Packer "Unknown builder type" in CI

By Daniel Zoghalchali·Latchkey

Packer could not resolve the builder named in a source block to any installed plugin. Since 1.7 the builders ship as external plugins, so an uninstalled plugin surfaces as an unknown type.

What this error means

packer build or validate fails with "1 error occurred: Unknown builder type: X" and lists only the built-in types (file, null) as known.

Error: 1 error occurred:
	* Unknown builder type: amazon-ebs

  known builder types: file, null

Common causes

The plugin providing the builder is not installed

For 1.7+, amazon-ebs, googlecompute, and similar live in plugins. Without packer init, only file and null are known.

A typo in the source block type

The source line names a builder that does not exist, for example amazon_ebs instead of amazon-ebs.

How to fix it

Install the plugin with packer init

1. Declare the plugin in required_plugins.
2. Run packer init before build so the builder type is registered.
3. Re-run build and confirm the type resolves.

packer init .
packer build .

Correct the builder name

Match the type exactly, for example source "amazon-ebs" "ubuntu", with hyphens not underscores.

source "amazon-ebs" "ubuntu" {
  region        = "us-east-1"
  instance_type = "t3.micro"
}

How to prevent it

• Run packer init before build for any 1.7+ template.
• Copy builder type names from plugin docs to avoid typos.
• Cache plugins so the builder stays registered across jobs.

Frequently asked questions

Related guides

References

• Terraform documentation
• GitHub Actions documentation