docs: Add section about capacity planning

docs/Guides/Recommendations.md

@@ -8,7 +8,8 @@ This document contains a set of recommendations when using Fastify.
   - [HAProxy](#haproxy)
   - [Nginx](#nginx)
 - [Kubernetes](#kubernetes)
-
+- [Kubernetes](#kubernetes)
+- [Capacity planning for production](#capacity)
 ## Use A Reverse Proxy
 <a id="reverseproxy"></a>
 
@@ -298,3 +299,28 @@ readinessProbe:
     timeoutSeconds: 3
     successThreshold: 1
     failureThreshold: 5
+```
+
+## Capacity planning for production
+<a id="capacity"></a>
+
+In order to rightsize your fastify application deployment in production, the 
+following considerations need to be taken into account:
+
+* In order to have the lowest possible latency, 2 vCPU are recommended per app 
+instance (k8s pod). The second vCPU will mostly be used by the GC and libuv
+threadpool. This will minimize the latency for your users, as well as the
+memory usage, as the GC will be run more frequently. The main thread won't
+have to stop to let the GC run.
+
+* In order to optimize for throughput (handling the largest possible amount of
+requests per second per vCPU), consider using smaller amount of vCPUs per app 
+instance. It is totally fine to run Node.js application with 1 vCPU.
+
+* You may experiment with even smaller amount of vCPU, which may provide even 
+better throughput in certain use-cases. There are reports of e. g. API gateway
+solutions working well with 100m-200m vCPU in Kubernetes.
+
+See [Node's Event Loop From the Inside Out ](https://www.youtube.com/watch?v=P9csgxBgaZ8)
+in order to understand the workings of Node.js in greater detail and make a
+better determination about what your specific application needs.