# Deployment Tasks > New as of 0.5.0 ## Usage ### Overview Sometimes you need to run a command on deployment time, but before an app is completely deployed. Common use cases include: - Checking a database is initialized - Running database migrations - Any commands required to set up the server (e.g. something like a Django `collectstatic`) To support this, Dokku provides support for a special `release` command within your app's `Procfile`, as well as a special `scripts.dokku` key inside of your app's `app.json` file. Be aware that all commands are run within the context of the built docker image - no commands affect the host unless there are volume mounts attached to your app. Each "phase" has different expectations and limitations: - `app.json`: `scripts.dokku.predeploy` - When to use: This should be used if your app does not support arbitrary build commands and you need to make changes to the built image. - Are changes committed to the image at this phase: Yes - Example use-cases - Bundling assets in a slightly different way - Installing a custom package from source or copying a binary into place - `app.json`: `scripts.dokku.postdeploy` - When to use: This should be used in conjunction with external systems to signal the completion of your deploy. - Are changes committed to the image at this phase: No - Example use-cases - Notifying slack that your app is deployed - Coordinating traffic routing with a central load balancer - `app.json`: `scripts.postdeploy` - When to use: This should be used when you wish to run a command _once_, after the app is created and not on subsequent deploys to the app. - Are changes committed to the image at this phase: No - Example use-cases - Setting up OAuth clients and DNS - Loading seed/test data into the app’s test database - `Procfile`: `release` - When to use: This should be used in conjunction with external systems to signal the completion of your app image build. - Are changes committed to the image at this phase: No - Example use-cases - Sending CSS, JS, and other assets from your app’s slug to a CDN or S3 bucket - Priming or invalidating cache stores - Running database migrations Additionally, if using a Dockerfile with an `ENTRYPOINT`, the deployment task is passed to that entrypoint as is. The exceptions are if the entrypoint is one of the following: - `["/tini", "--"]` - `["/bin/tini", "--"]` - `["/usr/bin/tini", "--"]` - `["/usr/local/bin/tini", "--"]` Please keep the above in mind when utilizing deployment tasks. > To execute commands on the host during a release phase, see the [plugin creation documentation](/docs/development/plugin-creation.md) docs for more information on building your own custom plugin. ### Changing the `app.json` location When deploying a monorepo, it may be desirable to specify the specific path of the `app.json` file to use for a given app. This can be done via the `app-json:set` command. If a value is specified and that file does not exist within the repository, Dokku will continue the build process as if the repository has no `app.json` file. ```shell dokku app-json:set node-js-app appjson-path second-app.json ``` The default value may be set by passing an empty value for the option: ```shell dokku app-json:set node-js-app appjson-path ``` The `appjson-path` property can also be set globally. The global default is `app.json`, and the global value is used when no app-specific value is set. ```shell dokku app-json:set --global appjson-path global-app.json ``` The default value may be set by passing an empty value for the option. ```shell dokku app-json:set --global appjson-path ``` ### Displaying app-json reports for an app > New as of 0.25.0 You can get a report about the app's storage status using the `app-json:report` command: ```shell dokku app-json:report ``` ``` =====> node-js-app app-json information App-json computed appjson path: app2.json App-json global appjson path: app.json App-json appjson path: app2.json =====> python-sample app-json information App-json computed appjson path: app.json App-json global appjson path: app.json App-json appjson path: =====> ruby-sample app-json information App-json computed appjson path: app.json App-json global appjson path: app.json App-json appjson path: ``` You can run the command for a specific app also. ```shell dokku app-json:report node-js-app ``` ``` =====> node-js-app app-json information App-json computed appjson path: app2.json App-json global appjson path: app.json App-json appjson path: app2.json ``` You can pass flags which will output only the value of the specific information you want. For example: ```shell dokku app-json:report node-js-app --app-json-appjson-path ``` ``` app2.json ``` ### Deployment tasks #### `app.json` deployment tasks Dokku provides limited support for the `app.json` manifest from Heroku (documentation available [here](https://devcenter.heroku.com/articles/app-json-schema)). The keys available for use with Deployment Tasks are: - `scripts.dokku.predeploy`: This is run _after_ an app's docker image is built, but _before_ any containers are scheduled. Changes made to your image are committed at this phase. - `scripts.dokku.postdeploy`: This is run _after_ an app's containers are scheduled. Changes made to your image are _not_ committed at this phase. - `scripts.postdeploy`: This is run _after_ an app's containers are scheduled. Changes made to your image are _not_ committed at this phase. For buildpack-based deployments, the location of the `app.json` file should be at the root of your repository. Dockerfile-based app deploys should have the `app.json` in the configured `WORKDIR` directory; otherwise Dokku defaults to the buildpack app behavior of looking in `/app`. > Warning: Any failed `app.json` deployment task will fail the deploy. In the case of either phase, a failure will not affect any running containers. The following is an example `app.json` file. Please note that only the `scripts.dokku.predeploy` and `scripts.dokku.postdeploy` tasks are supported by Dokku at this time. All other fields will be ignored and can be omitted. ```json { "scripts": { "dokku": { "predeploy": "touch /app/predeploy.test", "postdeploy": "curl https://some.external.api.service.com/deployment?state=success" }, "postdeploy": "curl https://some.external.api.service.com/created?state=success" } } ``` #### Procfile Release command > New as of 0.14.0 The `Procfile` also supports a special `release` command which acts in a similar way to the [Heroku Release Phase](https://devcenter.heroku.com/articles/release-phase). This command is executed _after_ an app's docker image is built, but _before_ any containers are scheduled. This is also run _after_ any command executed by `scripts.dokku.predeploy`. To use the `release` command, simply add a `release` stanza to your Procfile. ```Procfile release: curl https://some.external.api.service.com/deployment?state=built ``` Unlike the `scripts.dokku.predeploy` command, changes made during by the `release` command are _not_ persisted to disk. > Warning: scaling the release command up will likely result in unspecified issues within your deployment, and is highly discouraged.