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• EDSL Concepts
• Ketrew's Engine

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Glossary

Here are some common terms used in this documentation.

EDSL Concepts

A node (function Ketrew.EDSL.workflow_node) is the basic building block of a workflow (it is often also called a “target”). A workflow-node has many components:

• A build-process describes how a program should be run, usually on a given host; for example the function Ketrew.EDSL.pbs returns a datastructure representing the action of running a program on a host with the PBS batch scheduler. It is the parameter ?make of Ketrew.EDSL.workflow_node.
  • A host (Ketrew.EDSL.Host.t) is a place where one can run things. Usually a host is an SSH host with a “playground”, and a few other options.
  • A playground is a directory on a host where the Ketrew engine and its plugins can (and will) write log files, temporary scripts, etc. Most features which use hosts require playgrounds and will fail if not provided.
  • A program (Ketrew.EDSL.Program.t) is a datastructure representing shell scripts on steroids, Ketrew provides high-level combinators to build programs.
• A condition (Ketrew.EDSL.Condition.t) defines how to tell if a node should be run or not (it is set by the “product” of the node or by the argument ?done_when of Ketrew.EDSL.workflow_node).
• Links to other nodes, i.e., edges:
  • Ketrew.EDSL.depends_on are nodes that need to be satisfied or run before a node can start running,
  • Ketrew.EDSL.on_failure_activate are nodes that will be activated if the node fails (being killed is considered failing here), and
  • Ketrew.EDSL.on_success_activate are nodes that will be activated only after a node succeeds.
• Metadata and tags are user-provided information; the ?metadata is, for now, just a raw string; the ?tags are a list of strings which are “searchable” (see “filters” in the UI).
• An Equivalence specification tells the engine when to consider a node redundant, the default value is the most common and obvious, `Same_active_condition:
  
  • when adding a node to the engine, if an active or activable node already has the same condition then the new one is considered redundant and will be replaced with a pointer to the older one;
  • the behavior above can be cancelled by providing `None (cf. Ketrew_pure.Target.Equivalence.t).

In the EDSL, a workflow-node has a product which defines, via its #is_done method, how the condition of the node is tested. The product of a node can be accessed through the #product method.

Ketrew's Engine

Ketrew's engine is the process in charge of orchestrating and monitoring the run of the workflows.

• In standalone mode, the command line application has to run the engine manually.
• In client-server mode, the engine is run by the server; the client applications just “submit” workflows.

The engine runs long-running processes through plugins (see documentation).