We saw previously how to make a series of changes to a "shadow" copy of the configuration. Before loading the changes back into the cluster (eg. crm_shadow --commit mytest --force), it is often advisable to simulate the effect of the changes with crm_simulate, eg.

# crm_simulate --live-check -VVVVV --save-graph tmp.graph --save-dotfile tmp.dot

The tool uses the same library as the live cluster to show what it would have done given the supplied input. It’s output, in addition to a significant amount of logging, is stored in two files tmp.graph and tmp.dot, both are representations of the same thing — the cluster’s response to your changes.

In the graph file is stored the complete transition, containing a list of all the actions, their parameters and their pre-requisites. Because the transition graph is not terribly easy to read, the tool also generates a Graphviz dot-file representing the same information.