Cylc can run a workflow without running the real jobs, which may be long-running and resource-hungry.
Dummy mode replaces real jobs with background
sleep jobs on the
scheduler host. This avoids job runner directives that request compute
resources for real workflow tasks, and it allows any workflow configuration to
be run locally in dummy mode.
$ cylc play --mode=dummy <workflow-id> # real dummy jobs
All configured task
script items including
init-script are ignored
in dummy mode. If your
init-script is required to run even local dummy
jobs, the relevant environment setup should be done elsewhere.
Simulation mode does not run real jobs at all, and does not generate job log files.
$ cylc play --mode=simulation <workflow-id> # no real jobs
Simulated Run Length
The default dummy or simulated job run length is 10 seconds. It can be
[runtime][<namespace>][simulation]default run length.
Dummy tasks run locally, so dummy mode does not test communication with remote
job platforms. However, it is easy to write a live-mode test workflow with
sleep 10 tasks that submit to a remote platform.
Alternate path branching is difficult to simulate effectively. You can
configure certain tasks to fail via
[runtime][<namespace>][simulation], but all branches based
on mutually exclusive custom outputs will run because all custom outputs get
artificially completed in dummy mode and in simulation mode.
Run mode is recorded in the workflow run database. Cylc will not let you restart a dummy mode workflow in live mode, or vice versa. Instead, install a new instance of the workflow and run it from scratch in the new mode.