Suggest an editImprove this articleRefine the answer for “What is MongoDB's architecture made of?”. Your changes go to moderation before they’re published.Approval requiredContentWhat you’re changing🇺🇸EN🇺🇦UAPreviewTitle (EN)Short answer (EN)The core is the `mongod` process (storage, query handling, replication, sharding, security) on top of a Storage Engine (WiredTiger by default); a sharded cluster adds a `mongos` router and config servers holding metadata about how data is distributed. **Key point:** fault tolerance comes from a Replica Set (one primary for writes, several secondaries for reads and automatic failover), and horizontal scaling from a Sharded Cluster of shards, mongos routers, and config servers; on top of it all sit client drivers and tools like Ops Manager/Atlas.Shown above the full answer for quick recall.Answer (EN)ImageMongoDB's architecture consists of the following key components: ### 1. MongoDB Server (mongod) The main server process. Responsible for storing data, handling queries, replication, sharding, and security. Inside it live several subsystems: - *Storage Engine*, the storage module (WiredTiger by default) - *Query Processor*, query handling and optimization - *Replication Manager*, manages replication - *Sharding Router/Config*, the logic for distributing data across shards - *Journal/Write-Ahead Log*, the log used for fault tolerance ### 2. mongos (the router in a sharded cluster) A proxy process that routes the application's requests to the right shards, hiding the fact that data is distributed. ### 3. Storage Engine (e.g. WiredTiger) Responsible for the physical storage of data on disk, compression, cache management, and working with the journal and locks. ### 4. Replica Set A group of servers with one *primary* (writes go to it) and several *secondaries* (hold copies and can serve reads). Provides fault tolerance and automatic failover. ### 5. Sharded Cluster Horizontal scaling. Made up of: - *Shards*, sets of replicas each holding part of the data - *mongos*, the query routers - *Config servers*, holding metadata about how the data is distributed ### 6. Optional integrations - *Client drivers* (Node, Python, Go, and others), for applications to talk to the server - *Ops Manager / Atlas*, monitoring, management, automation - *Security components*, roles, authentication, TLS, auditing Altogether, MongoDB's architecture is a combination of `mongod` processes, `mongos` and config servers when needed, plus the storage and replication subsystems that provide scalability, fault tolerance, and availability.For the reviewerNote to the moderator (optional)Visible only to the moderator. Helps review go faster.