Add netstack (#119)

* Add netstack

* Update page to add a use case

* updated the description

---------

Co-authored-by: Zoltan Papp <zoltan.papp@webkeyapp.com>
Co-authored-by: Maycon Santos <mlsmaycon@gmail.com>

src/components/NavigationDocs.jsx

@@ -57,6 +57,7 @@ export const docsNavigation = [
             { title: 'Monitor system and network activity', href: '/how-to/monitor-system-and-network-activity' },
             { title: 'Activity event streaming', href: '/how-to/activity-event-streaming' },
             { title: 'Access NetBird API', href: '/how-to/access-netbird-public-api' },
+            { title: 'Running NetBird on FaaS', href: '/how-to/netbird-on-faas' },
             { title: 'Examples', href: '/how-to/examples' },
             { title: 'CLI', href: '/how-to/cli' },
             { title: 'Delete your NetBird account', href: '/how-to/delete-account' },

src/pages/how-to/netbird-on-faas.mdx

@@ -0,0 +1,56 @@
+
+# Running NetBird on FaaS environments
+
+Function as a Service (FaaS) is a cloud computing model where developers deploy small, specific-purpose code functions, managed by a cloud provider. 
+FaaS environments, however, impose restrictions like limited access to the system's root, kernel, and network stack, crucial for security in shared cloud infrastructure.
+
+Since [v0.25.3](https://github.com/netbirdio/netbird/releases), NetBird enables secure connectivity and access from serverless functions like AWS lambda and Azure Functions to cloud or on-premises servers, 
+containers, databases, and other internal resources. NetBird has adapted to the constraints of FaaS environments by leveraging netstack from 
+the [gVisor](https://github.com/google/gvisor) Go package, which is part of [Wireguard-go](https://github.com/netbirdio/wireguard-go), 
+enabling the WireGuard stack to run entirely in userspace. This approach circumvents the typical need for network or kernel-level access.
+
+## How to enable netstack mode?
+You can enable the netstack mode for the NetBird client using environment variables:
+
+`NB_USE_NETSTACK_MODE`: Set to true to enable netstack mode. (Default: false)
+`NB_SOCKS5_LISTENER_PORT`: Set the port where the Socks5 proxy listens. (Default: 1080)
+
+With these variables, NetBird will launch a Socks5 proxy that you can use to connect to your internal resources.
+
+<Note>
+    The DNS feature is not supported. You can reach the peers by IP address only.
+</Note>
+
+### Running locally
+```bash
+export NB_USE_NETSTACK_MODE=true
+export NB_SOCKS5_LISTENER_PORT=30000
+netbird up -F
+```
+
+### Docker
+Some container environments can be restricted as well. For example, Docker containers are not allowed to create new VPN interfaces by default. For that reason, you can run a NetBird agent in a standard mode to enable the netstack mode:
+```bash
+docker run --rm --name PEER_NAME --hostname PEER_NAME -d \
+-e NB_SETUP_KEY=<SETUP KEY> -e NB_USE_NETSTACK_MODE=true -e  NB_SOCKS5_LISTENER_PORT=1080 -v netbird-client:/etc/netbird netbirdio/netbird:latest
+```
+This is useful when you want to configure a simple routing peer without adding privileged permissions or linux capabilities.
+
+## How to use the SOCKS5 proxy?
+Once you have the agent running in netstack mode, you need to configure your application to use the SOCKS5 proxy. The following is an example of a python 3 application:
+```python
+import socks
+import socket
+import os
+def Example():
+    socks.set_default_proxy(socks.SOCKS5, "127.0.0.1", int(os.getenv('NB_SOCKS5_LISTENER_PORT', '1080')))
+    socket.socket = socks.socksocket
+    # rest of the code...
+```
+## How to use NetBird in FaaS environments?
+Cloud providers like AWS and Azure, allow you to configure custom runtime environments for their function services, in AWS this is called Lambda Layers, 
+and in Azure, it's called containerized Azure Functions.
+
+There are many ways that you can configure these environments with NetBird's client binary. We have created a simple example using containerized Azure Functions, 
+which you can find [Azure functions python db access example
+](https://github.com/netbirdio/azure-functions-python-db-access).