https://github.com/dontlaugh/packer-plugin-cue

Render files in your Packer builds with CUE
https://github.com/dontlaugh/packer-plugin-cue

cue packer packer-plugin packer-provisioner

Last synced: about 2 months ago
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Render files in your Packer builds with CUE

• Host: GitHub
• URL: https://github.com/dontlaugh/packer-plugin-cue
• Owner: dontlaugh
• License: mpl-2.0
• Created: 2022-10-07T21:14:20.000Z (about 2 years ago)
• Default Branch: main
• Last Pushed: 2024-09-09T02:33:24.000Z (4 months ago)
• Last Synced: 2024-09-09T03:45:00.387Z (4 months ago)
• Topics: cue, packer, packer-plugin, packer-provisioner
• Language: Go
• Homepage:
• Size: 186 KB
• Stars: 5
• Watchers: 2
• Forks: 0
• Open Issues: 0
• Metadata Files:
  • Readme: README.md
  • License: LICENSE

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• awesome-cue - packer-plugin-cue - Render files in your Packer builds with CUE. (Projects)

README

        
# packer-plugin-cue

A packer plugin that writes files to the image you're provisioning, based

on values extracted from a CUE module.

A Packer data provider is TODO.

## Provided Plugins

Provisioners:

* `cue-export` - Given a module, package, and an optional CUE expression, the

  provisioner writes a file with the scalar value or struct yielded by `cue export`.

## Example Usage

Add this plugin to `required_plugins`

```hcl

packer {

  required_plugins {

    cue = {

      version = ">=0.3.1"

      source = "github.com/dontlaugh/cue"

    }

  }

}

```

Write the data yielded by the expression `world` in package `hello` to **/tmp/some-file**

```hcl

  provisioner "cue-export" {

    dir        = "."

    package    = "hello"

    expression = "world"

    dest       = "/tmp/some-file"

  }

```

## Config Attributes

Provisioners:

`cue-export`

* dir - path to where the CUE evaluation should take place

* module - (optional) name of module

* package - (optional) package name, if required to disambiguate

* expression - (optional) CUE expression that yields a specific package value

* dest - path to destination file; Note that some Packer builders

  will not automatically create ancestor directories.

* tags - (optional) list of strings of the form `key=value`

## Explanation

Let's say you have a CUE module with a file **my_service.cue** that looks like this

```cue

package systemd

config_file: "/etc/my-service/config.yaml"

unit_file: '''

[Unit]

Description=My example service

[Service]

Environment=MY_CONFIG=\(config_file)

ExecStart=/usr/bin/my-service

[Install]

WantedBy=multi-user.target

'''

```

Invoking `cue export -p systemd ./my_service.cue` gives you the entire package as JSON

```json

{

    "config_file": "/etc/my-service/config.yaml",

    "unit_file": "W1VuaXRdCkRlc2N...=="

}

```

_Note: We've elided most of the unit file's base64 string here._

Providing `--out binary` and `-e unit_file` lets us select the `unit_file`

field and render it. The value of `config_file` is interpolated.

```

$ cue export -p systemd -e unit_file --out binary ./my_service.cue

[Unit]

Description=My example service

[Service]

Environment=MY_CONFIG=/etc/my-service/config.yaml

ExecStart=/usr/bin/my-service

[Install]

WantedBy=multi-user.target

```

This manner of templating files and interpolating values is useful for machine

image provisioning, and this plugin provides a declarative API for rendering CUE

to files during a Packer build.

The previous examples use the `cue` CLI, which you should definitely download

and experiment with if you are unfamiliar with CUE. This plugin, however, uses

CUE as a Go library.

### But wait, there's more!

The `cue-export` provisioner doesn't need a string or binary template to write

files. If the package (with optional expression) evaluates  to a string, number,

or struct type, this plugin does the following

* String and number types are written as a single-line file to `dest`

* Struct types must be given a `serialize` config, one of "json", "yaml",

  or "toml". The entire struct will be serialized in tha format.

A quick example of a struct rendered to yaml

```hcl

provisioner "cue-export" {

    module     = "."

    dir        = "."

    package    = "prometheus"

    expression = "config_yaml"

    serialize  = "yaml"

    dest       = "/tmp/prometheus.yaml"

}

```

If your expression evaluates to a struct and no serializer is set, it's an error.