[true_religion]

You want staging to be as close to production as possible, but obviously not exactly he same size.

If you spend 1M on production, you might have a staging environment 1/10th of that size. Say 10 machines in a cluster instead of 100. But some technologies also have minimum implementation cost requirements per tier of usage. Like if you have a multiple data centers in production, you will need to test that in staging. You can’t just have 1 machine in a cluster, so your staging environment needs at least 3 to make a quorum. Therefore, to have 5 data centers in staging, you now need 15 machines... which is more than the base of 1/10th of production.

Issues like that can balloon staging costs if you try to properly implement it.

[fastball]

Honestly with the right architecture you shouldn't even need 10 machines in a cluster, 2 should do. After all, the whole point of clusters/load-balancing etc. is that 2 machines behind your LB should function the same as 1000 machines behind your LB, just the latter gives you a lot more throughput.

[LoSboccacc]

it depends however whether you want to test the code or the infrastructure

my preproduction uses a three machines setup so it can catch clustering problems, but the code itself can run just as well on a single machine interacting with a local single instance db, and devs run it like that.