Configuring a Replica Set: Reconfiguring or Removing

• How do you set "primary" or "secondary"?

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  • An up-to-date MongoDB instance with the
    highest priority setting will become the Primary

• How do you use rs.reconfig() to set the priority?

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  • View config: rs.conf()
  • Make a note of the _id number under members
  • Assign config to a variable: config = rs.conf()
  • Set the priority: config.members[X].priority=N
  • Where X is the member _id to change
  • and where N is the priority number
  • Reconfigure: rs.reconfig(config)

• How else can you use rs.reconfig()?

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  • Remove replica set members
  • Rename DNS or hostnames

• What has to be done before removing a member?

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  • Stop MongoDB on the replica set member to be removed
  • Disable the replSet setting in the mongod.conf file

• How do you use rs.remove()?

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  • Connect to the Primary
  • Use db.isMaster() to ensure the replica member is the Primary
  • Type: rs.remove("dns.address|hostname")
  • Or: rs.remove("dns.address|hostname:port")

• How do you force a member to become primary?

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  • From the mongo shell of the current primary: rs.stepDown(120)
  • From the mongo shell of the undesired secondaries: rs.freeze(120)
  • The remaining secondary will become primary
  • Alternatively:
  • use local
  • db.system.replset.update({_id:"rs0"},{$set:{members:[{_id:0,host:"HOSTNAME:27017"}]}})