sequencer 1.5.2

The sequencer is used to execute actions in a specified order (for example power on/off clusters)

The sequencer is an engine used by system administrators for the computation and execution of sequences of actions over hardware or software (for example powering on/off a whole cluster or a data- center).

The sequencer is made of three different stages for:

• the computation of dependency graphs;

• the computation of instructions sequences;

• the execution of instructions sequences.

Each stage can be called separately (in an incremental execution mode), or chained together (blackbox execution mode). Both modes have their use in real life. Incremental mode allows the end user to validate dependency graph and/or instructions sequence before putting it on production for its actual execution. This is done for an Emergency PowerOff (EPO) instructions sequence for example. The blackbox mode is used for simple usage such as powering on/off small subset of clusters or data centers.