The worker is the following component, which is started after master nodes, and it's bootstrapped to form a distributed Spark cluster. You can start a standalone worker server by executing the following:
$SPARK_HOME/sbin/start-master.sh -h 127.0.0.1 spark://127.0.0.1:7077
Once it starts, check the master's web UI. You should see a new worker node added to it and listed under the worker section, along with its instance configuration idle on the OS. This new worker node will be hyperlinked to redirect to the worker web UI, and can be navigated to with the following URL (http://127.0.0.1:8081):
Figure 9.3: Worker web UI
