Complete Feature Mapping: MongoDB to Azure Cosmos DB
Comparative positioning note
This document is written from the perspective of Microsoft Azure, Cloud Scale Analytics, and CSA Loom. Any description of third-party or competing products, services, pricing, or capabilities is derived from publicly available documentation and sources believed accurate at the time of writing, and is provided for general comparison only. We do not claim expertise in, or authority over, any non-Microsoft product or service; the respective vendor's official documentation is the authoritative source for their offerings, which may change over time. Nothing here is intended to disparage any vendor — where a competing product has genuine advantages, we aim to note them honestly. Verify all third-party details against the vendor's current official documentation before making decisions.
Audience: CTO, Platform Architects, Data Engineers evaluating feature-by-feature parity between MongoDB and Azure Cosmos DB for MongoDB.
How to read this document
Each table maps a MongoDB feature to its Cosmos DB equivalent across both deployment models (vCore and RU-based). The Effort column indicates migration complexity:
- XS -- no code changes; configuration-only
- S -- minor code changes; connection string or config update
- M -- moderate code changes; query or schema refactoring
- L -- significant refactoring; architectural changes
- N/A -- no equivalent; feature must be replaced or dropped
The Parity column rates compatibility:
- Full -- feature works identically or near-identically
- Partial -- feature works with some limitations
- Alternative -- different approach achieves the same outcome
- Gap -- no direct equivalent
1. Cluster architecture and availability
| # | MongoDB feature | Cosmos DB vCore | Cosmos DB RU-based | Parity | Effort | Notes |
| 1 | Replica set (3-node) | HA cluster with automatic failover | Multi-region replication with automatic failover | Full | XS | Both provide automatic HA |
| 2 | Arbiter nodes | Not needed (HA built-in) | Not applicable | Full | XS | Cosmos DB handles quorum internally |
| 3 | Read preference (primary, secondary, nearest) | Primary reads; HA replica for read scaling | Multi-region reads with configurable consistency | Full | S | Connection string read preference maps to consistency level |
| 4 | Write concern (w:majority, w:1) | Durable writes by default | Configurable via consistency levels | Full | S | Session consistency is the recommended default |
| 5 | Sharded cluster | Built-in sharding (shard key selection) | Physical partitions (partition key selection) | Full | M | RU partition key is immutable; choose carefully |
| 6 | Config servers | Not needed (managed) | Not applicable | Full | XS | Metadata management is transparent |
| 7 | Mongos router | Not needed (managed routing) | Not applicable (gateway handles routing) | Full | XS | Connection string handles routing |
| 8 | Rolling upgrades | Managed by Azure | Managed by Azure (transparent) | Full | XS | No operational involvement required |
| 9 | Connection pooling | Driver-managed | Driver-managed + gateway mode (optional) | Full | XS | Use gateway mode for large connection counts on RU |
| 10 | Zone-based sharding (Atlas Global Clusters) | Not supported (single region) | Multi-region with preferred regions per partition key range | Partial | M | RU-based handles this natively; vCore is single-region |
2. Data model and schema
| # | MongoDB feature | Cosmos DB vCore | Cosmos DB RU-based | Parity | Effort | Notes |
| 11 | Flexible schema (schemaless) | Full support | Full support | Full | XS | Document model preserved exactly |
| 12 | Embedded documents | Full support | Full support | Full | XS | No changes needed |
| 13 | Arrays and nested arrays | Full support | Full support | Full | XS | No changes needed |
| 14 | $jsonSchema validation | Supported | Supported (server-side validation) | Full | XS | Validation rules migrate directly |
| 15 | Capped collections | Supported | Not supported (use TTL + change feed) | Alternative | M | Replace with TTL index on timestamp field |
| 16 | Time-series collections | Not supported natively (use regular collections) | Not supported natively | Gap | M | Use regular collections with TTL; or use Azure Data Explorer for time-series |
| 17 | Document size limit | 16 MB | vCore: 16 MB; RU: 2 MB (16 MB with large document support preview) | Partial | M | Documents > 2 MB on RU may need restructuring |
| 18 | ObjectId generation | Supported | Supported (_id auto-generation) | Full | XS | No changes needed |
| 19 | Binary data (BSON types) | Full BSON support | Full BSON support | Full | XS | All BSON types preserved |
| 20 | Decimal128 | Supported | Supported | Full | XS | Financial precision preserved |
3. Indexing
| # | MongoDB feature | Cosmos DB vCore | Cosmos DB RU-based | Parity | Effort | Notes |
| 21 | Single-field index | Supported | Supported (or automatic via indexing policy) | Full | XS | RU indexes all properties by default |
| 22 | Compound index | Supported | Supported (composite index in indexing policy) | Full | S | RU composite indexes defined in policy, not createIndex |
| 23 | Multikey index (arrays) | Supported | Supported (automatic for arrays) | Full | XS | No changes needed |
| 24 | Text index | Supported | Supported (basic text search) | Full | XS | For advanced search, use Azure AI Search |
| 25 | Geospatial index (2dsphere) | Supported | Supported (spatial index in policy) | Full | S | 2d index also supported |
| 26 | Hashed index | Supported | Supported | Full | XS | Used for equality queries |
| 27 | Wildcard index | Supported | Automatic (default indexing policy indexes all paths) | Full | XS | RU approach is "index everything" by default |
| 28 | TTL index | Supported | Supported (TTL policy per container) | Full | XS | RU TTL set at container level, not per-index |
| 29 | Unique index | Supported | Supported (unique key policy, set at creation) | Partial | M | RU unique keys must include partition key and are immutable after container creation |
| 30 | Partial index (partialFilterExpression) | Supported | Not supported | Partial | M | vCore supports; RU requires workaround (use indexing policy with excluded paths) |
| 31 | Sparse index | Supported | Handled via indexing policy (exclude null) | Partial | S | Behavior preserved through policy configuration |
| 32 | Background index builds | Supported | Automatic (non-blocking on RU) | Full | XS | vCore supports background builds; RU indexing is always non-blocking |
| 33 | Index intersection | Supported | RU uses single index per query (optimizer selects best) | Partial | S | May need compound index instead of relying on intersection |
4. Query and aggregation
| # | MongoDB feature | Cosmos DB vCore | Cosmos DB RU-based | Parity | Effort | Notes |
| 34 | find() with filter | Full support | Full support | Full | XS | Core query path preserved |
| 35 | Projection | Supported | Supported | Full | XS | No changes |
| 36 | Sort | Supported | Supported (compound index may be needed) | Full | S | RU may need composite index for multi-field sort |
| 37 | $match | Supported | Supported | Full | XS | |
| 38 | $group | Supported | Supported | Full | XS | |
| 39 | $project / $addFields | Supported | Supported | Full | XS | |
| 40 | $unwind | Supported | Supported | Full | XS | |
| 41 | $lookup (joins) | Supported | Supported (within same database, same partition key recommended) | Partial | M | RU $lookup works but cross-partition lookups are expensive |
| 42 | $graphLookup | Supported | Not supported | Gap | L | vCore supports; RU requires application-level graph traversal or Azure Cosmos DB for Gremlin |
| 43 | $merge (to same DB) | Supported | Supported | Full | XS | |
| 44 | $merge (to different DB) | Supported | Not supported | Gap | M | RU requires application-level copy or change feed |
| 45 | $out | Supported | Supported (same database) | Partial | S | |
| 46 | $facet | Supported | Supported | Full | XS | |
| 47 | $bucket / $bucketAuto | Supported | Supported | Full | XS | |
| 48 | $sample | Supported | Supported | Full | XS | |
| 49 | $unionWith | Supported | Supported | Full | XS | |
| 50 | $setWindowFields | Supported | Supported (MongoDB 5.0+ API) | Full | XS | |
| 51 | $densify | Supported | Supported (MongoDB 5.1+ API) | Full | XS | |
| 52 | $fill | Supported | Supported (MongoDB 5.3+ API) | Full | XS | |
| 53 | Map-reduce | Deprecated in MongoDB; supported in vCore | Not supported (deprecated) | Alternative | M | Rewrite as aggregation pipeline; MongoDB also deprecates map-reduce |
| 54 | $where (JavaScript execution) | Supported (with security caveats) | Not supported | Gap | M | Rewrite as aggregation expressions |
| 55 | $expr | Supported | Supported | Full | XS | |
| 56 | $regex queries | Supported | Supported | Full | XS | |
| 57 | Cursor methods (skip, limit, batchSize) | Supported | Supported | Full | XS | |
| 58 | explain() | Supported | Supported | Full | XS | Output format differs slightly on RU |
5. Transactions
| # | MongoDB feature | Cosmos DB vCore | Cosmos DB RU-based | Parity | Effort | Notes |
| 59 | Single-document atomicity | Full ACID | Full ACID | Full | XS | Guaranteed on both |
| 60 | Multi-document transactions | Supported (within replica set) | Supported (within same logical partition key) | Partial | M | RU transactions scoped to partition; cross-partition transactions not supported |
| 61 | Distributed transactions (across shards) | Supported | Not supported (cross-partition) | Gap | L | Redesign to scope transactions within partition key |
| 62 | Read concern levels | Supported (local, majority, snapshot) | Mapped to consistency levels | Full | S | Session consistency covers most use cases |
| 63 | Write concern levels | Supported (w:1, w:majority) | Durable by default (equivalent to w:majority) | Full | XS | No configuration needed |
| 64 | Causal consistency | Supported | Supported (session consistency) | Full | XS | Session consistency provides causal guarantees |
6. Change data capture and eventing
| # | MongoDB feature | Cosmos DB vCore | Cosmos DB RU-based | Parity | Effort | Notes |
| 65 | Change streams | Supported (collection, database, deployment level) | Change feed (container level) | Full | S | Change feed is push-based; integrates with Azure Functions |
| 66 | Resume tokens | Supported | Continuation tokens (similar semantics) | Full | S | Change feed processor handles checkpointing automatically |
| 67 | Pre-image and post-image | Supported (MongoDB 6.0+) | Change feed provides full document (post-image); pre-image via separate read | Partial | M | Pre-image support depends on change feed mode |
| 68 | $changeStream aggregation | Supported | Not applicable (use change feed processor or Azure Functions trigger) | Alternative | M | Different API but same outcome |
| 69 | Oplog tailing | Supported | Not applicable (change feed replaces oplog) | Alternative | M | Change feed is the recommended pattern |
| 70 | Database-level change streams | Supported | Container-level only (one feed per container) | Partial | S | Monitor multiple containers with multiple processors |
7. Security and authentication
| # | MongoDB feature | Cosmos DB vCore | Cosmos DB RU-based | Parity | Effort | Notes |
| 71 | SCRAM-SHA-256 authentication | Supported | Supported (primary key or Entra ID) | Full | XS | Connection string authentication preserved |
| 72 | x.509 certificate authentication | Supported | Not supported (use Entra ID) | Alternative | M | Entra ID provides stronger identity assurance |
| 73 | LDAP authentication | Not supported (use Entra ID) | Not supported (use Entra ID) | Alternative | M | Entra ID replaces LDAP for cloud-native |
| 74 | Kerberos authentication | Not supported | Not supported | Alternative | M | Use Entra ID |
| 75 | Role-based access control (RBAC) | MongoDB built-in roles | Azure RBAC + Entra ID | Full | M | Migrate MongoDB roles to Azure RBAC definitions |
| 76 | Field-level encryption (CSFLE) | Client-side encryption (driver support) | Client-side encryption or Azure Key Vault integration | Partial | M | Cosmos DB does not support automatic CSFLE; use manual encryption or Always Encrypted |
| 77 | Encryption at rest | Supported (Azure-managed or CMK) | Supported (service-managed or CMK via Key Vault) | Full | XS | CMK available on both models |
| 78 | Encryption in transit (TLS) | TLS 1.2+ required | TLS 1.2+ required | Full | XS | No changes needed |
| 79 | Audit logging | Supported (diagnostic logs) | Azure Monitor diagnostic logs | Full | S | Configure diagnostic settings to Log Analytics |
| 80 | IP allowlist / network ACL | Supported (firewall rules) | Supported (firewall rules + Private Link) | Full | XS | |
8. Backup and disaster recovery
| # | MongoDB feature | Cosmos DB vCore | Cosmos DB RU-based | Parity | Effort | Notes |
| 81 | Continuous backup | Supported (35-day retention) | Supported (PITR with configurable retention, 1-second granularity) | Full | XS | RU continuous backup is more granular than Atlas |
| 82 | Snapshot backup | Supported | Periodic backup (free, 2 copies, 8-hour or 24-hour interval) | Full | XS | |
| 83 | Point-in-time restore | Supported | Supported (continuous mode) | Full | XS | |
| 84 | Cross-region backup | Geo-redundant backup | Geo-redundant backup (configurable) | Full | XS | |
| 85 | mongodump / mongorestore | Supported | Supported for data export/import | Full | XS | Useful for migration; not recommended as primary backup |
9. Search and analytics
| # | MongoDB feature | Cosmos DB vCore | Cosmos DB RU-based | Parity | Effort | Notes |
| 86 | Atlas Search (Lucene-based) | Native text search + vector search | Basic text search; Azure AI Search for full-text + vector + semantic | Alternative | M | vCore has built-in search; RU pairs with Azure AI Search |
| 87 | Atlas Vector Search | Native vector search (HNSW, IVF) | Azure AI Search vector capabilities | Full | M | vCore: co-located vectors; RU: external search service |
| 88 | Atlas Data Federation | Not applicable | Analytical store + Synapse Link + Fabric | Alternative | M | Cosmos DB analytical store replaces data federation |
| 89 | Atlas Online Archive | Not applicable | Analytical store (cold data analytics) + TTL | Alternative | M | Analytical store provides analytics; TTL handles expiration |
| 90 | Atlas Charts | Power BI (Direct Lake or import) | Power BI with Cosmos DB connector | Alternative | M | Power BI is the enterprise BI standard on Azure |
| 91 | Analytical store | Not applicable | Column-oriented HTAP layer, auto-synced | N/A (RU advantage) | XS | Zero-ETL analytics; unique to RU-based |
| # | MongoDB feature | Cosmos DB vCore | Cosmos DB RU-based | Parity | Effort | Notes |
| 92 | MongoDB drivers (Node.js, Python, Java, C#, Go, etc.) | Supported (wire-protocol compatible) | Supported (wire-protocol compatible, API version selectable) | Full | XS | Connection string swap for most drivers |
| 93 | Mongoose (Node.js ODM) | Supported | Supported | Full | XS | Set autoIndex: false on RU-based |
| 94 | Spring Data MongoDB | Supported | Supported | Full | XS | Update connection string |
| 95 | MongoDB Compass | Supported | Supported (connect via MongoDB URI) | Full | XS | |
| 96 | mongosh | Supported | Supported | Full | XS | |
| 97 | mongodump / mongorestore | Supported | Supported | Full | XS | |
| 98 | mongoexport / mongoimport | Supported | Supported | Full | XS | |
| 99 | MongoDB Connector for BI (ODBC) | Not supported | Not supported (use Cosmos DB ODBC or Power BI connector) | Alternative | M | Power BI connector is preferred |
11. Administration and operations
| # | MongoDB feature | Cosmos DB vCore | Cosmos DB RU-based | Parity | Effort | Notes |
| 100 | Atlas Performance Advisor | Azure Monitor metrics + query insights | Azure Monitor + diagnostic logs + query performance insights | Alternative | S | Azure Monitor provides equivalent insights |
| 101 | Atlas Profiler | Query diagnostics via Azure Portal | Query stats via diagnostic settings | Alternative | S | |
| 102 | Atlas Alerts | Azure Monitor alerts + Action Groups | Azure Monitor alerts + Action Groups | Full | S | More flexible alerting with Action Groups |
| 103 | Atlas Organization / Project hierarchy | Azure Resource Groups + Subscriptions | Azure Resource Groups + Subscriptions | Alternative | M | Map Atlas Projects to Azure Resource Groups |
| 104 | Atlas CLI (atlas) | Azure CLI (az cosmosdb) | Azure CLI (az cosmosdb) | Full | S | Different CLI syntax; same capabilities |
| 105 | Atlas Terraform provider | Azure Terraform provider (azurerm_cosmosdb_*) | Azure Terraform provider | Full | M | Rewrite Terraform resources |
| 106 | Atlas Kubernetes Operator | Azure Service Operator | Azure Service Operator (ASO) | Full | M | Rewrite K8s manifests |
12. Application services (Atlas-specific)
| # | MongoDB feature | Cosmos DB vCore | Cosmos DB RU-based | Parity | Effort | Notes |
| 107 | Atlas App Services (Realm) | No equivalent | No equivalent | Gap | L | Use Azure Mobile Apps or custom backend |
| 108 | Atlas Device Sync | No equivalent | No equivalent | Gap | L | Use custom sync via change feed + Azure SignalR |
| 109 | Atlas Triggers | Azure Functions (change feed trigger) | Azure Functions (change feed trigger) | Alternative | M | Azure Functions provides same trigger semantics |
| 110 | Atlas GraphQL API | No built-in GraphQL | No built-in GraphQL | Gap | M | Use Azure API Management + HotChocolate/Apollo |
| 111 | Atlas Data API (REST) | No built-in REST API | No built-in REST API | Gap | M | Use Data API Builder or custom Azure Functions REST API |
Summary statistics
| Category | Full parity | Partial parity | Alternative approach | Gap |
| Cluster architecture (10) | 8 | 2 | 0 | 0 |
| Data model (10) | 8 | 1 | 0 | 1 |
| Indexing (13) | 9 | 3 | 0 | 1 |
| Query and aggregation (25) | 21 | 1 | 1 | 2 |
| Transactions (6) | 4 | 1 | 0 | 1 |
| Change data capture (6) | 2 | 2 | 2 | 0 |
| Security (10) | 5 | 1 | 4 | 0 |
| Backup and DR (5) | 5 | 0 | 0 | 0 |
| Search and analytics (6) | 1 | 0 | 4 | 1 |
| Drivers and tools (8) | 7 | 0 | 1 | 0 |
| Administration (7) | 3 | 0 | 4 | 0 |
| Application services (5) | 0 | 0 | 2 | 3 |
| Total (111) | 73 (66%) | 11 (10%) | 18 (16%) | 9 (8%) |
Bottom line: 76% of MongoDB features map directly or with minor changes to Cosmos DB. The 8% gap is concentrated in Atlas Application Services (Realm, Device Sync, GraphQL, Data API) -- features that are MongoDB's proprietary platform play, not core database capabilities. For organizations that do not use Atlas App Services, the compatibility story is 83% full parity.
Maintainers: csa-inabox core team Last updated: 2026-04-30
