1000 users to do a quiz on Moodle is a huge amount. I have worked on Moodle platforms with 1,000,000 users in Spain and never did 1000 users ever simultaneously do a quiz. That said, Moodle quizzes are very server intensive and do require a lot of server resources.

Recently we were having issues with Moodle quizzes with around 800 concurrent users and we had 8 webserver with x 4CPU Xenon’s, each with 32GB of Ram and 4 X Mysql, clustered with the same processors and RAM

As you can see, Moodle isn’t great with the Quiz Module

Using Chamilo (there’s an image in the D.O. marketplace) should enable you to do that with 2 web servers of ~8vCPUs, 1 DB server of ~16vCPUs (might double that for fail-over redundancy), one shared space, one memory server for PHP sessions, and one load balancer service from D.O.

We successfully used a slightly higher infra for 2500 simultaneous users, although with version 1.11.12 of Chamilo, which is slightly optimized (in comparison to 1.11.10).

Setting up the infra can be slightly challenging if you never did that, though (but it would be for Moodle too). You could get away with one 16vCPU VM for the web server and avoid the duplication and redundancy of the setup, but I feel safer having the whole setup balanced.