Docker .dockerignore Silently Excludes a Needed File in CI

A .dockerignore pattern is broader than intended and removes a file the Dockerfile copies. The build context never includes it, so a later COPY fails or the image is built without it.

What this error means

A build fails with "not found" / "no source files" for a file that clearly exists in the repo - or the image builds but is missing a file at runtime. The file is present on disk but excluded from the context by .dockerignore.

docker build output

ERROR: failed to solve: failed to compute cache key: "/app/.env.production": not found
# .dockerignore contains a broad "*.env*" or ".env*" that drops .env.production

Common causes

An over-broad ignore pattern

A wildcard like *, .env*, or config* matches more than intended and removes a file the build relies on.

A negation (!) rule in the wrong order

.dockerignore evaluates patterns in order; a re-include (!keep.me) placed before a broader exclude is overridden, so the file stays excluded.

A directory excluded along with a needed child

Ignoring a whole directory (build/) also drops a file inside it the Dockerfile copies.

How to fix it

Check what the ignore file matches

Grep the pattern and re-include the needed file with a negation after the exclude.

.dockerignore

grep -nE 'env|config|build' .dockerignore
# re-include after the broad exclude:
# *.env*
# !.env.production

Narrow the pattern

Replace broad wildcards with specific paths.
Order negation (!) rules after the excludes they override.
Verify the file is in the context by inspecting a built image or using a debug COPY.

How to prevent it

Keep .dockerignore patterns specific, not broad wildcards.
Place !-negation re-includes after the matching exclude.
Review .dockerignore when adding files the Dockerfile must copy.