Dockerfile Tip 1: Define a Base Layer

With the advent of the Multi Stage Dockerfile, it’s very common for people to very specific layers that do a single task; which often utilise the same “primary” base layer.

Example:

FROM elixir:1.8 AS deps

RUN mix deps.get

FROM elixir:1.8 AS compile

COPY --from=deps ...

RUN mix compile

This allows lengthy tasks to utilise the build cache and pass artefacts between layers, without rerunning the lengthy task. However, I often see this “primary” layer duplicated 4/6/10 times in a single Dockerfile; making maintenance cumbersome.

The Tip

Create an empty layer with your primary image:

FROM elixir:1.8 AS base

FROM base AS deps

# ...

FROM base AS compile

# ...

This reduces duplication and makes maintenance, and pull-requests, easier to review/manage/change.

Until next time :metal: