Code Migration Phase

Migrate AWS Lambda function code to Azure Functions.

Prerequisites

• Assessment report completed
• Azure Functions extension installed in VS Code
• Best practices loaded via mcp_azure_mcp_get_azure_bestpractices tool

Rules

• If runtime is Python or Node.js: do NOT create function.json files
• If runtime is .NET (in-process or isolated) or Java: do NOT hand-author function.json — bindings metadata is generated from attributes/annotations at build time
• Use extension bundle version [4.*, 5.0.0) in host.json
• Use latest programming model (v4 for JavaScript, v2 for Python)
• Always use bindings and triggers instead of SDKs — For blob read/write, use input.storageBlob() / output.storageBlob() with extraInputs/extraOutputs. For queues, use app.storageQueue() or app.serviceBusQueue(). Only use SDK when there is no equivalent binding (e.g., Azure AI, custom HTTP calls)
• Always use the latest supported language runtime — Consult supported languages and select the newest GA version. Do NOT default to an older LTS version when a newer version is available on Azure Functions.

Steps

1. Install Azure Functions Extension — Ensure VS Code extension is installed
2. Load Best Practices — Use mcp_azure_mcp_get_azure_bestpractices tool for code generation guidance
3. Create Project Structure — Set up the Azure Functions project inside the output directory (<workspace-root-basename>-azure/). Do NOT create files inside the original AWS directory
4. Migrate Functions — Convert each Lambda function to Azure Functions equivalent
5. Update Dependencies — Replace AWS SDKs with Azure SDKs in package.json / requirements.txt
6. Configure Bindings — Set up triggers and bindings inline (v4 JS / v2 Python)
7. Configure Environment — Map Lambda env vars to Azure Functions app settings
8. Add Error Handling — Ensure proper error handling in all functions

Key Configuration Files

host.json

{
  "version": "2.0",
  "extensionBundle": {
    "id": "Microsoft.Azure.Functions.ExtensionBundle",
    "version": "[4.*, 5.0.0)"
  },
  "extensions": {
    "queues": {
      "maxPollingInterval": "00:00:02",
      "visibilityTimeout": "00:00:30",
      "batchSize": 1,
      "maxDequeueCount": 5
    }
  },
  "logging": {
    "applicationInsights": {
      "samplingSettings": {
        "isEnabled": true,
        "excludedTypes": "Request"
      }
    }
  }
}

Critical Infrastructure Dependencies

Blob Trigger with EventGrid Source — Additional Requirements

When migrating S3 event triggers to Azure blob triggers with source: 'EventGrid', the following infrastructure must be configured at the IaC level (not code level). Failure to set these up results in silent trigger failures.

See lambda-to-functions.md for Bicep patterns.

UAMI Credential Pattern

When using User Assigned Managed Identity (UAMI), DefaultAzureCredential() without arguments tries System Assigned first and fails. Always pass the client ID:

const credential = new DefaultAzureCredential({
  managedIdentityClientId: process.env.AZURE_CLIENT_ID
});

Add AZURE_CLIENT_ID as an app setting in Bicep pointing to the UAMI client ID.

azd init Workaround for Non-Empty Directories

azd init --template <template> refuses to run in a non-empty directory. Use a temp-directory approach:

1. azd init --template <template> in an empty temp directory
2. Copy IaC files (infra/, azure.yaml, etc.) into the project root
3. Clean up the temp directory

package.json (JavaScript)

{
  "dependencies": {
    "@azure/functions": "^4.0.0",
    "@azure/identity": "<latest>"
  },
  "devDependencies": {
    "@azure/functions-core-tools": "^4",
    "jest": "<latest>"
  }
}

Runtime-Specific Trigger & Binding Patterns

Load the appropriate runtime reference for the target language:

Scenario-Specific Guidance

See lambda-to-functions.md for detailed trigger mapping, code patterns, and examples.

Handoff to azure-prepare

After code migration is complete:

1. Update migration-status.md — mark Code Migration as ✅ Complete
2. Invoke azure-prepare — pass the assessment report context so it can:

• Use the service mapping as requirements input (skips manual gather-requirements)
• Generate IaC (Bicep/Terraform) for the mapped Azure services
• Create azure.yaml and .azure/preparation-manifest.md
• Apply security hardening

1. azure-prepare will then chain to azure-validate → azure-deploy