feat: add a Railpack builder to Dokku

Closes #7615

docs/appendices/file-formats/railpack-json.md

@@ -0,0 +1,3 @@
+# railpack.json
+
+The `railpack.json` file is used to configure an application when built with the `railpack` builder. Please refer to the [railpack.json documentation](https://railpack.com/config/file) for more information.

docs/deployment/builders/railpack.md

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+# Railpack
+
+> [!IMPORTANT]
+> New as of 0.32.0
+
+The `railpack` builder builds apps via [Railpack](https://railpack.com/), a buildpack alternative.
+
+## Usage
+
+### Requirements
+
+The `railpack` cli tool is not included by default with Dokku or as a dependency. It must also be installed as shown on [this page](https://railpack.com/installation).
+
+Builds will proceed with the `railpack` cli for the app from then on.
+
+### Detection
+
+This builder will be auto-detected in the following case:
+
+- A `railpack.json` exists in the root of the app repository.
+
+The builder may also be selected via the `builder:set` command
+
+```shell
+dokku builder:set node-js-app selected railpack
+```
+
+### Supported languages
+
+See the [upstream railpack documentation](https://railpack.com/) for further information on what languages and frameworks are supported.
+
+### Build-time configuration variables
+
+For security reasons - and as per [Docker recommendations](https://github.com/docker/docker/issues/13490) - railpack-based deploys have variables available only during runtime.
+
+For users that require customization in the `build` phase, you may use build arguments via the [docker-options plugin](/docs/advanced-usage/docker-options.md). All environment variables set by the `config` plugin are automatically exported within the railpack build environment, and thus `--env` only requires setting a key without a value.
+
+```shell
+dokku docker-options:add node-js-app build '--env NODE_ENV'
+```
+
+Alternatively, a full value may be provided in the form of `--env KEY=VALUE`:
+
+```shell
+dokku docker-options:add node-js-app build '--env NODE_ENV=production'
+```
+
+### Changing the `railpack.json` location
+
+The `railpack.json` is expected to be found in a specific directory, depending on the deploy approach:
+
+- The `WORKDIR` of the Docker image for deploys resulting from `git:from-image` and `git:load-image` commands.
+- The root of the source code tree for all other deploys (git push, `git:from-archive`, `git:sync`).
+
+Sometimes it may be desirable to set a different path for a given app, e.g. when deploying from a monorepo. This can be done via the `railpackjson-path` property:
+
+```shell
+dokku builder-railpack:set node-js-app railpackjson-path .dokku/railpack.json
+```
+
+The value is the path to the desired file *relative* to the base search directory, and will never be treated as absolute paths in any context. If that file does not exist within the repository, the build will fail.
+
+The default value may be set by passing an empty value for the option:
+
+```shell
+dokku builder-railpack:set node-js-app railpackjson-path
+```
+
+The `railpackjson-path` property can also be set globally. The global default is `railpack.json`, and the global value is used when no app-specific value is set.
+
+```shell
+dokku builder-railpack:set --global railpackjson-path railpack2.json
+```
+
+The default value may be set by passing an empty value for the option.
+
+```shell
+dokku builder-railpack:set --global railpackjson-path
+```
+
+### Disabling cache
+
+Cache is enabled by default, but can be disabled by setting the `no-cache` property to `true`:
+
+```shell
+dokku builder-railpack:set node-js-app no-cache true
+```
+
+The default value may be set by passing an empty value for the option:
+
+```shell
+dokku builder-railpack:set node-js-app no-cache
+```
+
+The `no-cache` property can also be set globally. The global default is `false`, and the global value is used when no app-specific value is set.
+
+```shell
+dokku builder-railpack:set --global no-cache true
+```
+
+The default value may be set by passing an empty value for the option.
+
+```shell
+dokku builder-railpack:set --global no-cache
+```
+
+### Displaying builder-railpack reports for an app
+
+You can get a report about the app's storage status using the `builder-railpack:report` command:
+
+```shell
+dokku builder-railpack:report
+```
+
+```
+=====> node-js-app builder-railpack information
+       Builder-railpack computed railpackjson path: railpack2.json
+       Builder-railpack global railpackjson path:   railpack.json
+       Builder-railpack railpackjson path:          railpack2.json
+       Builder-railpack computed no cache:          true
+       Builder-railpack global no cache:            false
+       Builder-railpack no cache:                   true
+=====> python-sample builder-railpack information
+       Builder-railpack computed railpackjson path: railpack.json
+       Builder-railpack global railpackjson path:   railpack.json
+       Builder-railpack railpackjson path:
+       Builder-railpack computed no cache:          false
+       Builder-railpack global no cache:            false
+       Builder-railpack no cache:
+=====> ruby-sample builder-railpack information
+       Builder-railpack computed railpackjson path: railpack.json
+       Builder-railpack global railpackjson path:   railpack.json
+       Builder-railpack railpackjson path:
+       Builder-railpack computed no cache:          false
+       Builder-railpack global no cache:            false
+       Builder-railpack no cache:
+```
+
+You can run the command for a specific app also.
+
+```shell
+dokku builder-railpack:report node-js-app
+```
+
+```
+=====> node-js-app builder-railpack information
+       Builder-railpack computed railpackjson path: railpack2.json
+       Builder-railpack global railpackjson path:   railpack.json
+       Builder-railpack railpackjson path:          railpack2.json
+       Builder-railpack computed no cache:          true
+       Builder-railpack global no cache:            false
+       Builder-railpack no cache:                   true
+```
+
+You can pass flags which will output only the value of the specific information you want. For example:
+
+```shell
+dokku builder-railpack:report node-js-app --builder-railpack-no-cache
+```
+
+```
+true
+```

docs/template.html

@@ -150,6 +150,7 @@
             <a href="/{{NAME}}/deployment/builders/lambda/" class="list-group-item">Lambda Builder</a>
             <a href="/{{NAME}}/deployment/builders/nixpacks/" class="list-group-item">Nixpacks Builder</a>
             <a href="/{{NAME}}/deployment/builders/null/" class="list-group-item">Null Builder</a>
+            <a href="/{{NAME}}/deployment/builders/railpack/" class="list-group-item">Railpack Builder</a>
 
             <a href="#" class="list-group-item disabled">Deployment Methods</a>
             <a href="/{{NAME}}/deployment/methods/git/" class="list-group-item">Git Deployment</a>