Comment by Justin Njoh on "Need some help with MongoDB replica sets - Is it possible for Primary Mongo instance to become secondary automatically?"

CommentNeed some help with MongoDB replica sets - Is it possible for Primary Mongo instance to become secondary automatically?

Justin Njoh

MVPs & POCs on NoSQL DBs - why not ?

Dec 10, 2015

Hi Robert, That any member of a replica set (that is not configured as an arbiter) can become a primary is quite normal and there is nothing to worry about. If the current primary became unreachable for whatever reason (network issues, downtime, etc) a 'voting' process takes place to determine which of the secondaries becomes the primary. And when the previous primary became available, it would become a secondary.

This is all done transparently to the application ... and the driver should always connect to the current primary.

Justin Njoh

MVPs & POCs on NoSQL DBs - why not ?

Dec 14, 2015

Hi, an arbiter is a replica set member that doesn't store data and hence can never become a primary. So the main reason to have an arbiter is to economise on space, which reduces redundancy. I can see a hosting company doing this, and offering a 3-member replica where in fact only 2 members store data - but is this what you want ? Personally, I'd have all 3 members storing data.

Thanks a bunch Justin! Quick question - Is it recommended to have an arbiter if we have a 3 member replica set with one primary and two secondaries?

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