int getAvailableConnectionsCount() {
    int count = 0;
    for (HostPortPoolManager hostPortPoolManager : hostPortToPoolManager.values()) {
      count += hostPortPoolManager.getAvailableConnectionsCount();
    }
    return count;
  }
Return the total available connections across all {@link HostPortPoolManager}s.
@return total established and available connections.
ambry-network/src/main/java/com/github/ambry/network/ConnectionTracker.java