Make Priority 0 Members PRIMARY?

[Carlos]

My replset is as follows:

1. PRIMARY = mongo1

2. SECONDARY = mongo2

3. SECONDARY = mongo3

4. SECONDARY / Priority 0 = mongo4

5. SECONDARY / Priority 0 = mongo5

My question is now that I have successfully added mongo4/5 to the replset as priority 0 members, how to I force mongo4 or mongo5 to become PRIMARY?

1-3 = NYC, NY

4-5 = Atlanta, GA. 

If the NY data center does go down, how could I force my priority 0 members to be elected as PRIMARY? I can assume I would need to 1st change the priority of the mongo4,5 nodes from 0 and then force an election but how can I force a specific instance to be isMaster()?

Thanks for any info!

[Žygimantas Stauga]

1-3 / Change priority to: 10

4-5 / Change priority to: 1

[Alex Penazzi]

Hi Carlos,

you have different way to do this, but keep in mind that the highest is the priority, the highest is the possibility that the node become primary.

I do not know which mongodb version you are using, but according with this:

https://docs.mongodb.com/manual/tutorial/adjust-replica-set-member-priority/

you should setup priority highest number to the node it should become primary

best

alex

[Aly Cabral]

Hi Carlos,

As the other answers address, the priority value of 0 suggests that you never want that node to become primary in any case. However in your use case, you would want to make sure you have a majority when electing a new primary. In your current topology, with only two nodes in the second data center, a majority cannot be achieved if the NY data center goes down. See also Replica Set: fault tolerance. You could do something like this however:

Priority 10: mongod1, mongod2, mongod3 - NYC, NY

Priority 1: mongod4, mongod5, mongod6 - Atlanta, GA
arbiter - hosted on AWS (or the cloud flavor of your choosing somewhere else not in Atlanta or NY). 

An arbiter does not hold any data, but is allowed a vote in an election for primary. The arbiters default priority is 1 but it can never be elected primary. But an arbiter does allow you to get a majority if either of your datacenters in NY or GA goes down. Another optional topology is adding two additional host arbiters to your current setup:

Priority 10: mongod1, mongod2, mongod3 - NYC, NY
Priority 1: mongod4, mongod5 - Atlanta, GA
arbiter1, arbiter2 - hosted on AWS (or the cloud flavor of your choosing somewhere else not in Atlanta or NYC).

Hope that helps. Let me know if you have any other questions!

Aly