I am of the same opinion as Howard. Quiz with 600 concurrent users and 2000 other aktive users are a heavy load. Independently of how many virtual machines you put together their total power is never more than the power of the engine pulls them all, meaning the hardware. In fact they are less. Firstly because of the additional layer of virtualization. Secondly the overhead needed to join the machines together - clustering I mean.
That is in general. Specifically to your case 2 core / 4 GB RAM machines are small! OK, yourDB server
has 12 GB. But for the DB the disk I/O is the critical parameter. And then the NFS for moodledata? It is good for big, slow files. But not for what Moodle demands from its moodledata.
I repeat what I always say here: Those 2600 users won't start batting from one day to the other. Start with a good state-of-the-art dedicated machine. Put lot of RAM, get a very good disk and start as a single server. Do a good installation, Linux is good, try Nginx and PostgreSQL
. Closely monitor the demand on the machine, tune and upgrade as needed. If you have a simple installation, you won't be reluctant to change it. Contrary to the common belief here, migrating Moodle is simple, unless you are entangled in a complicated architecture.
I noticed that you are a veteran from Moodle 1.4 times. Well that is a plus and a minus. The power demand of Moodle has exploded since then! (Well, it does a whole lot more. ;)) Read the performance recommendations linked in the header of this forum. Read/search past discussion. Here are some recent and related ones:
- Moodle 3.7 Quiz for 15000 concurrent users via Mobile App? Is it possible?
- I/O File Performance
- Hardware /performance suggestion
- Help! Database server CPU maxed out
and many more.