| --- |
| title: Execution |
| layout: website-normal |
| --- |
| |
| All processing, whether an effector invocation or a policy cycle, are tracked as ***tasks***. This allows several important capabilities: |
| |
| * active and historic processing can be observed by operators |
| * the invocation context is available in the thread, to check entitlement (permissions) and maintain a |
| hierarchical causal chain even when operations are run in parallel |
| |
| Some executions create new entities, which can then have tasks associated with them, and the system will record, for example, that a start effector on the new entity is a task associated with that entity, with that task |
| created by a task associated with a different entity. |
| |
| The execution of a typical overall start-up sequence is shown below (click image to magnify): |
| |
| [](brooklyn-flow-websequencediagrams.com.png) |
| |
| |
| ## Integration |
| |
| One vital aspect of Brooklyn is its ability to communicate with the systems it starts. This is abstracted using a ***driver*** facility in Brooklyn, where a |
| driver describes how a process or service can be installed and managed using a particular technology. |
| |
| For example, a ``TomcatServer`` may implement start and other effectors using a ``TomcatSshDriver`` which inherits from ``JavaSoftwareProcessSshDriver`` (for JVM and JMX start confguration), inheriting from ``AbstractSoftwareProcessSshDriver`` |
| (for SSH scripting support). |
| |
| Particularly for sensors, some technologies are used so frequently that they are |
| packaged as ***feeds*** which can discover their configuration (including from drivers). These include JMX and HTTP (see ``JmxFeed`` and ``HttpFeed``). |
| |
| Brooklyn comes with entity implementations for a growing number of commonly used systems, including various web application servers, databases and NoSQL data stores, and messaging systems. |
| |
| |
