docs: Document multiple app approach

docs/Guides/Recommendations.md

@@ -8,6 +8,7 @@ This document contains a set of recommendations when using Fastify.
   - [HAProxy](#haproxy)
   - [Nginx](#nginx)
 - [Kubernetes](#kubernetes)
+- [Running Multiple Instances](#multiple)
 
 ## Use A Reverse Proxy
 <a id="reverseproxy"></a>
@@ -298,3 +299,19 @@ readinessProbe:
     timeoutSeconds: 3
     successThreshold: 1
     failureThreshold: 5
+```
+
+## Running Multiple Instances
+<a id="multiple"></a>
+
+While [Use A Reverse Proxy](#use-a-reverse-proxy) explains why 
+multiple Fastify apps on the same server should not be used for horizontal
+scaling purposes, there are several use-cases where running multiple apps 
+would be a recommended approach. Most common examples would be exposing
+healthcheck and metrics endpoints on a separate port, in order to prevent 
+public access.
+
+It is perfectly fine to spin up several Fastify instances within the same 
+Node.js process and run them concurrently, even in the heavy load systems. 
+Each Fastify instance only generates as much load as the traffic it receives,
+plus the memory used for that Fastify instance.