---
description: |
  The `post-processor` block defines post-processor behavior after a `packer build` command. Learn how to configure `post-processor` blocks in your Packer templates. 
page_title: post-processor block reference
---

# `post-processor` block

This topic provides reference information about the `post-processor` block. 

## Description

The `post-processor` block defines how a post-processor is configured.

```hcl
# builds.pkr.hcl
build {
  # ... build image
  post-processor "checksum" { # checksum image
    checksum_types = [ "md5", "sha512" ] # checksum the artifact
    keep_input_artifact = true           # keep the artifact
  }

  post-processor "amazon-import" { # upload image to amazon
  }
}
```

Each `post-processor` runs after each defined build. A post-processor takes the
`Artifact` from a build. Post-processors are optional, and they can be used to
upload artifacts, re-package, or more. The list of available post-processors
can be found in the [post-processors](/packer/docs/post-processors) section.

A `post-processor` can also take the `Artifact` from another post-processor
when it is defined in a [`post-processors`
block](/packer/docs/templates/hcl_templates/blocks/build/post-processor) list, that is a list of
chained post processors.

-> Note: The input 'artifact' received by a post-processor will be automatically
deleted by default.

# Keep an input artifact

To prevent an input artifact from being deleted, you can set the
`keep_input_artifact` field to true to make Packer keep both artifacts. For
example if we want to checksum an artifact and keep the artifact:

```hcl
# builds.pkr.hcl
build {
  # ...
  post-processor "checksum" {
    checksum_types = [ "md5", "sha512" ]
    keep_input_artifact = true
  }
}
```

# Run on Specific Builds

You can use the `only` or `except` configurations to run a post-processor only
with specific sources. These two configurations do what you expect: `only` will
only run the post-processor on the specified sources and `except` will run the
post-processor on anything other than the specified sources.

An example of `only` being used is shown below, but the usage of `except` is
effectively the same:

```hcl
# builds.pkr.hcl
build {
  # ...
  post-processor "checksum" {
    checksum_types = [ "md5", "sha512" ]
    keep_input_artifact = true
    only = ["amazon-ebs.example"]
  }
}
```

The values within `only` or `except` are _source names_, not builder types.

If you want to exclude certain post-processors when running `packer build`
from the command line, you can do so:

`packer build --except=checksum mytemplate.pkr.hcl` will not run the checksum
post-processor. This command line exclusion works by referencing post-processor
_name_. By default, the post-processor is named after is its type, as
demonstrated above in the `checksum` example. You can make a post-processor's
name unique by adding a "name" field to each post-processor block.

While the `-except` flag can be used to filter out post-processors on the
command line, the `-only` flag does not work for post-processors. If you wish
to only run a post-processor for a given source build  you must use the
`only=[source]` syntax inside of your hcl templates, as described above.


## Build Contextual Variables

Packer allows to access connection information and basic instance state
information from a post-processor. These information are stored in the `build`
variable. Check out the [Contextual
Variables](/packer/docs/templates/hcl_templates/contextual-variables) documentation to learn more
about and see some examples of how to use them.

### Related

- The [`post-processors` block](/packer/docs/templates/hcl_templates/blocks/build/post-processors)
  allows to define one or more chain of `post-processor`s that will take the
  output from the build and provision steps.
