UndefinedArgInFrom#

Output#

FROM argument 'VARIANT' is not declared

Description#

This rule warns for cases where you're consuming an undefined build argument in FROM instructions.

Interpolating build arguments in FROM instructions can be a good way to add flexibility to your build, and lets you pass arguments that overriding the base image of a stage. For example, you might use a build argument to specify the image tag:

ARG ALPINE_VERSION=3.20

FROM alpine:${ALPINE_VERSION}

This makes it possible to run the build with a different alpine version by specifying a build argument:

$ docker buildx build --build-arg ALPINE_VERSION=edge .

This check also tries to detect and warn when a FROM instruction reference miss-spelled built-in build arguments, like BUILDPLATFORM.

Examples#

❌ Bad: the VARIANT build argument is undefined.

FROM node:22${VARIANT} AS jsbuilder

✅ Good: the VARIANT build argument is defined.

ARG VARIANT="-alpine3.20"
FROM node:22${VARIANT} AS jsbuilder