DIRAC Setup Structure

The basic DIRAC components are Services, APIs, Agents, and Executors.

Services

are passive components listening to incoming client requests and reacting accordingly by serving requested information from the Database backend or inserting requests on the Database backend. Services themselves can be clients of other Services from the same DIRAC System or from other Systems.

Agents

are active components, similar to cron jobs, which execution is invoked periodically. Agents are animating the whole system by executing actions, sending requests to the DIRAC or third party services.

Executors

are also active components, similar to consumers of a message queue system, which execution is invoked at request. Executors are used within the DIRAC Workload Management System.

APIs

APIs are implemention of REST interfaces. Their usage is, for the moment, limited to a specific case.

These components are combined together to form Systems. a System is delivering a complex functionality to the rest of DIRAC, providing a solution for a given class of tasks. Examples of Systems are Workload Management System or Configuration System or Data Management System.

And then there are databases, which keep the persistent state of a System. They are accessed by Services and Agents as a kind of shared memory.

To achieve a functional DIRAC installation, cooperation of different Systems is required. A set of Systems provide a complete functionality to the end user. Each System instance has a distinct name.