Containers

When there is no Dockerfile

A service with no Dockerfile is either deployed some other way — a fat jar on a VM, a buildpack, Fly or Heroku building it for you — or not deployed yet. Both are fine, and neither is something to change while doing an unrelated task.

Ask before writing one. How the service is packaged and shipped is a platform decision with a team behind it, and a Dockerfile that appears in a feature branch will be reviewed by someone who did not expect it. When it is genuinely wanted, say what you would produce — the jlink multi-stage build below, roughly this size, this base image — and wait.

Two things worth writing whenever you do create one: a .dockerignore (without it the build context is the whole tree including build/ and .git, which is slow and leaks more than you think) and the make image / make image_run targets from the ktor-toolkit:makefile skill, so the image is buildable the same way by everyone.

What we are optimising, in order