Docker

Docker

A containerized software that helps to reproduce environments between systems

• No it works on my machine

Files involved:

• Dockerfile
• .dockerignore
• docker-compose.yml

Dockerfile

Used to orchestrate an image

1. The FROM line, tells docker how to initialize (FROM node: , FROM debian:)
2. WORKDIR, tells docker where to initiate commands
3. RUN, commands ran in terminal (apt-get, npm run install)
4. EXPOSE ports
5. CMD, used to START the container after building (CMD ["npm", "start"])
   • This is not the same as the run command although their both terminal commands
   • You can only have ONE CMD per dockerfile

Docker Compose

Orchestrates different docker containers (IE a frontend, backend, and database)

• “multi-container applications”, modularizes different parts and allows the to communicate
• Defined in docker-compose.yml

Best Practices

1. Base image matters ALOT (using lastest can be 1gb+). Instead, use minimal images
   • -alpine is purpose built for containers (node:22-alpine)
2. Cache layers! Do reproducible things FIRST. (ie copy package.json first then install only that, instead of copying the entire workdir at a time)