I want to ask that what is the minimum requirement(In terms of the number of P and PE routers required) if I want to connect my 5 data centers in different cities together by bulding my own MPLS backbone(my own cloud). This is just a private setup and we are not serving any clients. Currently the connectivity is via p2p E1 links.
if we want to be fault tolerant at each single failure event of node or link:
each datacenter has to be connected with two CE nodes to two different PE nodes.
if the datacenters are in different cities we can suppose you need two PE nodes per town (to build a minimal point of presence POP).
Two P nodes for fault tolerance.
PEx1 connects to P1 via WAN link.
PEx2 connects to P2 via WAN link.
eventually the P1 and P2 nodes can coexist with the PE role if there is a central site.
The P1 and P2 nodes can also act as BGP route reflector servers.
So I would say 10 PE nodes and two P nodes.
The underlying problem is that you can own your PE and P routers but you still need to buy WAN links from service providers to interconnect them.
And you should interconnect with at least DS3 links if possible to scale to future needs.
Hope to help