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  1. Core Server
  2. SERVER-11776

Replication 'isself' check should allow mapped ports

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    Details

    • Type: Bug
    • Status: Closed
    • Priority: Major - P3
    • Resolution: Fixed
    • Affects Version/s: 2.4.10, 2.6.1
    • Fix Version/s: 2.6.4, 2.7.2
    • Component/s: Replication
    • Labels:
      None
    • Backwards Compatibility:
      Fully Compatible
    • Operating System:
      ALL
    • Backport Completed:

      Description

      'isself' should match the ports only if the hosts are being string matched. In cases where an instance is being addressed through a proxy port, port matching is an incorrect check - it invalidates a genuine match.

      e.g. a mongod instance listening on port 27017 may be get redirected traffic from another port through IPtables routing. Such instances would fail to get added to a replica set for no good reason. Port proxies maybe required in multi-tenant cloud based systems where bind-able IPs/ports are NAT'ed.

      Take this example replica set config to setup a one node cluster. The server itself can be addressed using a DNS name and an externally proxied port, but we cannot form a cluster if the same is used for the rs config.

      config = { 
                      "id"             : "test", 
                      "members" : [ { 
                                               "_id" : 0, 
                                               "host" : "public_dns_to_ec2_node:38132" 
                                              } ] 
                      }

      Internally, the mongod was bound to 127.0.0.1:27017 and we have IPtables proxy rule to route all tcp traffic from 38132 to 127.0.0.1:27017, e.g.

      -A OUTPUT -d 10.203.77.175/32 -m tcp -p tcp --dport 38132 -j DNAT --to-destination 127.0.0.1:27017
      -A PREROUTING -d 10.203.77.175/32 -m tcp -p tcp --dport 38132 -j DNAT --to-destination 127.0.0.1:27017

      where 'public_dns_to_ec2_node' routes to 10.203.77.175 through public IP DNS registration.

      With the above example it is clear that a fix is needed to not unnecessarily match the ports as integers. Or we cannot even create a one node cluster, leave aside a usable 3-node replica set.

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                  Updated:
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