HBASE SHELL: Logic behind "ZK cluster client port has to be the same as default port in config"

[Stephen Jiang]

In hbase shell code, the following *HMasterCommandLine#startMaster* code
logic has been in the code forever :-).  I just wonder what is the logic
behind it & why it is the case for the error message ("shell will not be
able to find this ZK quorum").

- start zookeeper cluster and return the active ZK server port

- *the return port has to be the same as the default port in the config;
otherwise, throw exception*

- set the default port in configuration to be the return port (why, looks
redundant to me? - if this is not redundant, then after updating the
config, should SHELL be able to find the ZK quorum? - my testing show not,
but I could not figure out reason behind it.)


Here is the code:

        int zkClientPort = conf.getInt(HConstants.ZOOKEEPER_CLIENT_PORT, 0);

        if (zkClientPort == 0) {

          throw new IOException("No config value for "     +
HConstants.ZOOKEEPER_CLIENT_PORT);

        }

        ...

        int clientPort = zooKeeperCluster.startup(zkDataPath);

        if (clientPort != zkClientPort) {

          String errorMsg = "*Could not start ZK at requested port of " +*

*            zkClientPort + ".  ZK was started at port: " + clientPort +*

*            ".  Aborting as clients (e.g. shell) will not be able to find
" +*

*            "this ZK quorum.*";

          System.err.println(errorMsg);

          throw new IOException(errorMsg);

        }

        conf.set(HConstants.ZOOKEEPER_CLIENT_PORT,

                 Integer.toString(clientPort));