Let's Understand Storm - Real-time Analytics with Storm and Cassandra - page 15

Delving into the internals of Storm
Now that we know which physical components are present in a Storm cluster, let's under-
stand what happens inside various Storm components when a topology is submitted. When
we say topology submission, it means that we have submitted a distributed job to Storm
Nimbus for execution over the cluster of supervisors. In this section, we will explain the
various steps that are executed in various Storm components when a Storm topology is ex-
ecuted:
• Topology is submitted on the Nimbus node.
• Nimbus uploads the code jars on all the supervisors and instructs the supervisors to
launch workers as per the NumWorker configuration or the
TOPOLOGY_WORKERS configuration defined in Storm.
• During the same duration all the Storm nodes (Nimbus and Supervisors) constantly
co-ordinate with the Zookeeper clusters to maintain a log of workers and their
activities.
As per the following figure, we have depicted the topology and distribution of the topology
components, which are the same across clusters:
In our case, let's assume that our cluster constitutes of one Nimbus node, three Zookeepers
in a Zookeeper cluster, and one supervisor node.
By default, we have four slots allocated to each supervisor, so four workers would be
launched per Storm supervisor node unless the configuration is tweaked.