Diagnose: Cloud Run functions build failed on deploy

TL;DR

Fix: - Entry point mismatch: correct the flag or the export name so they match. - Runtime: move to a supported runtime and retest locally first. - Bloated source: check.gcloudignore excludes what should be excluded; huge uploads time out or pick up wrong files. - Dependency errors: pin versions in the manifest; unpinned installs break when upstream releases. Do not redeploy unchanged source hoping the build "recovers".

When to use

You are seeing this: Symptom: gcloud functions deploy fails with "Build failed" and a buildpacks error. Use this skill when you run into "Diagnose: Cloud Run functions build failed on deploy".

When not to use

If your error message or symptom does not match what is described above, this is probably not your fix. Search for your exact error text instead of forcing this one to fit.

Versions

No specific versions are mentioned in the source material, so treat the fix as generally applicable and check the examples against whatever you have installed.

Symptom: gcloud functions deploy fails with "Build failed" and a buildpacks error. The function never gets a revision.

Cause: the build step could not turn your source into a runnable container. Almost always one of: entry point mismatch, unsupported runtime, or source packaging problems.

Confirm:

1. Read the build logs fully: gcloud functions logs read or the Cloud Build log link in the error. The actual error is usually lines up from the bottom, not the summary line.
2. Entry point: does --entry-point exactly match the exported function name in your code? Case-sensitive. This is the top cause.
3. Runtime: is --runtime still supported? Old runtimes are decommissioned on a schedule; a deploy that worked six months ago can fail today on runtime alone.
4. Source dir: is --source pointing at the right directory? Does it contain the dependency manifest (package.json, requirements.txt, go.mod)? A missing manifest gives dependency-resolution failures.

Fix:

• Entry point mismatch: correct the flag or the export name so they match.
• Runtime: move to a supported runtime and retest locally first.
• Bloated source: check .gcloudignore excludes what should be excluded; huge uploads time out or pick up wrong files.
• Dependency errors: pin versions in the manifest; unpinned installs break when upstream releases.

Do not redeploy unchanged source hoping the build "recovers". Builds are deterministic; the same input fails the same way.

Verify: the build log shows a successful build and push, then the function revision becomes active and the trigger works.

Verified 2026-09-26 on the functions deploy docs: buildpacks-based build from --source, entry-point requirement, runtime support lifecycle. Runtime decommissioning is documented and ongoing (e.g. Node 18).