Replica Set Troubleshooting

• What if you have two primaries?

  .
  
  

  • You can run rs.initiate() ONLY on the first member of the replica set!
  • On the secondary which acts like a primary, clear the folder indicated by dbpath
  • Restart the secondary

• What if the primary can "see" the secondary,
  but not the other way around?

  .
  
  

  • Run rs.conf() and make sure all servers can access all hostnames
  • Check firewall settings

• What about firewall settings?

  .
  
  

  • You need to allow an exception for MongoDB
  • Messages you might see when attempting to sync:
  • SELinux: security alert
  • Windows: Windows Firewall alert

• What if replicas are not syncing?

  .
  
  

  • FIRST: run rs.conf()
  • Make sure all hostnames are entered into DNS
  • or in the local "hosts" file of all computers in the replica set
  • THEN TRY:
  • ping hostname|DNS name
  • mongo --host hostname|DNS name --port 27017
  • Correct any communcations errors

• What if you have only one secondary?

  .
  
  

  • use local
  • db.system.replset.update({_id:"XXX"},{$set:{members:[{_id:0,host:"HHH:27017"}]}})
  • Where "XXX" is the replica set ID
  • and "HHH" is the hostname of the secondary
  • Restart MongoDB

• How can you get more information?

  .
  
  

  • docs.mongodb.org/manual/tutorial/troubleshoot-replica-sets/