DIRAC Setup Structure
The basic DIRAC components are Services, APIs, Agents, and Executors.
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.
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.
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 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 providing a complete functionality to the end user form a DIRAC Setup. All DIRAC client installations will point to a particular DIRAC Setup. Setups can span multiple server installations. Each server installation belongs to a DIRAC Instance that can be shared by multiple Setups.
A Setup is the highest level of the DIRAC component hierarchy. Setups are combining together instances of Systems. Within a given installation there may be several Setups. For example, there can be “Production” Setup together with “Test” or “Certification” Setups used for development and testing of the new functionality. An instance of a System can belong to one or more Setups, in other words, different Setups can share some System instances. Multiple Setups for the given community share the same Configuration information which allows them to access the same computing resources.
Each System and Setup instance has a distinct name. The mapping of Systems to Setups is described in the Configuration of the DIRAC installation in the “/DIRAC/Setups” section.