Running multiple bitcoin instances on same server system I wish to run multiple instances of bitcoind on my server to support highly read intensive RPC applications. 

Following links:

how to run multiple bitcoind node on one server?

Running Multiple Full Nodes on one Host

Is it possible to run more than one client instance on a machine?

How do I run two instances of bitcoind on the same linux machine with different conf files?

suggests that by using different conf file and data dir we can run multiple instances.

However, my doubt is that since in each case, we are specifying different config file and data dir to same binary bitcoind, e.g.

bitcoind -datadir=./bitcoinNode1/ -conf=./bitcoinNode1/bitcoin.conf
bitcoind -datadir=./bitcoinNode2/ -conf=./bitcoinNode2/bitcoin.conf
bitcoind -datadir=./bitcoinNode3/ -conf=./bitcoinNode3/bitcoin.conf


Does same single binary bitcoind is going to handle request for all instances (bitcoinNode1, bitcoinNode2, bitcoinNode3)? In such case load will be on single binary and I have a doubt for performance gain.

Or is it better to create different binaries bitcoind1, bitcoind2 etc. for each config+data_dir combo?

Thanks.
The provided approach is correct.

A binary itself does not handle any requests. When you run bitcoind with separate instances of the config and data directories, the system will create multiple instances of the bitcoind program to execute. Each of these instances is a fully independent bitcoin node, and has no relation to any other instance running on that machine.

Copying the binary will make no difference.