[eyberg]

It depends. A t2.nano has 512mb of memory. If you are using Go or something like that you could go much lower but any runtime environment such as ruby/python/node are going to want a minimum of a few hundred meg. If you are using the JVM you most definitely are going to want an instance with much more memory.

At the end of the day your application decides how much memory it wants and the sysadmin/SRE/devops person just ensures it has enough so it doesn't crash.

If you are hosting your own workloads and those workloads only need tens of megs of ram than you can pack as much as your hypervisor can handle.

Alfred talks about booting 110,000 vms on one host before memory exhaustion:

https://ieeexplore.ieee.org/document/6753801