I am trying to rebalance the number of executors for a bolt in a running Apache Storm (0.9.5) topology. When I execute the command to the Nimbus node ./storm rebalance MyTopology -n 2 -e GreenBolt=4 it accepts the command line input but the number of executors is not changed when I view in the Storm UI.
Is there a limitation that I'm not aware of like a rebalance can not increase the total number of executors and only move them from one bolt to another?
You always need to have more (or equal number of) tasks than executors. As the number of tasks is fixed, you need to set a larger initial number than initial executors in order to be able to scale up the number of executors during runtime. You can see the number of tasks, as maximum number of executors:
#executors <= #numTasks
See here for details: https://storm.apache.org/documentation/Understanding-the-parallelism-of-a-Storm-topology.html
来源：https://stackoverflow.com/questions/31932573/rebalancing-executors-in-apache-storm