fix: API Endpoint Backend C_Migration

docs/DeploymentGuide.md

@@ -191,6 +191,8 @@ Review the configuration options below. You can customize any settings that meet
 | **Framework**          | Basic configuration               | [Well-Architected Framework](https://learn.microsoft.com/en-us/azure/well-architected/) |
 | **Features**           | Core functionality                | Reliability, security, operational excellence                                           |
 
+When you use the production WAF configuration for Container Migration, only the frontend Container App stays publicly reachable through Application Gateway/WAF. The backend API and processor Container Apps stay on internal ingress inside the Container Apps environment, and the existing VNet subnet/NSG rules continue to limit traffic to internal paths.
+
 **To use production configuration:**
 
 Copy the contents from the production configuration file to your main parameters file:

infra/main.bicep

@@ -1220,7 +1220,7 @@ module containerAppBackend 'br/public:avm/res/app/container-app:0.18.1' = {
       }
     ]
     ingressTargetPort: backendContainerPort
-    ingressExternal: true
+    ingressExternal: enablePrivateNetworking ? false : true // WAF: internal-only ingress for backend API
     scaleSettings: {
       maxReplicas: enableScalability ? 3 : 1
       minReplicas: 1
@@ -1278,7 +1278,14 @@ module containerAppFrontend 'br/public:avm/res/app/container-app:0.18.1' = {
         env: [
           {
             name: 'API_URL'
-            value: 'https://${containerAppBackend.outputs.fqdn}'
+            // Frontend calls same-origin /api; frontend server proxies to backend.
+            value: '/api'
+          }
+          {
+            name: 'BACKEND_API_URL'
+            value: enablePrivateNetworking
+              ? 'https://${backendContainerAppName}.internal.${containerAppsEnvironment.outputs.defaultDomain}'
+              : 'https://${containerAppBackend.outputs.fqdn}'
           }
           {
             name: 'APP_ENV'

infra/main_custom.bicep

@@ -1165,7 +1165,7 @@ module containerAppBackend 'br/public:avm/res/app/container-app:0.18.1' = {
       }
     ]
     ingressTargetPort: backendContainerPort
-    ingressExternal: true
+    ingressExternal: enablePrivateNetworking ? false : true
     scaleSettings: {
       maxReplicas: enableScalability ? 3 : 1
       minReplicas: 1
@@ -1229,7 +1229,13 @@ module containerAppFrontend 'br/public:avm/res/app/container-app:0.18.1' = {
         env: [
           {
             name: 'API_URL'
-            value: 'https://${containerAppBackend.outputs.fqdn}'
+            value: '/api'
+          }
+          {
+            name: 'BACKEND_API_URL'
+            value: enablePrivateNetworking
+              ? 'https://${backendContainerAppName}.internal.${containerAppsEnvironment.outputs.defaultDomain}'
+              : 'https://${containerAppBackend.outputs.fqdn}'
           }
           {
             name: 'APP_ENV'
@@ -1382,7 +1388,9 @@ output AZURE_CONTAINER_REGISTRY_ENDPOINT string = containerRegistry.outputs.logi
 output SERVICE_BACKEND_NAME string = containerAppBackend.outputs.name
 
 @description('Backend service container app URI')
-output SERVICE_BACKEND_URI string = 'https://${containerAppBackend.outputs.fqdn}'
+output SERVICE_BACKEND_URI string = enablePrivateNetworking
+  ? 'https://${backendContainerAppName}.internal.${containerAppsEnvironment.outputs.defaultDomain}'
+  : 'https://${containerAppBackend.outputs.fqdn}'
 
 @description('Processor service container app name')  
 output SERVICE_PROCESSOR_NAME string = containerAppProcessor.outputs.name

src/frontend/frontend_server.py

@@ -1,17 +1,20 @@
 import os
 
+import httpx
 import uvicorn
 from dotenv import load_dotenv
 from fastapi import FastAPI, Request
 from fastapi.middleware.cors import CORSMiddleware
-from fastapi.responses import FileResponse, HTMLResponse, JSONResponse
+from fastapi.responses import FileResponse, JSONResponse, Response
 from fastapi.staticfiles import StaticFiles
 
 # Load environment variables from .env file
 load_dotenv()
 
 app = FastAPI()
 
+BACKEND_API_URL = os.getenv("BACKEND_API_URL", "").rstrip("/")
+
 # Read allowed origins from environment; fall back to same-origin only
 _allowed_origins = os.getenv("ALLOWED_ORIGINS", "").split(",")
 _allowed_origins = [o.strip() for o in _allowed_origins if o.strip()]
@@ -72,6 +75,60 @@ async def get_config(request: Request):
     return config
 
 
+@app.api_route("/api/{full_path:path}", methods=["GET", "POST", "PUT", "PATCH", "DELETE", "OPTIONS"])
+async def proxy_api(full_path: str, request: Request):
+    if not BACKEND_API_URL:
+        return JSONResponse(status_code=503, content={"detail": "Backend API URL is not configured"})
+
+    target_url = f"{BACKEND_API_URL}/api/{full_path}"
+    if request.url.query:
+        target_url = f"{target_url}?{request.url.query}"
+
+    headers = dict(request.headers)
+    headers.pop("host", None)
+    headers.pop("content-length", None)
+
+    body = await request.body()
+
+    try:
+        async with httpx.AsyncClient(timeout=120.0, follow_redirects=True) as client:
+            proxied = await client.request(
+                method=request.method,
+                url=target_url,
+                headers=headers,
+                content=body,
+            )
+    except httpx.TimeoutException:
+        return JSONResponse(
+            status_code=504,
+            content={"detail": "Upstream backend request timed out"},
+        )
+    except httpx.RequestError:
+        return JSONResponse(
+            status_code=502,
+            content={"detail": "Failed to reach upstream backend"},
+        )
+
+    excluded_headers = {
+        "content-encoding",
+        "transfer-encoding",
+        "connection",
+        "content-length",
+        "content-type",
+    }
+
+    response = Response(
+        content=proxied.content,
+        status_code=proxied.status_code,
+        media_type=proxied.headers.get("content-type"),
+    )
+    for key, value in proxied.headers.multi_items():
+        if key.lower() not in excluded_headers:
+            response.raw_headers.append((key.encode("latin-1"), value.encode("latin-1")))
+
+    return response
+
+
 @app.get("/{full_path:path}")
 async def serve_app(full_path: str):
     # Resolve the requested path and ensure it stays within BUILD_DIR

src/frontend/requirements.txt

@@ -1,6 +1,7 @@
 fastapi==0.116.1
 uvicorn[standard]==0.35.0
 # uvicorn removed and added above to allow websocket support
+httpx==0.28.1
 jinja2==3.1.6
 azure-identity==1.24.0
 python-dotenv==1.1.1