Research of Moodle cron performance improvement about moodle

[hosungsmsft]

We recently learned that Catalyst IT EU presented their experiences with Cron Queue at MoodleMoot UK/Ireland 2018 (search for "Cron Queue" after clicking the link). They mentioned that they'll be releasing their plugin for the feature and I think we should utilize that as well.

Setting the milestone for this to be v1.5.1 for planning, can be adjusted as needed.

[hosungsmsft]

As we discussed over the call, the status of Catalyst EU's cron plugin is not yet ready and we are converting this issue into a generic research/recommendation work item.

[hosungsmsft]

This issue is put on hold for now. Dropping the milestone.

[noveck]

If cron performance is an issue, I'd suggest decoupling the moodlecron from the user facing web servers.
An additional VM can be commissioned to deal specifically with integration/management which is outside of the webcluster. If this is deemed too complex, maybe repurpose the caching VM for double duty. Storage/Mem are pretty much the heavy hitters for caching, so the servers can be bumped up processing wise to manage the moodlecron.

[SorraTheOrc]

We already have a separate controller VM on which cron workloads run. This issue doesn't exist because of an observed problem, rather it exists because of a concern raised by a user. To date this concern has not been supported by an actual problem.

Note there is no cache VM. When a cache is desired we use Redid provided as an Azure service. This reduces cost and management overhead.