FerretDB vs MongoDB Compatibility and License Risk — what do I need to change?
Pick a MongoDB-compatible database when API coverage, managed options, and licensing risk changed enough by 2026 that older comparisons are stale.
Blockers
- Lock-in via vendor/mongodb
- Lock-in via engine/postgresql
- Lock-in via engine/postgresql
- requires_version: package/ferretdb-cloud → runtime/mongodb-5
- requires_version: package/ferretdb → runtime/mongodb-5
- requires_version: package/ferretdb → protocol/mongodb-wire-protocol
Who this is for
- cost-sensitive
- low-ops
- enterprise
- compliance
Candidates
MongoDB Atlas
MongoDB Atlas is the reference managed MongoDB service and still has the lowest compatibility risk for teams that need the broadest MongoDB feature coverage. As of 2026-03-30, MongoDB lists Atlas Flex at "$0.011/hour" with "Up to $30/month," and Dedicated clusters starting at "$0.08/hour" and "$56.94/month." MongoDB also continues to offer self-managed Community Edition and Enterprise Advanced, while the Server Side Public License remains the governing public license for MongoDB server code. The key differentiator is maximum API and ecosystem compatibility with the tradeoff of the highest licensing and vendor-dependence surface.
When to choose
Use this when you need the fewest migration surprises, the fullest MongoDB feature surface, or managed operations with mainstream vendor support. It is the default choice for enterprise teams that cannot absorb compatibility gaps and can accept Atlas dependency or commercial licensing conversations.
Tradeoffs
Best compatibility and managed maturity, but the SSPL creates legal review overhead for service-provider and platform scenarios, and Atlas is the highest lock-in path.
Cautions
If your company may offer MongoDB functionality as a service, review SSPL section 13 carefully. Atlas entry pricing is now centered on Flex and Dedicated, so older advice that assumes previous low-end cluster options may be outdated.
FerretDB Cloud
FerretDB Cloud is a fully managed MongoDB-compatible service announced on 2025-08-25 and is built on PostgreSQL plus the open-source DocumentDB extension instead of MongoDB server. As of 2026-03-30, FerretDB documentation is at version "v2.7" and states that FerretDB works with MongoDB 5.0+ drivers while also stating it is not "100% compatible" with MongoDB. The launch announcement lists Free, Pro, Enterprise, and BYOA tiers, but public numeric pricing was not verifiable from official pages in this search pass, so check official docs for current prices. The key differentiator is managed deployment with Apache 2.0 licensing and a lower MongoDB license-risk profile.
When to choose
Use this when you want a managed service but MongoDB licensing and long-term portability are first-order concerns. It fits low-ops plus cost-sensitive or compliance-conscious teams that can tolerate some API gaps and will validate workload compatibility before committing.
Tradeoffs
Lower licensing risk and now a real managed option, but compatibility still trails MongoDB and public pricing is less transparent from the official sources reviewed.
Cautions
Do not treat FerretDB Cloud as a full MongoDB drop-in without pre-migration testing. FerretDB publishes supported and missing commands, and that list should drive the decision more than generic "MongoDB-compatible" marketing.
Self-managed FerretDB on PostgreSQL
Self-managed FerretDB is an Apache 2.0 licensed MongoDB-compatible proxy that, as of docs version "v2.7," converts MongoDB 5.0+ wire protocol queries to SQL and uses PostgreSQL with the DocumentDB extension as its database engine. FerretDB explicitly positions itself as free from MongoDB licensing restrictions, which materially changes the legal risk profile versus running SSPL MongoDB server code. Its compatibility documentation says MongoDB 5.0+ drivers should work, but it also lists notable gaps such as missing `bulkWrite`, missing transaction commands like `abortTransaction` and `commitTransaction`, and missing role-management commands. The key differentiator is license clarity and infrastructure control rather than perfect API coverage.
When to choose
Use this when you want MongoDB-style drivers and tooling but need open-source licensing and are already comfortable running PostgreSQL yourself. It is the strongest fit for cost-sensitive or compliance-sensitive teams that can own more operations and can gate adoption on workload-specific tests.
Tradeoffs
Apache 2.0 licensing and PostgreSQL leverage are strong advantages, but you inherit operational burden and must accept compatibility and performance differences versus native MongoDB.
Cautions
FerretDB says exact error messages may differ from MongoDB, collection names must be valid UTF-8, and production suitability must be verified per workload. If your application depends on transactions, role-management coverage, or unimplemented admin commands, treat that as a hard blocker until tested.
Try with your AI agent
$ npm install -g pocketlantern $ pocketlantern init # Restart Claude Code, Cursor, or your MCP client, then ask: # "FerretDB vs MongoDB Compatibility and License Risk — what do I need to change?"