Sizing a session broker: the unit is concurrent sessions, and the bottleneck is not the CPU

Disclosure: the numbers below are from Tessera, which I work on. The reasoning applies to any proxy that sits in a session path. Every vendor page in this category says something like "scales to thousands of users". It is a useless number, because a user who is not connected costs nothing. What costs something is a session that is open right now. So here is the arithmetic instead, with the method, so you can check it against whatever you are evaluating. The unit The controller does not know how many engineers you employ and does not care how many targets are registered. It knows how many sessions are open. The planning rule that has held up for us: on a normal working day, 10–20% of a team is connected at once. A 200-person engineering organisation is 20–40 concurrent sessions, not Size for your own observed peak, but if you are estimating from scratch, start there. This matters because the difference between the two numbers is the difference between a 512 MB VM and an argument about whether you need a cluster. Memory A proxied session is mostly buffers. In our case: about 256 KB of copy buffers, plus 6 to 10 goroutines at roughly 8 KB of stack each. Call it 320 KB per session. The base Go process is about 30 MB. So 200 concurrent sessions is 200 × 320 KB ≈ 64 MB of live data, plus 30 MB base, ≈ 94 MB. Except that is not what RSS will show you, and this is the part people get wrong when they size Go services. Go does not hand memory back to the operating system promptly, and at the default GOGC=100 the collector lets the heap grow to roughly twice the live set before collecting. So resident memory settles at about double the arithmetic. Concurrent sessions vCPU Expected resident Provision up to 50 1 ~90 MB 512 MB 50–200 2 ~190 MB 1 GB 200+ 4 ~380 MB 2 GB The gap between the last two columns is headroom for spikes, not a hidden cost. A controller serving 200 sessions really does use a couple of hundred megabytes. Our Helm chart ships requests: 256Mi and limits: 1Gi ,