Can’t config replica set using MongoDB 3

This is an older question, but some important things to provide are:

• What version of MongoDB are you running?

• Can each server in the cluster communicate to every other server in the cluster on the assigned port (27018)? This includes the database shards and the mongos (balancer).

• The shards have to talk amongst themselves to replicate the data, and since the Sending and Receiving nodes are in different zones, are they in the same security group? Are there local firewalls preventing communication?

• Consider inspecting the amount of open file descriptors for the mongod process on each server. There is a hard max of 20k enforced in the server code, but typically there is another limit in place. Here's some commands to help:

  lsof -p <pid of mongod> | wc -l
  
  su - mongod # or whatever user mongod is running as
  ulimit -n # => some systems default to 1024
  

There are two questions here, one for MS clustering, and another one for Mongo.

MS Clustering

The decision of where to put the public, heart-beat, inter-node communication, and quorum drive is significant. Also cluster architecture makes a difference; you pick different quroum options if the two nodes are in adjacent racks than if they were in completely different datacenters.

Put the heartbeat on the same interface/subnet as the public interface

This theory holds that if you lose your public interface, you want the heartbeat to fail because this node is effectively down to users.

Put the heartbeat on it's own private interface/subnet

This theory holds that something outside of the cluster is arbiting who is doing what role, and unnecessary node-death is to be avoided.

Put the WFS on the heartbeat network

If the two nodes are in the same overall network (the same set of switches is supporting the non-public networks for both nodes) then putting the WFS on the heartbeat network doesn't introduce any new vulnerabilities.

If the two nodes are in different network fault domains (such as different datacenters), this is a bad idea. The heartbeat network provides the 'node majority' quorum option, and the WFS provides the 'File Share Majority' quorum option. You really want both options to be in separate fault domains.

Your revised diagram makes sense if both nodes are in the same data-center, though I myself would but the heartbeat on the public side.

MongoDB

MongoDB is a bit simpler. With even numbers of nodes, you absolutely want a third node to act as tie-breaker. They're pretty clear about that. However, your diagram states:

Up to 12 replica members (7 can vote).

7 is an odd number. You don't require an Arbiter.

Unlike Microsoft clusters, Mongo's cluster voting doesn't care about multiple avenues of network to break voting deadlocks. Because of this, separate arbitration and cluster-internal networks do not provide any meaningful increase in robustness. The only reason you'd want a separate arbitration network is if replication traffic was expected to be so heavy that election-packets (the heartbeat, actually) would get pushed so far down the stack that it would miss the 10 second timeout.