[0] https://www.nomadproject.io/docs/install/production/requirem...
Hashicorp is doing a smart but normal thing for on-prem sizing there - they are recommending specs which ensure you have no problems for a lot of workload sizes. And "workload" can grow very large there, since a single DC can handle up to 5k clients and such.
IIRC both k8s and nomad rely on the Raft algorithm for consensus, and so both of them inherit the requirement of a minimum of 3 nodes from that algorithm.
If you want something to run some containers in the cloud, and you aren't concerned by the occasional failure, then there is no issue running a single Nomad (or k8s) on a single machine and later adding more if and when you require it.
And yes, nomad recommends 3 - 9 nodes in prod, maybe 11 or 13. The 3 are necessary to be able to tolerate one broken/maintained node and maintain the ability to schedule workloads.
You can increase the number of tolerated nodes by increasing the number of nodes - 5 tolerate 2, 9 tolerate 3, 11 tolerate 5, 13 tolerate 6, but raft becomes slower with more nodes, because raft is a synchronous protocol.
However, it is entirely possible to run a single node nomad system, if the downtime in scheduling is fine.
We run a Raft cluster of 5 voting members with 13,000 physical Nomad nodes mixed across OS's with a bunch of random workloads using docker, exec, raw_exec, java, and some in-house drivers. I'll clarify that (and I can't... because I can't edit my post anymore :( ).
We're nowhere near that size, but the architecture is probably identical.
We started out with a three-node cluster using the smallest (1 vCPU/2GB RAM) VM you can get. Our initial requirement was to be able to do zero-downtime deployments and have a nice web UI to perform them (alongside the other advantages you get from a distributed system). We have now rescaled them to the next tier (2 vCPU/4GB RAM).
The hardware requirements depend on your workload. We process about 200 requests/sec right now and 600-700 per second on Saturdays (due to a larger client) and the nodes handle this load perfectly fine. All our services are written in Go and there is a single central Redis instance caching sessions.
Our database server is not part of the cluster and has 32 physical cores (64 threads) and 256GB RAM.
I say start out small and scale as you go and try to estimate the RAM usage of your workloads. The HashiStack itself basically runs on a calculator.
It, of course, depends entirely on your use case and workload.
I have a few dozen jobs running with what I think is a pretty decent mix/coverage. I've got a bunch of services, some system jobs, half dozen scheduled jobs, etc, etc.
I'm running my cluster with 3x "master" nodes which act as the control plane for nomad and consul as well as run vault and fabio (for ingress/load balancing). I have three worker nodes running against this that are running consul and nomad agents as well as my workloads.
The control plane nodes are currently sitting on AWS's t3.nano instances. `free` shows 462MB total RAM with 100MB available. Load average and AWS monitoring show CPU usage within a rounding error of 0%.
If this were in a professional capacity I probably wouldn't run it this close to the wire, but for personal use this is fine--it will be quite easy to upgrade the control plane when or if the time comes.