Every few weeks where I don’t touch Docker I tend to forget the basics:

Docker:

• Why use docker: so that with the same instructions (dockerfile), you will always get the same result in any environment.

Container vs Host:

• Instead of running different processes in OS directly, we run them as “containers” inside docker engine
• Each container is a service run within docker
• Host is your own computer’s OS, aka “outside of containers”

Docker compose:

• A way to define and run multiple containers
• Can specify dependencies between them

Dockerignore:

• .dockerignore file only applies to the building of image process, e.g., when doing ADD and COPY of folders
• To ignore a directory when COPYing, use the syntax **/dir

Why COPY?

• Why use COPY, when files are going to be synced between host and container anyway?
• COPY is only to make sure that a file exists to be used “in the build context”, for example, copy package.json before executing npm i in Dockerfile

Up and logs:

• docker-compose up
• docker-compose logs --follow service-name

EXEC vs RUN:

• EXEC reuses existing containers
• RUN creates new ones

EXPOSE vs PORTS:

• EXPOSE is only accessible within containers
• PORTS can be accessed on hosts