For Restful servlet (org.apache.hadoop.hbase.rest.Main (0.94), org.apache.hadoop.hbase.rest.RESTServer (trunk)) on Jetty, we need to first explicitly start the service (% ./bin/hbase-daemon.sh start rest -p 8000 ) for application running. Here is a scenario, sometimes, HBase cluster are stopped/started for maintanence, but rest is a seperated standalone process, which binds the HBaseAdmin at construction method.
HBase stop/start cause this binding lost for existing rest servlet. Rest servlet still exist to trying on old bound HBaseAdmin until a long time duration later with an "Unavailable" caught via an IOException caught in
such as RootResource.
Could we pairwise the HBase service with HBase rest service with some start/stop options? since seems no reason to still keep the rest servlet process after HBase stopped? When HBase restarts, original rest service could not resume to bind to the new HBase service via its old HBaseAdmin reference?
So may we stop the rest when hbase stopped, or even if hbase was killed by acident, restart hbase with rest option could detect the old rest process, kill it and start to bind a new one?
From this point of view, application rely on rest api in previous scenario could immediately detect it when setting up http connection session instead of wasting a long time to fail back from IOException with "Unavailable" from rest servlet.
Put current options from the discussion history here from Andrew, Stack and Jean-Daniel,
1) create an HBaseAdmin on demand in rest servlet instead of keeping singleton instance; (another possible enhancement for HBase client: automatic reconnection of an open HBaseAdmin handle after a cluster bounce?)
2) pairwise the rest webapp with hbase webui so the rest is always on with HBase serive;
3) add an option for rest service (such as HBASE_MANAGES_REST) in hbase-env.sh, set HBASE_MANAGES_REST to true, the scripts will start/stop the REST server.