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Process and Container 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>]                       # 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

Warning: This section applies only to git-based deploys, and only works deterministically for these apps. Please see the images documentation and tar documentation in for more information concerning rebuilding those 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

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

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

Scaling apps

Via CLI

This functionality is disabled if the formation is managed via a file such as DOKKU_SCALE.

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 DOKKU_SCALE formation file disables the ability to use ps:scale for scaling.

A DOKKU_SCALE file can be committed to the root of the pushed app repository, and must be within the built image artifact in the image's working directory as shown below.

  • Buildpacks: /app/DOKKU_SCALE
  • Dockerfile: WORKDIR/DOKKU_SCALE or /DOKKU_SCALE
  • Docker Image: WORKDIR/DOKKU_SCALE or /DOKKU_SCALE

The DOKKU_SCALE file format is as follows:

web=1
worker=2

Removing the file will result in Dokku respecting the ps:scale command for setting scale values.

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 others - may be managed via ps:scale or a DOKKU_SCALE formation file either before or after the initial deploy.

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

  • Custom checks defined by a CHECKS file only apply to the web process type.
  • By default, the built-in nginx proxy implementation only proxies the web process (others may be handled via a custom nginx.conf.sigil).
  • Only the web process may be bound to an external port.

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.

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 restart policy:             on-failure:10
       Restore:                       true
       Running:                       false
=====> python-sample ps information
       Deployed:                      false
       Processes:                     0
       Ps can scale:                  true
       Ps restart policy:             on-failure:10
       Restore:                       true
       Running:                       false
=====> ruby-sample ps information
       Deployed:                      false
       Processes:                     0
       Ps can scale:                  true
       Ps restart policy:             on-failure:10
       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
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