Cylc Documentation

First read the front page of this website, then:

Note that SUITE is just another word for WORKFLOW in Cylc docs (this is numerical weather prediction terminology that dates back a long way).

The Cylc User Guide


Please cite Cylc in your publications if you use it to automate your workflows.

Response to “Assessment Report on Autosubmit, Cylc and ecFlow”

The Cylc developers would like to respond to a recent comparison paper, Assessment report on Autosubmit, Cylc and ecFlow (2016, Domingo Manubens-Gil et. al.) and another that references it, Seamless Management of Ensemble Climate Prediction Experiments on HPC Platforms (2016, Domingo Manubens-Gil et. al.). Two of us are listed as contributors to the first paper but it should be noted that the contribution was limited by time and workload constraints to major corrections relating to Cylc (all of which were addressed by the lead author).

The lead author of both papers is also the lead developer of Autosubmit. Perhaps inevitably as the developers of Cylc we have a rather different view on the strengths and weaknesses of the different systems. In particular we would like to address the following points.


A Cycling Workflow Example

The following example is intended to convey something of basic Cylc functionality. However, it barely scratches the surface; to understand more, read the User Guide!

Create A New workflow

# suite.rc:
  initial cycle point = 2021
  final cycle point = 2023
    [[[R1]]]  # Initial cycle point.
      graph = prep => model
    [[[R//P1Y]]]  # Yearly cycling.
      graph = model[-P1Y] => model => post
    [[[R1/P0Y]]]  # Final cycle point.
      graph = post => stop

  [[root]]  # Inherited by all tasks.
    script = sleep 10
    script = echo "my FOOD is $FOOD"; sleep 10
      FOOD = icecream
    # ...
  # ...

Register, Validate, and Visualize

$ cylc register test1 ~/suites/test/suite.rc
REGISTER test1: /home/bob/suites/test

$ cylc print test1
test1 | A first test suite | ~/suites/test

$ cylc edit test1  # Open the workflow in your editor again.

$ cylc help  # See other commands!

$ cylc validate test1
Valid for cylc-7.8.1

$ cylc graph test1 &


$ cylc register test1 ~/suites/test/suite.rc
REGISTER test1: /home/bob/suites/test

$ cylc print test1
test1 | A first test suite | ~/suites/test

$ cylc edit test1  # Open the workflow in your editor again.

$ cylc help  # See other commands!

$ cylc validate test1
Valid for cylc-7.8.1

$ cylc graph test1 &

View Task Job Output

$ cylc log -m cat -f o test1 model.2021

Suite    : test1
Task Job : 2021/model/01 (try 1)

my FOOD is icecream

2017-03-20T19:37:49Z NORMAL - started
2017-03-20T19:37:59Z NORMAL - succeeded

Frequently Asked Questions

(This FAQ is still new and will be added to in time).

What are the major capabilities and features of Cylc?

See the front page of this website

Does Cylc automatically manage task data?

No. For maximum flexibility and generality, Cylc is a pure orchestration engine that manages task execution according to abstract dependencies. It is left to the workflow designer to make sure that the tasks use shared data areas or move data around as needed, by whatever means is appropriate to your data types and platforms. (Cylc does provide easy access to a self-contained shared data area for each workflow). This is easy to do, and it avoids the risk of restrictive assumptions or unnecessary data movement.

We do note however that there are good use cases for a “data modeling” approach whereby the workflow structure self-assembles from explicit data dependencies, and the workflow engine may automatically manage the data too. Cylc actually uses a self-assembling workflow model internally, and we are considering exposing this again as an option in the future.

Does Cylc have built-in Cloud and Container “integration”?

No, because our historical home base is production weather forecasting, and related systems, which is still almost entirely done on in-house HPC systems. Cloud and containers are definitely coming soon to this world too, but for the moment you’ll have to “roll your own” use of Cylc with them. That is easy enough to do though because Cylc runs on any Linux VM and the jobs that it manages can do anything you want.

Does Cylc support the Common Workflow Language?

No, Cylc doesn’t support CWL at this stage because CWL does not understand cycling workflows (see for example the eWaterCycle Case Study in the Cylc CiSE paper).


Cylc 8 web UI (coming soon...)

Cylc 8 is currently in development. It is Python 3 based with a new web UI and supporting architecture.

Cylc 7 GUI graph and dot views

The gcylc suite control GUI can display two of three views at once. Colors represent different task states. The graph view shows the suite dependency structure. The dot view shows task spread over cycle points.

Cylc 7 GUI tree view

The gcylc text tree view shows the most information about tasks in a running suite.

Cylc 7 gscan GUI

The gscan GUI shows a minimal state summary view of all your running suites. Click on a suite to open a gcylc suite control GUI for it.

static visualization 1

This shows a moderately large operational cycling workflow.

static visualization 2

Another suite with families partially collapsed (inset) and fully expanded. Automatic coloring of parameterized tasks with a Jinaj2 loop over Hue in the HSV color space.

static visualization 3

A big one! (4.8M SVG format - you may need to use your horizontal and vertical browser scroll bars to find the image).