+Summary Of Major Changes
+
+Terminology
+Cylc now uses more widely understood terms for several core concepts.
+
+
+Cylc 7 Term |
+Cylc 8 Term |
+
|---|
+
+
+suite |
+workflow |
+
+batch system |
+job runner |
+
+suite daemon |
+scheduler |
+
+suite.rc
|
+flow.cylc
|
+
+
+
+Note the configuration filename is now flow.cylc, not suite.rc.
+
+
+Cylc 7 Compatibility Mode
+Continuing to use the old suite.rc filename triggers a backward
+compatibility mode in Cylc 8 which supports Cylc 7
+workflow configurations out of the box, with
+some caveats. However, to future-proof
+your workflow and take full advantage of Cylc 8 you should upgrade to Cylc 8 syntax.
+
+
+Upgrading To Cylc 8
+
+There have been some configuration changes at Cylc 8.
+To upgrade your Cylc 7 suite to a Cylc 8 workflow, first make sure it validates
+in Cylc 7 without any warnings, then rename the workflow configuration file
+from suite.rc to flow.cylc, then run cylc validate in Cylc 8 and
+take action on any warnings.
+
+
Note
+
Validation warnings use a shorthand notation
+to refer to nested configuration settings on a single line, like this:
+[section][sub-section]item.
+
New Web and Terminal UIs
+
+At Cylc 8, there are two UIs available to monitor and control your workflows:
+
+
+
+Command Changes
+cylc run <suite_name> at Cylc 7 has become cylc play <workflow_id>.
+
+At Cylc 8, use cylc pause <workflow_id> to pause a workflow, halting all job
+submission. To restart the workflow, use cylc play <workflow_id>.
+To start a fresh run, use cylc install and play it safely in the new run
+directory.
+(Note that cylc hold and cylc release pause and release individual tasks.)
+
+
+Task/Job States
+Tasks are nodes in the abstract workflow graph, representing
+applications to run at the appropriate point in the workflow. A job
+is the script (and subsequent process) submitted by Cylc to
+actually run the application. A task can have multiple jobs as the result of
+automatic retries or manual re-triggering.
+The 13 task/job states in Cylc 7 have been simplified to 8. Tasks and jobs have been
+separated and states of both can be viewed in the GUI.
+
+For more information, see Task/Job States.
+
+
+Optional and Required Task Outputs
+
+By default, all Cylc 8 tasks are required to succeed - i.e., success is
+a required output. Otherwise they will be marked
+as incomplete tasks needing user intervention.
+In a workflow with incomplete tasks, if there is nothing left to do, the
+scheduler will stall rather than shut down.
+Alternatively, task outputs can be marked as optional.
+This supports graph branching and it allows the scheduler to
+correctly diagnose workflow completion.
+
+
+
+Workflow Installation
+Cylc 8 supports workflow installation.
+For users of Rose, this replaces the functionality of rose suite-run.
+
+Cylc Install
+
+Cylc install cleanly separates workflow source directory from
+run directory. It installs workflow files ready for cylc play.
+$ pwd
+~/cylc-src/demo
+
+$ ls
+flow.cylc
+
+$ cylc install
+INSTALLED demo/run1 from /home/oliverh/cylc-src/demo
+
+$ cylc play demo
+...
+demo/run1: oliver.niwa.local PID=6702
+
+
By default, run numbers increment with each install.
+
+
+File Installation
+When the first job runs on a remote platform (after start-up, or after a cylc reload), a
+remote initialization process is triggered to install workflow files there.
+
+
+Symlink Dirs
+
+Symlinking the workflow directories used by Cylc provides a useful way of
+managing disk space.
+These symlinks are created on a per install target basis, as configured in
+global.cylc[install][symlink dirs]. Install targets are managed on
+a site level, for more information see What Are Install Targets?
+This functionality replaces the Rose root dir configuration
+for Cylc 7 (however, note it does not allow per-workflow configuration).
+
+
+
+Removing Workflows
+Workflows can be deleted with cylc clean - see Removing Workflows. This
+replaces the rose suite-clean functionality.
+
+
+Architecture
+There have been fundamental changes to the architecture of Cylc. You can read
+about the new system design here Architecture.
+
+
+Scheduling Algorithm
+The scheduling algorithm has been changed, more information is available:
+Scheduling Algorithm.
+
+
+Other Changes
+There are an assortment of other features implemented at Cylc 8. Some noteworthy
+minor changes include:
+
+- Runahead Limit
The default runahead limit has been increased from three cycles to five.
+- Queues
Internal Queues are now more efficient (for the scheduler),
+we now recommend using queues to restrict the number of running tasks in
+situations where graphing may have been used previously.
+- Time Zones
[scheduler]cycle point time zone now defaults to UTC, unless you
+are working in Cylc 7 Compatibility Mode.
+- Job Scripts
All user-defined task scripting now runs in a subshell, so you can safely
+switch Python environments inside tasks without affecting Cylc.
+Further information is available in the User Guide: Job Scripts.
+- Packaging
Cylc 8 (and its package dependencies) is now available from Conda Forge and PyPI
+for installations into a Python 3 virtual environment.
+- Remote usernames
If usernames differ on remote job hosts they must now be configured using
+an SSH config file rather than the via Cylc 7 [remote]owner configuration.
+See Remote Usernames.
+
+
+
+
+
+
+
+
+