# MongoDB on AWS — Atlas vs EC2 vs DocumentDB (July 2026)

| Option | Use when | Watch outs |
| --- | --- | --- |
| **MongoDB Atlas on AWS** | No dedicated DBA; want PITR, patching, UI ops | Tier list prices change — re-quote; sharding doubles floor cost |
| **Self-managed on EC2** | Dedicated DB ops + large clusters where Atlas premium > ops | You own failover drills, backups, upgrades |
| **Amazon DocumentDB** | Want AWS-managed API-compatible document store | **Not** full MongoDB — verify API/version (incl. 8.0 compat where offered) against your driver features |

## Cost levers (any path)

1. Drop unused indexes (WiredTiger cache pressure)  
2. Shard only after write/RAM bottleneck measured  
3. Avoid monotonic shard keys (hot shard)  
4. Size oplog for catch-up window  

## Quote before decide

Fill Atlas M-tier vs `r7g`×3 + EBS + backup + eng hours — never compare list compute alone.