How to access Aiven services from Google Cloud Functions via VPC peering

_toc.yml

@@ -180,6 +180,7 @@ entries:
     - file: docs/platform/howto/attach-vpc-aws-tgw
     - file: docs/platform/howto/manage-vpc-peering
     - file: docs/platform/howto/vpc-peering-gcp
+    - file: docs/platform/howto/google-cloud-functions
     - file: docs/platform/howto/vpc-peering-aws
     - file: docs/platform/howto/vnet-peering-azure
     - file: docs/platform/howto/vpc-peering-upcloud

docs/platform/howto/google-cloud-functions.rst

@@ -0,0 +1,103 @@
+How to access Aiven services from Google Cloud Functions via VPC peering
+========================================================================
+
+Once you have created a :doc:`VPC on the Aiven platform <manage-vpc-peering>` and :doc:`set up VPC peering on GCP <vpc-peering-gcp>`, you can follow these instructions to create **Serverless VPC access connector** and **Google Cloud Function**.
+
+By default, **Google Cloud Functions** can only access Internet and is not able to access your GCP VPC or Aiven VPC. For **Google Cloud Functions** to access VPC, **Serverless VPC access connector** is required. Under the hood, **serverless VPC access connector** consists of two or more Google-managed VM that forward requests (and perform NAT) from Cloud Functions to your GCP VPC and Aiven VPC.
+
+.. mermaid::
+
+    graph LR;
+
+        GCF(Google Cloud Function) --TCP session--> Conn(Serverless VPC access connector) --TCP session--> VPC(Your GCP VPC and Aiven VPC)
+
+First, create **Serverless VPC access connector**
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+
+1. Open GCP console and under **Navigation menu**, **Networking** section, **VPC network** product, select `Serverless VPC access <https://console.cloud.google.com/networking/connectors/list>`_
+2. Click **create connector**.
+
+   * **Name**: the connector name of your choice, 25 characters maximum
+   * **Region**: must be the region that you are intended to create Cloud Function
+   * **Network**: your GCP VPC, which should be peered to Aiven VPC already
+   * **Subnet**: select "custom IP range" and enter a /28 private subnet that is not in use.
+
+3. If you have **allowed IP addresses** configured on your Aiven service, please ensure the subnet of **serverless VPC access connector** is listed there
+
+Create **Cloud Function**
+~~~~~~~~~~~~~~~~~~~~~~~~~
+
+1. Open GCP console and under **Navigation menu**, **Serverless** section, select `Cloud Functions <https://console.cloud.google.com/functions/list>`_
+2. Click **create function**
+
+   * **Environment**: your choice, or leave it to the default (2nd gen)
+   * **Function name**: the name of your choice, 63 characters maximum
+   * **Region**: must be the region that you have the **serverless VPC access connector** created
+   * Click and expand the **runtime, build connections and security settings** section, select **Connections** tab, and select the **serverless VPC access connector** you have created.
+   * Click **Next**
+
+3. Select the runtime you prefer.
+
+   * **Pitfall**: if you click **test function** here, you will *not* able to access VPC.
+   * Click **Deploy**
+
+4. Wait for GCP to deploy the cloud function. Once deployed, use **source** tab to edit the function if needed. 
+
+   * **Pitfall**: if you click **test function** under **source** tab, you will *not* able to access VPC.
+
+5. Select **testing** tab and running test command in Cloud Shell *can* access VPC.
+
+
+Troubleshooting
+~~~~~~~~~~~~~~~
+
+If you cannot access your VPC or Aiven VPC from the Cloud Function, please consider using the following example for troubleshooting purposes.
+
+.. code-block:: python
+
+   # Cound Function 2nd gen, Python 3.11
+   import functions_framework
+   import socket
+
+   CLOUD_FUNCTION_KEY = 'gcf-aiven-test-CHANGE_ME_FOR_SECURITY_REASON'
+   
+   @functions_framework.http
+   def hello_http(request):
+       request_json = request.get_json(silent=True)
+   
+       if request_json and "cloud_function_key" in request_json and request_json["cloud_function_key"] == CLOUD_FUNCTION_KEY:
+           result = ""
+           try:
+               host = request_json['host']
+               port = request_json['port']
+               timeout = request_json.get('timeout', 10)
+               s = socket.socket(socket.AF_INET, socket.SOCK_STREAM)
+               s.settimeout(timeout)
+               s.connect((host, port))
+               result = "OK"
+           except Exception as e:
+               result = repr(e)
+               pass
+           return 'Result: {}\n'.format(result)
+       return "HTTP 401\n", 401
+
+The request body should contain
+
+* **CLOUD_FUNCTION_KEY**: Change this to protect your Cloud Function endpoint, especially if it does not require authentication.
+* **"host"**: FQDN or IP address if your Aiven service or VM in your GCP VPC.
+* **"port"**: Destination TCP port number.
+
+for example (e.g. in the **testing** tab in your **Cloud Function**)
+
+.. code-block:: json
+
+   {
+     "cloud_function_key": "gcf-aiven-test-CHANGE_ME_FOR_SECURITY_REASON",
+     "host": "fqdn-or-ip-to-your-aiven-service.a.aivencloud.com",
+     "port": 12345
+   }
+
+It will return "OK" if it can establish TCP 3-way handshaking. "TimeoutError" if it cannot reach the port specified.
+
+If you need help, please contact Aiven support. You can also provide your Cloud Function endpoint and CLOUD_FUNCTION_KEY so it would be more efficient for us to troubleshoot for you.
+