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Relative workdir 'app/src' can have unexpected results if the base image changes


When specifying WORKDIR in a build stage, you can use an absolute path, like /build, or a relative path, like ./build. Using a relative path means that the working directory is relative to whatever the previous working directory was. So if your base image uses /usr/local/foo as a working directory, and you specify a relative directory like WORKDIR build, the effective working directory becomes /usr/local/foo/build.

The WorkdirRelativePath build rule warns you if you use a WORKDIR with a relative path without first specifying an absolute path in the same Dockerfile. The rationale for this rule is that using a relative working directory for base image built externally is prone to breaking, since working directory may change upstream without warning, resulting in a completely different directory hierarchy for your build.


❌ Bad: this assumes that WORKDIR in the base image is / (if that changes upstream, the web stage is broken).

FROM nginx AS web
WORKDIR usr/share/nginx/html
COPY public .

✅ Good: a leading slash ensures that WORKDIR always ends up at the desired path.

FROM nginx AS web
WORKDIR /usr/share/nginx/html
COPY public .