The options at a glance
| Option | What it is | MongoDB API compatible? | License |
|---|---|---|---|
| MongrelDB | Embedded database engine in Rust: documents, SQL, transactions, hybrid retrieval indexes, encryption. | No; native SQL and native query APIs | MIT or Apache-2.0 |
| FerretDB | Open-source proxy converting MongoDB wire protocol queries to SQL on PostgreSQL with the DocumentDB extension. | Yes, MongoDB 5.0+ wire protocol | Apache-2.0 |
| MongoDB Community Edition | The real MongoDB server, self-hosted on your own infrastructure. | Yes, it is MongoDB | Server Side Public License |
| Amazon DocumentDB | AWS managed document database service. | MongoDB API compatibility | Proprietary managed service |
| Postgres JSONB | Document columns inside the Postgres you already run. | No | PostgreSQL license |
Atlas: the baseline
Atlas is the managed cloud service for MongoDB, and its strength is operational: provisioning, scaling, backups, and monitoring handled by the vendor. The reasons teams shop for alternatives are cost shape, data-residency or ownership requirements, the Server Side Public License on the server itself, and workloads where a remote managed cluster is simply the wrong architecture, such as embedded products and local-first applications.
MongrelDB: the embedded option
MongrelDB is not MongoDB-compatible and does not try to be. It is an embedded database engine written in Rust for products where the database belongs inside the application or a local daemon: documents and typed tables with SQL, MVCC transactions and WAL durability, and hybrid retrieval indexes, dense ANN, sparse, FM substring, bitmap equality, learned range, and MinHash dedup, resolving through one RowId space. Storage is encrypted with AES-256-GCM, and the engine is MIT or Apache-2.0 licensed.
This replaces the Atlas shape rather than imitating it. If your workload is a desktop app, an agent runtime, an IoT device, or a service that should own its storage boundary, embedding removes the cluster, the network hop, and the monthly bill in one move. We maintain a direct MongrelDB vs MongoDB Atlas comparison for the head-to-head view.
FerretDB: keep the drivers, change the engine
FerretDB is an Apache-2.0 open-source MongoDB alternative written in Go: a proxy that converts MongoDB 5.0 and later wire protocol queries to SQL, using PostgreSQL with the DocumentDB extension as the database engine. Your existing MongoDB drivers and tooling keep working while storage lands on Postgres you operate.
That is the right shape when driver compatibility is the requirement and database ownership is the goal. The tradeoff is that behavior is a compatibility layer over Postgres semantics, so evaluation should cover the specific queries and aggregation stages your application depends on.
MongoDB Community Edition: the real thing, self-hosted
Self-hosting MongoDB Community Edition keeps the genuine engine, drivers, and tooling while moving operations onto your own hardware. The license to understand is the Server Side Public License: it is not OSI-approved, and its terms are the historical reason the compatible-alternative ecosystem exists. For many internal workloads that is a non-issue; for some product and SaaS shapes it is the deciding factor.
Amazon DocumentDB: relocate the managed boundary
DocumentDB is AWS's managed document database service with MongoDB API compatibility. It answers "we want managed, but inside our AWS accounts" rather than "we want to own the database." If your organization already runs everything on AWS, it consolidates operations; if your goal is leaving managed services, it changes the vendor, not the shape.
Postgres JSONB: when documents are a feature, not a database
A honest number of Atlas workloads are relational data with a few flexible columns. Postgres JSONB covers that shape inside a database you may already operate, with ACID transactions, point-in-time recovery, and every Postgres operational tool. The moment you need genuine document-database behavior at scale, or retrieval signals beyond btree and gin indexes, you are shopping for a database again, but for mixed workloads this is the cheapest exit on the list.
How to choose
Stay with Atlas when
- managed operations are worth the bill;
- your data-residency and ownership requirements are already satisfied;
- the application depends on MongoDB-specific features you do not want to re-evaluate.
Move when
- driver compatibility plus owned storage: FerretDB;
- the real engine on your own servers: MongoDB Community Edition;
- managed inside AWS: DocumentDB;
- documents as a feature of an existing Postgres: JSONB;
- the database belongs inside the product, with hybrid retrieval and encryption: MongrelDB.
Evaluation checklist
- List the MongoDB-specific features you actually use: aggregation stages, change streams, transactions, time series collections.
- Decide whether compatibility means "drivers keep working" or "query semantics match exactly." Those are different tests.
- Model the ownership requirement: who holds the backups, the encryption keys, and the pager.
- Test your three heaviest queries against any compatibility layer before migrating anything.
- Ask whether the workload needs a server at all. Embedded engines remove the question for local and product workloads.
Sources
MongoDB Atlas alternatives FAQ
What is the best self-hosted MongoDB Atlas alternative?
If you need MongoDB API compatibility, FerretDB is the open-source option that translates the MongoDB wire protocol to SQL on PostgreSQL. If you need the document model but not the API, self-hosted MongoDB Community Edition keeps the real thing on your own infrastructure. If the workload is an embedded product or local-first app, MongrelDB moves the database inside your process.
Is MongrelDB a MongoDB Atlas alternative?
For embedded and local workloads, yes. MongrelDB is not MongoDB wire-protocol compatible; it is an embedded database engine in Rust with documents, SQL, transactions, hybrid retrieval indexes, and AES-256-GCM encryption. It replaces the Atlas shape when the database should live inside your application or daemon rather than in a managed cloud.
Is MongoDB still open source?
MongoDB's server is licensed under the Server Side Public License, which is not an OSI-approved open-source license. That license choice is the reason compatible projects like FerretDB exist. MongrelDB itself is MIT or Apache-2.0.
What is FerretDB and how does it compare?
FerretDB is an Apache-2.0 open-source MongoDB alternative: a proxy that converts MongoDB 5.0 and later wire protocol queries to SQL, using PostgreSQL with the DocumentDB extension as its database engine. It keeps MongoDB drivers and tools working while moving storage onto Postgres you operate.
When does Amazon DocumentDB make sense instead?
DocumentDB is AWS's managed document database service with MongoDB API compatibility. It makes sense when you want to stay inside AWS operations and accept a different managed service instead of Atlas. It does not remove the managed-service boundary; it relocates it.