dokku/docs/processes/process-management.md

Process Management

New as of 0.3.14, Enhanced in 0.7.0

ps:inspect <app>                                                  # Displays a sanitized version of docker inspect for an app
ps:rebuild [--parallel count] [--all|<app>]                       # Rebuilds an app from source
ps:report [<app>] [<flag>]                                        # Displays a process report for one or more apps
ps:restart [--parallel count] [--all|<app>]  [<process-name>]     # Restart an app
ps:restore [<app>]                                                # Start previously running apps e.g. after reboot
ps:scale [--skip-deploy] <app> <proc>=<count> [<proc>=<count>...] # Get/Set how many instances of a given process to run
ps:set <app> <key> <value>                                        # Set or clear a ps property for an app
ps:start [--parallel count] [--all|<app>]                         # Start an app
ps:stop [--parallel count] [--all|<app>]                          # Stop an app

Usage

Inspecting app containers

New as of 0.13.0

A common administrative task to perform is calling docker inspect on the containers that are running for an app. This can be an error-prone task to perform, and may also reveal sensitive environment variables if not done correctly. Dokku provides a wrapper around this command via the ps:inspect command:

dokku ps:inspect node-js-app

This command will gather all the running container IDs for your app and call docker inspect, sanitizing the output data so it can be copy-pasted elsewhere safely.

Rebuilding apps

It may be useful to rebuild an app at will, such as for commands that do not rebuild an app or when skipping a rebuild after setting multiple config values. For these use cases, the ps:rebuild function can be used.

dokku ps:rebuild node-js-app

All apps may be rebuilt by using the --all flag.

dokku ps:rebuild --all

By default, rebuilding all apps happens serially. The parallelism may be controlled by the --parallel flag.

dokku ps:rebuild --all --parallel 2

Finally, the number of parallel workers may be automatically set to the number of CPUs available by setting the --parallel flag to -1

dokku ps:rebuild --all --parallel -1

A missing linked container will result in failure to boot apps. Services should all be started for apps being rebuilt.

Restarting apps

An app may be restarted using the ps:restart command.

dokku ps:restart node-js-app

A single process type - such as web or worker - may also be specified. This does not support specifying a given instance of a process type, and only supports restarting all instances of that process type.

dokku ps:restart node-js-app web

All apps may be restarted by using the --all flag. This flag is incompatible with specifying a process type.

dokku ps:restart --all

By default, restarting all apps happens serially. The parallelism may be controlled by the --parallel flag.

dokku ps:restart --all --parallel 2

Finally, the number of parallel workers may be automatically set to the number of CPUs available by setting the --parallel flag to -1

dokku ps:restart --all --parallel -1

A missing linked container will result in failure to boot apps. Services should all be started for apps being rebuilt.

Displaying existing scale properties

Issuing the ps:scale command with no arguments will output the current scaling properties for an app.

dokku ps:scale node-js-app

-----> Scaling for python
proctype: qty
--------: ---
web:  1

Defining Processes

Procfile

Note: Dokku supports the Procfile format as defined in this document under "Strict Mode" parsing rules.

Apps can define processes to run by using a Procfile. A Procfile is a simple text file that can be used to specify multiple commands, each of which is subject to process scaling. In the case where the built image sets a default command to run - either through usage of CMD for Dockerfile-based builds, a default process for buildpack-based builds, or any other method for the builder in use - the Procfile will take precedence.

If the file exists, it should not be empty, as doing so may result in a failed deploy.

The syntax for declaring a Procfile is as follows. Note that the format is one process type per line, with no duplicate process types.

<process type>: <command>

If, for example, you have multiple queue workers and wish to scale them separately, the following would be a valid way to work around the requirement of not duplicating process types:

worker:           env QUEUE=* bundle exec rake resque:work
importantworker:  env QUEUE=important bundle exec rake resque:work

If the app build declares an ENTRYPOINT, the command defined in the Procfile is passed as an argument to that entrypoint. This is the case for all Dockerfile-based, Docker Image, and Cloud Native Buildpack deployments.

The web process type holds some significance in that it is the only process type that is automatically scaled to 1 on the initial application deploy. See the web process scaling documentation for more details around scaling individual processes.

See the Procfile location documentation for more information on where to place your Procfile file.

The web process

For initial app deploys, Dokku will default to starting a single web process for each app. This process may be defined within the Procfile or as the CMD (for Dockerfile or Docker image deploys). Scaling of the web process - and all other processes - may be managed via ps:scale or the formation key in the app.json file either before or after the initial deploy.

There are also a few other exceptions for the web process.

• By default, the built-in nginx proxy implementation only proxies the web process (others may be handled via a custom nginx.conf.sigil).
  • See the nginx request proxying documentation for more information on how nginx handles proxied requests.
• Only the web process may be bound to an external port.

The release process

The Procfile also supports a special release command which acts in a similar way to the Heroku Release Phase. See the Release deployment task documentation for more information on how Dokku handles this process type.

Changing the Procfile location

When deploying a monorepo, it may be desirable to specify the specific path of the Procfile file to use for a given app. This can be done via the ps: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 Procfile.

For deploys via the git:from-image and git:load-image commands, the Procfile is extracted from the configured WORKDIR property of the image. For all other deploys - git push, git:from-archive, git:sync - will have the Procfile extracted directly from the source code. Both cases will respect the configured procfile-path property value.

dokku ps:set node-js-app procfile-path .dokku/Procfile

The default value may be set by passing an empty value for the option:

dokku ps:set node-js-app procfile-path

The procfile-path property can also be set globally. The global default is Procfile, and the global value is used when no app-specific value is set.

dokku ps:set --global procfile-path global-Procfile

The default value may be set by passing an empty value for the option.

dokku ps:set --global procfile-path

Scaling apps

Via CLI

This functionality is disabled if the formation is managed via the formation key of app.json.

Dokku can also manage scaling itself via the ps:scale command. This command can be used to scale multiple process types at the same time.

dokku ps:scale node-js-app web=1

Multiple process types can be scaled at once:

dokku ps:scale node-js-app web=1 worker=1

If desired, the corresponding deploy will be skipped by using the --skip-deploy flag:

dokku ps:scale --skip-deploy node-js-app web=1

Manually managing process scaling

Using a formation key in an app.json file with any quantity specified disables the ability to use ps:scale for scaling. All processes not specified in the app.json will have their process count set to zero.

Users can also configure scaling within the codebase itself to manage process scaling. The formation key should be specified as follows in the app.json file:

{
  "formation": {
    "web": {
      "quantity": 1
    },
    "worker": {
      "quantity": 4
    }
  }
}

Removing the formation key or removing the app.json file from your repository will result in Dokku respecting the ps:scale command for setting scale values. The values set via the app.json file from a previous deploy will be respected.

See the app.json location documentation for more information on where to place your app.json file.

Stopping apps

Deployed apps can be stopped using the ps:stop command. This turns off all running containers for an app, and will result in a 502 Bad Gateway response for the default nginx proxy implementation.

dokku ps:stop node-js-app

All apps may be stopped by using the --all flag.

dokku ps:stop --all

By default, stopping all apps happens serially. The parallelism may be controlled by the --parallel flag.

dokku ps:stop --all --parallel 2

Finally, the number of parallel workers may be automatically set to the number of CPUs available by setting the --parallel flag to -1

dokku ps:stop --all --parallel -1

Starting apps

All stopped containers can be started using the ps:start command. This is similar to running ps:restart, except no action will be taken if the app containers are running.

dokku ps:start node-js-app

All apps may be started by using the --all flag.

dokku ps:start --all

By default, starting all apps happens serially. The parallelism may be controlled by the --parallel flag.

dokku ps:start --all --parallel 2

Finally, the number of parallel workers may be automatically set to the number of CPUs available by setting the --parallel flag to -1

dokku ps:start --all --parallel -1

Restart policies

New as of 0.7.0, Command Changed in 0.22.0

By default, Dokku will automatically restart containers that exit with a non-zero status up to 10 times via the on-failure Docker restart policy.

Setting the restart policy

A change in the restart policy must be followed by a ps:rebuild call.

You can configure this via the ps:set command:

# always restart an exited container
dokku ps:set node-js-app restart-policy always

# never restart an exited container
dokku ps:set node-js-app restart-policy no

# only restart it on Docker restart if it was not manually stopped
dokku ps:set node-js-app restart-policy unless-stopped

# restart only on non-zero exit status
dokku ps:set node-js-app restart-policy on-failure

# restart only on non-zero exit status up to 20 times
dokku ps:set node-js-app restart-policy on-failure:20

Restart policies have no bearing on server reboot, and Dokku will always attempt to restart your apps at that point unless they were manually stopped.

Dokku also runs dokku-event-listener in the background via the system's init service. This monitors container state, performing the following actions:

• If a web process restarts and it's container IP address changes, the app's proxy configuration will be rebuilt.
• If a process within an app exceeds the restart count, the app will be rebuilt.

Displaying reports for an app

New as of 0.12.0

You can get a report about the deployed apps using the ps:report command:

dokku ps:report

=====> node-js-app ps information
       Deployed:                      false
       Processes:                     0
       Ps can scale:                  true
       Ps computed procfile path:     Procfile2
       Ps global procfile path:       Procfile
       Ps restart policy:             on-failure:10
       Ps procfile path:              Procfile2
       Restore:                       true
       Running:                       false
=====> python-sample ps information
       Deployed:                      false
       Processes:                     0
       Ps can scale:                  true
       Ps computed procfile path:     Procfile
       Ps global procfile path:       Procfile
       Ps restart policy:             on-failure:10
       Ps procfile path:
       Restore:                       true
       Running:                       false
=====> ruby-sample ps information
       Deployed:                      false
       Processes:                     0
       Ps can scale:                  true
       Ps computed procfile path:     Procfile
       Ps global procfile path:       Procfile
       Ps restart policy:             on-failure:10
       Ps procfile path:
       Restore:                       true
       Running:                       false

You can run the command for a specific app also.

dokku ps:report node-js-app

=====> node-js-app ps information
       Deployed:                      false
       Processes:                     0
       Ps can scale:                  true
       Ps restart policy:             on-failure:10
       Restore:                       true
       Running:                       false

You can pass flags which will output only the value of the specific information you want. For example:

dokku ps:report node-js-app --deployed

Restoring apps after a server reboot

When a server reboots or Docker is restarted/upgraded, Docker may or may not start old app containers automatically, and may in some cases re-assign container IP addresses. To combat this issue, Dokku uses an init process that triggers dokku ps:restore after the Docker daemon is detected as starting. When triggered, the dokku ps:restore command will serially (one by one) run the following for each:

• Start all linked services.
• Clear generated proxy configuration files.
• Start the app if it has not been manually stopped.
  • If the app containers still exist, they will be started and the generated proxy configuration files will be rebuilt.
  • If any of the app containers are missing, the entire app will be rebuilt.

During this time, requests may route to the incorrect app if the assigned IPs correspond to those for other apps. While dokku makes all efforts to avoid this, there may be a few minutes where urls may route to the wrong app. To avoid this, either use a custom proxy plugin or wait a few minutes until the restoration process is complete.