Hey there,
I couldn’t find information in the documentation on what happens if I specify multiple mongos instances within the connection string, e.G.:
mongodb://mongos0.example.com:27017,mongos1.example.com:27017,mongos2.example.com:27017
Will all instances of my application connect to the mongos0.example.com instance, or will they randomly pick one, or how is the actual mongos instance being selected?
I am using mongoose which uses the latest mongo@3.6.0 node driver.
If there is more than one mongos instance in the connection seed list, the driver determines which mongos is the “closest” (i.e. the member with the lowest average network round-trip-time) and calculates the latency window by adding the average round-trip-time of this “closest” mongos instance and the localThresholdMS . The driver will load balance randomly across the mongos instances that fall within the latency window.
See more details here:
https://docs.mongodb.com/manual/core/read-preference-mechanics/#load-balancing
Best
Pavel