to translate this to MongoDB and Node.js (or any other environment you choose).

Important: Do not proceed to Step #5! That is for the next step.

Ensure you have Docker Desktop installed on your computer.

1. Pick the application

You can pick any application you like, but we recommend using the example application "Just Task It featuring Logging".

Create an empty repository jti-docker-1 on GitLab (preferably under https://gitlab.lnu.se/2dv013/student/<your username>/part-2-microservices/).

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Notes

  • Ensure you have the necessary permissions to clone both repositories and perform the git pull command.
  • Be cautious when working with unrelated repository histories; review the changes to make sure everything is correctly merged.

Environment variables

You'll use the .env file for environment variables during development. Rename example.env to .env and populate it.

Example:

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Note: In the database connection string, use the DNS name "mongodb". It's crucial to use this name when creating the Docker container that houses MongoDB.

2. Docker

Follow the Theory and demos (Steps #1-#4).

Key Points to Remember

  • Create a Network

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  • Run MongoDB Container

    Start MongoDB detached on the created network.

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  • Create a Dockerfile

    Follow this guide for containerizing a Node.js app.

  • Development Mode Command

    Use the following command to start Just Task It in dev mode:

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  • Mounting Source Folder

    Mount your src folder to /usr/src/app/src in the container.

    • Unix-like systems: $(pwd)
    • Windows (Bash): $(pwd -W)
    • Windows (PowerShell): ${PWD}

  • Environment Variables

    Since .env is ignored, use --env-file when starting Docker.

Dockerfile Example

In a multi-stage Dockerfile, the base stage installs application dependencies separately from the code to optimize caching and build speed. The final stage creates a lightweight runtime environment by copying only necessary files, reducing image size and enhancing security.

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MongoDB Setup

  • MongoDB Container: It runs as a separate container. Use the docker run command to start it on the network.

  • Environment Variables: Define them in the Docker host before running docker compose up.

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This setup ensures that you have a fully containerized environment with MongoDB and your Node.js application ready to develop and test.

.dockerignore

Instead of copying all files into the container, use a .dockerignore file to choose the files you want to copy. This process is known as "allowlisting".

Example:

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Test the Docker container

Open your web browser and visit http://localhost:3000. The application should be up and running. You should now be able to modify files in the src folder on your local machine. nodemon in the container will detect these changes and restart the application. Refresh your browser to confirm that changes to the front page are visible.

Next step

Setting up networks manually, building containers, and running them can be complex, especially when you have multiple services and dependencies. To manage this complexity, the next step will introduce you to a tool called Docker Compose.

Proceed to the next step