public int getLeaderRegionCount() {
        int count = 0;
        for (final RegionEngine regionEngine : this.regionEngineTable.values()) {
            if (regionEngine.isLeader()) {
                count++;
            }
        }
        return count;
    }
Storage engine, there is only one instance in a node,
containing one or more {@link RegionEngine}.

@author jiachun.fjc
jraft-rheakv/rheakv-core/src/main/java/com/alipay/sofa/jraft/rhea/StoreEngine.java