Improve on the Middlemanager-less documentation #18791
Description
I have recently migrated my druid cluster to middlemanager-less and it was comparibly painfull.
One of the main issues is that even though the doc page for middlemanager-less contains already quite a lot of information, it is still not enough for a production grade cluster (or data wise big SDLC cluster).
Something that i discovered is that the extra.jvm.options (set via druid operator) don't work.
This seems related to the fact that the peon.sh script seems to search for a jvm.options file that does never exist when using the druid-operator.
The file existing when using the druid-operator is /opt/druid/conf/druid/cluster/master/coordinator-overlord/extra.jvm.options.
The file it seems to be searching to patch is /tmp/conf/druid/cluster/master/coordinator-overlord/jvm.config.
This becomes an issue when trying to set either of: XMS/XMX/XX:MaxDirectMemorySize.
To still apply these settings, I do now set JAVA_OPTS="-Xms256m -Xmx6g -XX:MaxDirectMemorySize=1g" which works fine so far, but wasn't very intuitive when there is a DRUID_XMS, DRUID_XMX and DRUID_MAXDIRECTMEMORYSIZE env var mentioned in the script.
All of how this is intended to be used should become part of the docs. Ideally the original author adds it.