The build block

Note: This page is about HCL2 Packer templates. HCL2 templates were first introduced as a beta feature into Packer version 1.5. As of v1.7, HCL2 support is no longer in beta, and is the preferred way to write Packer configuration. For the old-style stable configuration language see template docs. As of v1.6.2, you can convert your legacy JSON template into an HCL2 config file using the hcl2_upgrade command.

The build block defines what builders are started, how to provision them and if necessary what to do with their artifacts using post-process.

To use builders in a build block you can either:

Set the sources array of string with references to pre-defined sources.
Define build-level source blocks. This also allows you to set specific fields.

# build.pkr.hcl
build {
    # use the `name` field to name a build in the logs.
    # For example this present config will display
    # "buildname.amazon-ebs.example-1" and "buildname.amazon-ebs.example-2"
    name = "buildname"

    sources = [
        # use the optional plural `sources` list to simply use a `source`
        # without changing any field.
        "source.amazon-ebs.example-1",
    ]

    source "source.amazon-ebs.example-2" {
        # Use the singular `source` block set specific fields.
        # Note that fields cannot be overwritten, in other words, you cannot
        # set the 'output' field from the top-level source block and here.
        output = "different value"
        name = "differentname"
    }

    provisioner "shell" {
        scripts = fileset(".", "scripts/{install,secure}.sh")
    }

    post-processor "shell-local" {
        inline = ["echo Hello World from ${source.type}.${source.name}"]
    }
}

Define top-level source blocks to configure your builders. The list of available builders can be found in the builders section.

Naming your builds

The optional name field of the build block can be used to set the name of a build. Named builds will prefix the log lines in a packer build with the name of the build block. For example:

source "null" "first-example" {
    communicator = "none"
}

source "null" "second-example" {
    communicator = "none"
}

build {
    name = "a"

    sources = [
        "sources.null.first-example",
        "sources.null.second-example",
    ]
}


build {
    sources = ["sources.null.second-example"]
}

Will output:

> packer build ./folder
Build 'a.null.first-example' finished.
Build 'a.null.second-example' finished.
Build 'null.second-example' finished.

==> Builds finished. The artifacts of successful builds are:
--> a.null.first-example: Did not export anything. This is the null builder
--> a.null.second-example: Did not export anything. This is the null builder
--> null.second-example: Did not export anything. This is the null builder

Running only specific builds

The -only/-except flags will match a source's type.name and run 'only' matching builders (source) or all referenced builders 'except' the matching ones, for example with the same config file:

> packer build -only "*.second-example" ./folder
Build 'null.second-example' finished.
Build 'a.null.second-example' finished.

==> Builds finished. The artifacts of successful builds are:
--> a.null.second-example: Did not export anything. This is the null builder
--> null.second-example: Did not export anything. This is the null builder

Here 'a.null.first-example' was skipped.

Note: It is not yet possible to match a named build block to do this, but this is soon going to be possible. So here "a.*" will match nothing.

A list of community builders is available.
Create your own custom builder !

The build block

Naming your builds

Running only specific builds

Related