private static void emitPerNodeDiffEvents(final PerStateParams params, final List<Event> events) {
        final ContentCluster cluster = params.cluster;
        final ClusterState fromState = params.fromState.getClusterState();
        final ClusterState toState = params.toState.getClusterState();

        for (ConfiguredNode node : cluster.getConfiguredNodes().values()) {
            for (NodeType nodeType : NodeType.getTypes()) {
                final Node n = new Node(nodeType, node.index());
                emitSingleNodeEvents(params, events, cluster, fromState, toState, n);
            }
        }
        emitNodeResourceExhaustionEvents(params, events, cluster);
    }
Responsible for inferring the difference between two cluster states and their
state annotations and producing a set of events that describe the changes between
the two. Diffing the states directly provides a clear picture of _what_ has changed,
while the annotations are generally required to explain _why_ the changes happened
in the first place.

Events are primarily used for administrative/user visibility into what's happening
in the cluster and are output to the Vespa log as well as kept in a circular history
buffer per node and for the cluster as a whole.
clustercontroller-core/src/main/java/com/yahoo/vespa/clustercontroller/core/EventDiffCalculator.java