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2.5. Testing Your Configuration Changes

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 (e.g. crm_shadow --commit mytest --force), it is often advisable to simulate the effect of the changes with crm_simulate. For example:
# crm_simulate --live-check -VVVVV --save-graph tmp.graph --save-dotfile
This tool uses the same library as the live cluster to show what it would have done given the supplied input. Its output, in addition to a significant amount of logging, is stored in two files tmp.graph and Both files are representations of the same thing: the cluster’s response to your changes.
The graph file stores the complete transition from the existing cluster state to your desired new state, 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 [8] dot-file representing the same information.
For information on the options supported by crm_simulate, use its --help option.

Interpreting the Graphviz output

2.5.1. Small Cluster Transition

An example transition graph as represented by Graphviz
In the above example, it appears that a new node, pcmk-2, has come online and that the cluster is checking to make sure rsc1, rsc2 and rsc3 are not already running there (Indicated by the rscN_monitor_0 entries). Once it did that, and assuming the resources were not active there, it would have liked to stop rsc1 and rsc2 on pcmk-1 and move them to pcmk-2. However, there appears to be some problem and the cluster cannot or is not permitted to perform the stop actions which implies it also cannot perform the start actions. For some reason the cluster does not want to start rsc3 anywhere.

[8] Graph visualization software. See for details.