Packer "references unknown source" in a build block in CI

By Kaveh Alemi·Latchkey

A build block links to sources by name. If the sources = [...] list names a source that no source block defines, Packer cannot wire the build and fails at load.

What this error means

packer validate or build fails with "build references unknown source X" because the name in the build block does not match a declared source.

Error: Unknown source amazon-ebs.ubunto

  on build.pkr.hcl line 20, in build:
  20:   sources = ["source.amazon-ebs.ubunto"]

Known: [source.amazon-ebs.ubuntu]

Common causes

A typo in the source reference

The sources list names amazon-ebs.ubunto while the source block is amazon-ebs.ubuntu, so no match is found.

The source block is in a file not loaded

The source is defined in a file outside the directory Packer builds, so it is not part of the loaded config.

How to fix it

Match the source name exactly

1. Read the "Known:" list Packer prints.
2. Correct the sources entry to match the declared source.
3. Run packer validate to confirm the build links.

build {
  sources = ["source.amazon-ebs.ubuntu"]
}

Build the directory that holds all files

Point Packer at the directory containing every source and build file so all blocks load together.

packer build .

How to prevent it

• Keep source and build blocks in the same loaded directory.
• Copy source names to avoid typos in the build block.
• Run packer validate before build to catch broken links.

Frequently asked questions

Related guides

References

• Terraform documentation
• GitHub Actions documentation