COPY failed: no source files were found

TL;DR: The COPY source pattern matches nothing in the build context. Check that the files exist relative to the build context root (not relative to the Dockerfile), that a .dockerignore is not excluding them, and that the pattern spelling matches. Nine times out of ten the build context is a different directory than you think, or .dockerignore swallowed the file.

The error

COPY failed: no source files were found

Fix it

1. Check what is actually in the build context. List the directory you pass to docker build (the PATH argument, often .):

ls in that directory, or docker build with the right context. Expected: the files you want to COPY are present there.

1. Inspect .dockerignore in the context root:

cat .dockerignore Expected: no rule excluding your files. Watch for broad rules like * or *.log with too few ! exceptions.

1. Fix the Dockerfile path or the build invocation, whichever is wrong:

• If files are elsewhere: docker build -f path/to/Dockerfile /correct/context/dir
• If the pattern is wrong: COPY paths are relative to context root, so COPY app/src /app needs app/src under the context, not under the Dockerfile dir.

1. Rebuild.

When this applies

• COPY/ADD with a glob or path that matches zero files
• Builds run from CI where the checkout directory differs from local

When this does NOT apply

• Error names the file and mentions .dockerignore explicitly (that is the ADD variant; same family, adjacent fix)
• "failed to read dockerfile" (the Dockerfile itself is missing from context)
• Permission errors during COPY (different failure)

Versions

All Docker Engine versions, classic builder and BuildKit. BuildKit phrases it identically.

Why it happens

COPY sources resolve against the build context, not the Dockerfile location. Running docker build -f docker/Dockerfile . with COPY src /app looks for ./src, not docker/src. A second classic is .dockerignore excluding the file, which removes it from the context before COPY runs, so the pattern matches nothing.

Edge cases

• Trailing-slash semantics: COPY src/ /app/ copies contents; COPY src /app copies the dir. Both fail the same way when src is missing.
• Symlinks pointing outside the context are not followed; COPY sees nothing.
• Windows line endings in .dockerignore can silently break exception rules.