Configuring a Replica Set: Adding a Secondary

• How do you start?

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  • Make sure MongoDB is installed but stopped
  • Add an entry to DNS or the local "/etc/hosts" file to identify all replica hosts
  • Example: mongo0rs0.company.com, mongo1rs0.company.com, etc.
  • Ensure that the secondary can connect to the primary

• How many MongoDB instances should go into a set?

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  • A minimum of 3 is recommended:
    1 primary and 2 secondaries
  • Maximum of 7 "voting" members
  • Add as many non-voting members as desired
  • Set priority=0 to make a member non-voting

• How do you configure the mongod.conf file?

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  • Set the parameters as appropriate to your system
  • Comment out bind_ip to allow MongoDB to respond to all network cards
  • You must configure the replSet parameter
  • Example: replSet=rs0
  • Do not set priority here!
  • Master/Slave configuration is not recommended: use replica sets

• How do you initialize the secondary?

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  • Follow one of these strategies:
  • 1A backup the /data/db folder of the primary
  • 1B restore to the /data/db folder of the secondary
  • OR 2A remove all files and folders from the /data/db folder of the secondary

• What needs to be done on the primary?

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  • Add an entry to DNS or the local "/etc/hosts" file to identify the secondaries
  • Example: mongo1rs0.company.com, mongo2rs0.company.com, etc.
  • From the mongo command shell on the primary:
  • rs.add("dns.address|hostname")
  • Wait for the synchronization to occur

• How do you know the replica set is running?

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  • Access the mongo shell
  • The command prompt should reflect the status
  • View status: rs.status()
  • View config: rs.conf()