MongoDB Arbiter AWS EC2

Question

Trying to figure out what kind of machine to requisition for a MongoDB Arbiter so I can set up a replica set. All it needs to do is vote when a machine goes down, right? Could there possibly be any problem with using a micro EC2 instance for this?

Answer 1

I would not use Amazon Micro for an Arbiter as Micro instances can have long lags in processing which could trigger the replication threshold for non-response. In this case you will go into Secondary only ready only mode and your app can't do any writes as once the arbiter has voted it can't revote.

Go with at least m1.small as you are guaranteed computing power or as someone else suggested throw it as a share on another instance.

Please be advised that sharing with other instances complicates your error troubleshooting so it's much easier to just put it on it's own instance.

FYI - We run mongo replicaset for mission critical app on EC2 with arbiter and have also worked with Mongo consultants to come to this conclusion.

Answer 2

You are correct - Arbiters are nodes in a replica set that only participate in elections. Further information can be found here:

http://www.mongodb.org/display/DOCS/Adding+an+Arbiter

A micro EC2 instance should be fine for this if you do need one. .