Writing an Azure Function that serves all traffic to a subdomain

azure/all-traffic-to-subdomain.md

@@ -0,0 +1,42 @@
+# Writing an Azure Function that serves all traffic to a subdomain
+
+[Azure Functions](https://docs.microsoft.com/en-us/azure/azure-functions/) default to serving traffic from a path like `/api/FunctionName` - for example `https://your-subdomain.azurewebsites.net/api/MyFunction`.
+
+If you want to serve an entire website through a single function (e.g. using [Datasette](https://datasette.io/)) you need that function to we called for any traffic to that subdomain.
+
+Here's how to do that - to capture all traffic to any path under `https://your-subdomain.azurewebsites.net/`.
+
+First add the following section to your `host.json` file:
+
+```
+    "extensions": {
+        "http": {
+            "routePrefix": ""
+        }
+    }
+```
+Then add `"route": "{*route}"` to the `function.json` file for the function that you would like to serve all traffic. Mine ended up looking like this:
+```json
+{
+    "scriptFile": "__init__.py",
+    "bindings": [
+        {
+            "authLevel": "Anonymous",
+            "type": "httpTrigger",
+            "direction": "in",
+            "name": "req",
+            "route": "{*route}",
+            "methods": [
+                "get",
+                "post"
+            ]
+        },
+        {
+            "type": "http",
+            "direction": "out",
+            "name": "$return"
+        }
+    ]
+}
+```
+See https://github.com/simonw/azure-functions-datasette for an example that uses this pattern.