lightbulbBook reference: Beyond the books. Original notes kept below; rewrite them in your own words.
1.1.1 Docker
A Docker image is a filesystem snapshot plus a start command. A container is a running instance of that image.
Why it matters
“Works on my machine” dies when the image is the machine. CI, staging, and prod run the same bits.
How it is used
Write a small Dockerfile (slim base, non-root user, one process). Tag images by git SHA. Do not bake secrets into the image — inject them at runtime.