1# Azure Functions
2 
3Serverless compute for event-driven workloads, APIs, and scheduled tasks.
4 
5> **⚠️ MANDATORY: Use Composition Algorithm**
6>
7> **NEVER synthesize Bicep or Terraform from scratch for Azure Functions.**
8>
9> You MUST follow the base + recipe composition workflow:
10> 1. Load [selection.md](templates/selection.md) — decision tree for choosing base template + recipe
11> 2. Follow [composition.md](templates/recipes/composition.md) — the algorithm for fetching and composing
12>
13> This ensures proven IaC patterns, correct RBAC, and Flex Consumption defaults.
14 
15## When to Use
16 
17- Event-driven workloads
18- Scheduled tasks (cron jobs)
19- HTTP APIs with variable traffic
20- Message/queue processing
21- Real-time file processing
22- MCP servers for AI agents
23- Real-time streaming and event processing
24- Orchestrations and workflows (Durable Functions)
25 
26## Service Type in azure.yaml
27 
28```yaml
29services:
30  my-function:
31    host: function
32    project: ./src/my-function
33```
34 
35## Required Supporting Resources
36 
37| Resource | Purpose |
38|----------|---------|
39| Storage Account | Function runtime state |
40| App Service Plan | Hosting (Consumption or Premium) |
41| Application Insights | Monitoring |
42 
43## Hosting Plans
44 
45**Use Flex Consumption for new deployments** (all AZD templates default to Flex).
46 
47| Plan | Use Case | Scaling | VNET | Slots |
48|------|----------|---------|------|-------|
49| **Flex Consumption** ⭐ | Default for new projects | Auto, pay-per-execution | ✅ | ❌ |
50| Consumption Windows (Y1) | Legacy/maintenance, Windows-only features | Auto, scale to zero | ❌ | ✅ 1 staging slot |
51| Consumption Linux (Y1) | Legacy/maintenance | Auto, scale to zero | ❌ | ❌ |
52| Premium (EP1-EP3) | No cold starts, longer execution, slots | Auto, min instances | ✅ | ✅ 20 slots |
53| Dedicated | Predictable load, existing App Service | Manual or auto | ✅ | ✅ varies by SKU |
54 
55> ⚠️ **Deployment Slots Guidance:**
56> - **Windows Consumption (Y1)** supports 1 staging slot — valid for existing apps or specific Windows requirements.
57>   Prefer **Elastic Premium (EP1)** or **Dedicated** for new apps requiring slots, as Consumption cold starts affect swap reliability.
58> - **Linux Consumption and Flex Consumption** do **not** support deployment slots.
59> - For new projects needing slots: use **Elastic Premium** or an **App Service Plan (Standard+)**.
60 
61## Runtime Stacks
62 
63> **⚠️ ALWAYS QUERY OFFICIAL DOCUMENTATION FOR VERSIONS**
64>
65> Do NOT use hardcoded versions. Query for latest GA versions before generating code:
66>
67> **Primary Source:** [Azure Functions Supported Languages](https://learn.microsoft.com/en-us/azure/azure-functions/supported-languages)
68>
69> Use the azure-documentation MCP tool to fetch current supported versions:
70> ```yaml
71> intent: "Azure Functions supported language runtime versions"
72> learn: true
73> ```
74 
75### Version Selection Priority
761. **Latest GA** — For new projects (best features, longest support window)
772. **LTS** — For enterprise/compliance requirements
783. **User-specified** — When explicitly requested
79 
80| Language | FUNCTIONS_WORKER_RUNTIME | linuxFxVersion |
81|----------|-------------------------|----------------|
82| Node.js | `node` | `Node\|<version>` |
83| Python | `python` | `Python\|<version>` |
84| .NET | `dotnet-isolated` | `DOTNET-ISOLATED\|<version>` |
85| Java | `java` | `Java\|<version>` |
86| PowerShell | `powershell` | `PowerShell\|<version>` |
87 
88## References
89 
90- **[Selection Guide](templates/selection.md)** — Start here: decision tree for base + recipe
91- **[Composition Algorithm](templates/recipes/composition.md)** — How to fetch and compose templates
92- [AZD Templates](templates/README.md) — Template overview
93- [Bicep Patterns](bicep.md)
94- [Terraform Patterns](terraform.md)
95- [Durable Functions](durable.md)
96- [Aspire + Container Apps](aspire-containerapps.md)
97