MongoDB replica set — 7 steps to set up high availability cluster

A MongoDB replica set is a group of mongod processes that maintain the same dataset across multiple servers. It provides automatic failover: when the primary node becomes unavailable, the remaining members elect a new primary and the cluster keeps running. This is the baseline for any production MongoDB deployment that needs to survive hardware failures or unexpected restarts. Setting one up takes maybe an hour if you've done it before. If you haven't, the main traps are misconfigured hostnames, firewall rules that silently block inter-node traffic and skipping the failover test at the end. This guide covers each step in order. What is a replica set A replica set has one primary, one or more secondaries and optionally an arbiter. The primary handles all writes. Secondaries replicate from the primary using an oplog and can serve reads if configured to do so. An arbiter participates in elections but stores no data — it exists purely to provide an odd number of votes without the cost of a