# Builder Management > [!IMPORTANT] > New as of 0.24.0 ``` builder:report [] [] # Displays a builder report for one or more apps builder:set () # Set or clear a builder property for an app ``` Builders are a way of customizing how an app is built from a source, allowing users flexibility in how artifacts are created for later scheduling. ## Usage ### Builder selection Dokku supports the following built-in builders: - `builder-dockerfile`: Builds apps using a `Dockerfile` via `docker build`. See the [dockerfile builder documentation](/docs/deployment/builders/dockerfiles.md) for more information on how this builder functions. - `builder-herokuish`: Builds apps with Heroku's v2a Buildpack specification via `gliderlabs/herokuish`. See the [herokuish builder documentation](/docs/deployment/builders/herokuish-buildpacks.md) for more information on how this builder functions. - `builder-lambda`: Builds AWS Lambda functions in an environment simulating AWS Lambda runtimes via [lambda-builder](https://github.com/dokku/lambda-builder). See the [lambda builder documentation](/docs/deployment/builders/lambda.md) for more information on how this builder functions. - `builder-null`: Does nothing during the build phase. See the [null builder documentation](/docs/deployment/builders/null.md) for more information on how this builder functions. - `builder-pack`: Builds apps with Cloud Native Buildpacks via the `pack-cli` tool. See the [cloud native buildpacks builder documentation](/docs/deployment/builders/cloud-native-buildpacks.md) for more information on how this builder functions. Builders run a detection script against a source code repository, and the first detected builder will be used to build the app artifact. The exception to this is when a `Dockerfile` is detected and the app is also able to use either `herokuish` or `pack-cli` for building, in which case one of the latter will be chosen. ### Overriding the auto-selected builder If desired, the builder can be specified via the `builder:set` command by specifying a value for `selected`. The selected builder will always be used. ```shell dokku builder:set node-js-app selected dockerfile ``` The default value may be set by passing an empty value for the option: ```shell dokku builder:set node-js-app selected ``` The `selected` property can also be set globally. The global default is an empty string, and auto-detection will be performed when no value is set per-app or globally. ```shell dokku builder:set --global selected herokuish ``` > [!WARNING] > Selecting a global builder will result in _all_ applications using that builder unless a manual override is selected. The default value may be set by passing an empty value for the option. ```shell dokku builder:set --global selected ``` #### Changing the build directory > [!WARNING] > Please keep in mind that setting a custom build directory will result in loss of any changes to the top-level directory, such as the `git.keep-git-dir` property. When deploying a monorepo, it may be desirable to specify the specific build directory to use for a given app. This can be done via the `builder:set` command. If a value is specified and that directory does not exist within the repository, the build will fail. ```shell dokku builder:set node-js-app build-dir app2 ``` The default value may be set by passing an empty value for the option: ```shell dokku builder:set node-js-app build-dir ``` The `build-dir` property can also be set globally. The global default is empty string, and the global value is used when no app-specific value is set. ```shell dokku builder:set --global build-dir app2 ``` The default value may be set by passing an empty value for the option. ```shell dokku builder:set --global build-dir ``` ### Displaying builder reports for an app You can get a report about the app's builder status using the `builder:report` command: ```shell dokku builder:report ``` ``` =====> node-js-app builder information Builder build dir: custom Builder computed build dir: custom Builder computed selected: herokuish Builder global build dir: Builder global selected: herokuish Builder selected: herokuish =====> python-sample builder information Builder build dir: Builder computed build dir: Builder computed selected: dockerfile Builder global build dir: Builder global selected: herokuish Builder selected: dockerfile =====> ruby-sample builder information Builder build dir: Builder computed build dir: Builder computed selected: herokuish Builder global build dir: Builder global selected: herokuish Builder selected: ``` You can run the command for a specific app also. ```shell dokku builder:report node-js-app ``` ``` =====> node-js-app builder information Builder selected: herokuish ``` You can pass flags which will output only the value of the specific information you want. For example: ```shell dokku builder:report node-js-app --builder-selected ``` ### Custom builders To create a custom builder, the following triggers must be implemented: - `builder-build`: - arguments: `BUILDER_TYPE` `APP` `SOURCECODE_WORK_DIR` - description: Creates a docker image named with the output of `common#get_app_image_name $APP`. - `builder-detect`: - arguments: `APP` `SOURCECODE_WORK_DIR` - description: Outputs the name of the builder (without the `builder-` prefix) to use to build the app. - `builder-release`: - arguments: `BUILDER_TYPE` `APP` `IMAGE_AG` - description: A post-build, pre-release trigger that can be used to post-process the image. Usually simply tags and labels the image appropriately. Custom plugins names _must_ have the prefix `builder-` or builder overriding via `builder:set` may not function as expected. Builders can use any tools available on the system to build the docker image, and may even be used to schedule building off-server. The only current requirement is that the image must exist on the server at the end of the `builder-build` command, though this requirement may be relaxed in a future release. For a simple example of how to implement this trigger, see `builder-pack`, which utilizes a cli tool - `pack-cli` - to generate an OCI image that is compatible with Docker and can be scheduled by the official scheduling plugins.