Introduced in 0.26.0
Schedulers are a way of customizing how an app image is deployed, and can be used to interact with non-local systems such as Kubernetes and Nomad.
Dokku supports the following built-in schedulers:
scheduler-docker-local: Schedules apps against the local docker socket and runs containers directly on the Dokku host. See the docker-local scheduler documentation for more information on how this scheduler functions.
scheduler-null: Does nothing during the scheduler phase. See the null scheduler documentation for more information on how this scheduler functions.
Overriding the auto-selected scheduler¶
If desired, the scheduler can be specified via the
scheduler:set command by speifying a value for
selected. The selected scheduler will always be used.
The default value may be set by passing an empty value for the option:
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.
The default value may be set by passing an empty value for the option.
Displaying scheduler reports for an app¶
You can get a report about the app's scheduler status using the
=====> node-js-app scheduler information Scheduler computed selected: herokuish Scheduler global selected: herokuish Scheduler selected: herokuish =====> python-sample scheduler information Scheduler computed selected: dockerfile Scheduler global selected: herokuish Scheduler selected: dockerfile =====> ruby-sample scheduler information Scheduler computed selected: herokuish Scheduler global selected: herokuish Scheduler selected:
You can run the command for a specific app also.
You can pass flags which will output only the value of the specific information you want. For example:
Implementing a Scheduler¶
Custom plugins names must have the prefix
scheduler- or scheduler overriding via
scheduler:set may not function as expected.
At this time, the following dokku commands are used to implement a complete scheduler.
apps:destroy: stops the app processes on the scheduler
- triggers: post-delete, scheduler-register-retired, scheduler-retire
apps:rename: handles app renaming
- triggers: post-app-rename-setup
apps:clone: handles app cloning
- triggers: post-app-clone-setup
deploy: deploys app proceses and checks the status of a deploy
- triggers: scheduler-app-status, scheduler-deploy, scheduler-is-deployed, scheduler-logs-failed
enter: enters a running container
- triggers: scheduler-enter
logs: fetches app logs
- triggers: scheduler-logs
run: starts one-off run containers (detached and non-detached) as well as listing run processes
- triggers: scheduler-run, scheduler-run-list
ps:stop: stops app processes
- triggers: scheduler-stop
ps:inspect: outputs inspect output for processes in an app
- triggers: scheduler-inspect
Schedulers may decide to omit some functionality here, or use plugin triggers to supplement config with information from other plugins. Additionally, a scheduler may implement other triggers in order handle any extra processes needed during a deploy.
Schedulers can use any tools available on the system to build the docker image, and may even be used to interact with off-server systems. The only current requirement is that the scheduler must have access to the image built in the build phase. If this is not the case, the registry plugin can be used to push the image to a registry that the scheduler software can access.
Deployment tasks are currently executed directly on the primary Dokku server.