How many processors do I need to allocate to the fstify service in docker/k8?

[budarin]

💬 Question here

Fastify uses pino, which is implemented as a worker and therefore requires additional processor time

Based on your experience, how much CPU should be allocated for a service written in fastify?

PS: I haven't found any information about this anywhere

[mcollina]

I normally recommend allocating at least two (virtual) processors per Node.js processes to have the best latency. This advice is not relevant per Fastify or Pino.

[budarin]

Do I understand correctly that this recommendation concerns a simple application on node.js without worker and worker require an additional CPU?

[Uzlopak]

They always say that node is single threaded, but node can utilize a second cpu core.

So if you give node a second core, it will run faster than single core.

[budarin]

Thanks, I realized that for any simple node.js app requires at least 2 virtual processors - I understood that

But my question is related to the use of a worker (and in this case pino): is it necessary to allocate another virtual processor for it, or will two processors be enough for an application on fastify?

[jsumners]

will two processors be enough for an application on fastify?

You must make your own determination based upon your application's requirements. Review https://www.youtube.com/watch?v=P9csgxBgaZ8

[mcollina]

The second vcpu will mostly be used by the GC and libuv threadpool. Note that this is to minimize the latency for your users as well as memory usage as the GC fan run more frequently. The main thread won't have to stop to let the GC run.

It's totally fine to run node with 1 vcpu too.

[L2jLiga]

It's totally fine to run node with 1 vcpu too.

I can confirm that, for most of my application 1vCPU was enough and for some of them (e.g. API gateway) we've allocated less, about 100m-200m cpu in kubernetes

[kibertoad]

@mcollina This whole thread is useful information that deserves to be preserved. Can I create a PR to fastify, even though it is accurate not just for fastify?

[mcollina]

Sure thing, go ahead!

[kibertoad]

@mcollina Would you say that running pino in a separate worker thread affects the recommendation in any way, or "1 vCPU when optimizing for a throughtput, 2 vCPU when optimizing for latency" is still a good rule of a thumb?

[mcollina]

The new main reason to have 2 vpcus is to have one where the V8 gc could run.
Pino would hardly matter in that case.

note that pino won’t use a worker_thread by default, so this recommendation depends heavily on what the pino transport does.

[kibertoad]

@mcollina If we assume the pino transport simply writes to stdout (as this is the most popular option in k8s world), would using a worker-thread be recommended? And how would that affect the recommendation?

[mcollina]

If you just aim to write to standard out, don't use a pino transport.