How does MongoDB ensures high availability?

0-2 years experience

1. 1You have a MongoDB replica set with three nodes. If the primary goes down, what steps does MongoDB take to keep the application running?
2. 2How would you configure read preference so that reads continue during a primary failure?
3. 3What happens to client connections when the primary steps down?

2-5 years experience

1. 1We observed increased latency after a primary election in our replica set. What could cause that and how would you troubleshoot?
2. 2Explain why using a write concern of 'majority' might delay acknowledgments during a failover, and how you'd mitigate it.
3. 3If a secondary falls behind the oplog during a network partition, how does MongoDB handle catch‑up after the partition heals?

5-8 years experience

1. 1Design a high‑availability deployment for a globally distributed e‑commerce platform using MongoDB. Discuss replica set placement, election settings, and read/write concerns to balance latency and durability.
2. 2During a rolling upgrade of a sharded cluster, how would you ensure continuous availability while nodes are restarted?
3. 3What are the trade‑offs of using an arbiter versus a hidden secondary for elections in a three‑node replica set?

8+ years experience

1. 1Our organization is migrating from a single‑region MongoDB deployment to a multi‑region active‑active architecture. What architectural changes are required to preserve high availability and data consistency, and how would you address cross‑region latency?
2. 2How would you set up automated monitoring and self‑healing for replica set elections across multiple data centers to meet a 99.99% SLA?
3. 3When integrating MongoDB with a legacy relational system, how would you design a data synchronization strategy that respects MongoDB’s HA mechanisms without introducing split‑brain scenarios?