1# Azure Cosmos DB
2 
3Globally distributed, multi-model database for low-latency data at scale.
4 
5## When to Use
6 
7- Global distribution requirements
8- Multi-model data (document, graph, key-value)
9- Variable and unpredictable throughput
10- Low-latency reads/writes at scale
11- Flexible schema requirements
12 
13## Required Supporting Resources
14 
15| Resource | Purpose |
16|----------|---------|
17| None required | Cosmos DB is fully managed |
18| Key Vault | Store connection strings (recommended) |
19 
20## Capacity Modes
21 
22| Mode | Use Case | Billing |
23|------|----------|---------|
24| **Serverless** | Variable/low traffic, dev/test | Per request |
25| **Provisioned** | Predictable workloads | Per RU/s |
26| **Autoscale** | Variable but predictable peaks | Per max RU/s |
27 
28## Consistency Levels
29 
30| Level | Latency | Consistency |
31|-------|---------|-------------|
32| Strong | Highest | Linearizable |
33| Bounded Staleness | High | Bounded |
34| Session | Medium | Session-scoped |
35| Consistent Prefix | Low | Prefix ordering |
36| Eventual | Lowest | Eventually consistent |
37 
38Recommendation: Use **Session** for most applications.
39 
40## Environment Variables
41 
42| Variable | Value |
43|----------|-------|
44| `COSMOS_CONNECTION_STRING` | Primary connection string (Key Vault reference) |
45| `COSMOS_ENDPOINT` | Account endpoint URL |
46| `COSMOS_DATABASE` | Database name |
47 
48## References
49 
50- [Bicep Patterns](bicep.md)
51- [Partition Key Selection](partitioning.md)
52- [SDK Connection Patterns](sdk.md)
53