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Templates: Post-Processors

The post-processor section within a template configures any post-processing that will be done to images built by the builders. Examples of post-processing would be compressing files, uploading artifacts, etc.

Post-processors are optional. If no post-processors are defined within a template, then no post-processing will be done to the image. The resulting artifact of a build is just the image outputted by the builder.

This documentation page will cover how to configure a post-processor in a template. The specific configuration options available for each post-processor, however, must be referenced from the documentation for that specific post-processor.

Within a template, a section of post-processor definitions looks like this:

{
  "post-processors": [
    ... one or more post-processor definitions here ...
  ]
}

For each post-processor definition, Packer will take the result of each of the defined builders and send it through the post-processors. This means that if you have one post-processor defined and two builders defined in a template, the post-processor will run twice (once for each builder), by default. There are ways, which will be covered later, to control what builders post-processors apply to, if you wish.

Post-Processor Definition

Within the post-processors array in a template, there are three ways to define a post-processor. There are simple definitions, detailed definitions, and sequence definitions. Don't worry, they're all very easy to understand, and the "simple" and "detailed" definitions are simply shortcuts for the "sequence" definition.

A simple definition is just a string; the name of the post-processor. An example is shown below. Simple definitions are used when no additional configuration is needed for the post-processor.

{
  "post-processors": ["compress"]
}

A detailed definition is a JSON object. It is very similar to a builder or provisioner definition. It contains a type field to denote the type of the post-processor, but may also contain additional configuration for the post-processor. A detailed definition is used when additional configuration is needed beyond simply the type for the post-processor. An example is shown below.

{
  "post-processors": [
    {
      "type": "compress",
      "format": "tar.gz"
    }
  ]
}

A sequence definition is a JSON array comprised of other simple or detailed definitions. The post-processors defined in the array are run in order, with the artifact of each feeding into the next, and any intermediary artifacts being discarded. A sequence definition may not contain another sequence definition. Sequnce definitions are used to chain together multiple post-processors. An example is shown below, where the artifact of a build is compressed then uploaded, but the compressed result is not kept.

{
  "post-processors": [
    [
      "compress",
      { "type": "upload", "endpoint": "http://fake.com" }
    ]
  ]
}

As you may be able to imagine, the simple and detailed definitions are simply shortcuts for a sequence definition of only one element.