Initial docs for the Forward Internal action (#936)

Co-authored-by: Niji <[email protected]>
Co-authored-by: ℕ <[email protected]>

docs/http/index.mdx

@@ -585,7 +585,9 @@ ngrok is a compliant HTTP reverse proxy.
 
 ngrok adds headers to each HTTP request with information about the client IP
 and original protocol. These headers can be removed with the
-[Request Headers module](/http/request-headers#automatic-headers).
+[Request Headers module](/http/request-headers#automatic-headers) for Edges or
+the [Remove Headers action](/http/traffic-policy/actions/remove-headers/) for a
+Traffic Policy.
 
 | Header            | Description                                                                                   |
 | ----------------- | --------------------------------------------------------------------------------------------- |

docs/http/traffic-policy/actions/forward-internal.mdx

@@ -0,0 +1,18 @@
+import ActionBehavior from "/traffic-policy/actions/forward-internal/behavior.mdx";
+import ActionConfig from "/traffic-policy/actions/forward-internal/config.mdx";
+import ActionExamples from "/traffic-policy/actions/forward-internal/examples/index.mdx";
+import ActionOverview from "/traffic-policy/actions/forward-internal/index.mdx";
+import ActionVariables from "/traffic-policy/actions/forward-internal/variables.mdx";
+import ActionVariablesDescription from "/traffic-policy/common/action-variables-description.mdx";
+
+# Forward Internal
+
+<ActionOverview />
+<ActionConfig />
+<ActionBehavior />
+<ActionExamples />
+
+## Action Result Variables
+
+<ActionVariablesDescription />
+<ActionVariables />

docs/http/traffic-policy/actions/index.mdx

@@ -15,6 +15,7 @@ Traffic Policy actions enable you to modify the behavior of traffic flowing thro
 | [compress-response](compress-response) | Compress HTTP response bodies from your upstream server.              | Inbound, Outbound |
 | [custom-response](custom-response)     | Send a predefined custom response directly to the client.             | Inbound, Outbound |
 | [deny](deny)                           | Block incoming traffic to an endpoint.                                | Inbound           |
+| [forward-internal](forward-internal)   | Forward traffic to an endpoint within the same ngrok account.         | Inbound           |
 | [jwt-validation](jwt-validation)       | Validate JSON Web Tokens (JWT).                                       | Inbound           |
 | [log](log)                             | Add metadata to events for logging and monitoring.                    | Inbound, Outbound |
 | [rate-limit](rate-limit)               | Rate limit traffic to your upstream servers.                          | Inbound           |

traffic-policy/actions/forward-internal/behavior.mdx

@@ -0,0 +1,23 @@
+## Behavior
+
+When the Forward Internal action executes, it will look up the specified endpoint and relay any incoming traffic. The endpoint being forwarded to will behave as if the traffic was sent directly to it and execute all of the actions in its associated Traffic Policy. The endpoint being forwarded to must exist in the same ngrok account and be the same protocol as the forwarding endpoint (e.g. an HTTP public endpoint can only forward to an HTTP private endpoint). You also may not forward traffic to a second private endpoint or back to the original endpoint in a loop.
+
+If the forwarding is successful, the response from the upstream for the private endpoint will be sent back to the client making the original request. No further actions in the `on_http_request` phase will be executed and no traffic will be sent to the upstream for the public endpoint.
+
+If the forwarding is unsuccessful because the specified endpoint doesn't exist, is offline, or encounters another error, the action will return an error and follow the behavior that is specified by `on_error` (see [Managing Fallback Behavior](#on-error)).
+
+:::note
+Even if you do not plan to send traffic to a local service when creating a forwarding endpoint, you will still need to specify a local port. This port will receive traffic if an expression causes only a subset of traffic to be forwarded or if there is an error forwarding traffic and `on_error` is set to `continue` without a subsequent terminating action.
+:::
+
+### HTTP Headers
+
+When forwarding HTTP requests to another endpoint, the `Host` header will be set to the hostname of the forwarding endpoint. For example, if `example.ngrok.io` is forwarding HTTP requests to `example.private`, the `Host` header received by the upstream will be `example.ngrok.io`.
+
+The action will also set the `X-Forwarded-For`, `X-Forwarded-Host`, and `X-Forwarded-Proto` headers when making the upstream request. See [Upstream Headers](/docs/http#upstream-headers) for more information.
+
+### Managing Fallback Behavior (`on_error`) {#on-error}
+
+If `on_error` is set to `halt` (default) and the action encounters an error when forwarding traffic, the Traffic Policy chain will halt and no further actions will be executed. For example, if you have a `log` action after the `forward-internal` action and the `url` specified isn't an online endpoint, the `log` action will not be run and the error will be returned.
+
+However, if `on_error` is set to `continue`, actions that appear after the `forward-internal` action will still be executed even if the `forward-internal` action encounters an error. This can be used as a fallback to forward traffic to one of many endpoints depending which are online.

traffic-policy/actions/forward-internal/config.mdx

@@ -0,0 +1,27 @@
+## Configuration Reference
+
+This is the [Traffic Policy](/docs/http/traffic-policy/) configuration
+reference for this action.
+
+### Action Type
+
+`forward-internal`
+
+### Configuration Fields
+
+| Parameter  | Type     | Description                                                                                                                          |
+| ---------- | -------- | ------------------------------------------------------------------------------------------------------------------------------------ |
+| `url`      | `string` | **Required.** URL of the Endpoint to forward traffic to.                                                                             |
+| `binding`  | `string` | Binding of the Endpoint (only `private` is currently supported).                                                                     |
+| `on_error` | `string` | Whether or not further actions in the Traffic Policy should run if there is an error. Must be either `halt` (default) or `continue`. |
+
+### Supported Directions
+
+- `inbound`
+
+### Supported Schemes
+
+- `https`
+- `http`
+- `tls`
+- `tcp`

traffic-policy/actions/forward-internal/examples/basic-example.mdx

@@ -0,0 +1,65 @@
+import ConfigExample from "/src/components/ConfigExample.tsx";
+
+### Basic Example
+
+This example configuration will set up a public endpoint (`forward-internal-example.ngrok.io`) forwarding all traffic it receives to a private endpoint (`example.private`) that forwards the request to port `80` on your local machine. Since it is forwarding all traffic to the private endpoint, no traffic will be sent to `8080` which is the upstream port for the public endpoint.
+
+#### Example Traffic Policy Document
+
+<ConfigExample
+	snippetText={null}
+	showLineNumbers={true}
+	jsonMetastring="{5-51}"
+	yamlMetastring="{4-28}"
+	config={{
+		inbound: [
+			{
+				actions: [
+					{
+						type: "forward-internal",
+						config: {
+							url: "https://example.private",
+						},
+					},
+				],
+			},
+		],
+	}}
+/>
+
+#### Start Private Endpoint
+
+```shell
+ngrok http 80 --url example.private --binding private
+```
+
+#### Start Public Endpoint with Traffic Policy
+
+```shell
+ngrok http 8080 --url forward-internal-example.ngrok.io --traffic-policy-file /path/to/policy.yml
+```
+
+### Example Request
+
+```shell
+$ curl https://forward-internal-example.ngrok.io -v
+ ...
+> GET / HTTP/2
+> Host: forward-internal-example.ngrok.io
+> User-Agent: curl/[version]
+> Accept: */*
+...
+```
+
+This request will be forwarded to the private endpoint `https://example.private` which will then forward the request to port `80` on your local machine.
+
+```
+GET / HTTP/1.1
+Host: forward-internal-example.ngrok.io
+User-Agent: curl/[version]
+Accept: */*
+X-Forwarded-For: [ngrok IP]
+X-Forwarded-Host: forward-internal-example.ngrok.io
+X-Forwarded-Proto: https
+Accept-Encoding: gzip
+```

traffic-policy/actions/forward-internal/examples/index.mdx

@@ -0,0 +1,5 @@
+import BasicExample from "./basic-example.mdx";
+
+## Examples
+
+<BasicExample />

traffic-policy/actions/forward-internal/index.mdx

@@ -0,0 +1,3 @@
+## Overview
+
+The **Forward Internal** Traffic Policy action enables you to forward traffic from an endpoint to a private endpoint within the same ngrok account. This is useful for safely and securely routing traffic from your public endpoints to other services, giving you the ability to choose when and how your endpoints are made publicly available.

traffic-policy/actions/forward-internal/variables.mdx

@@ -0,0 +1 @@
+This action does not set any variables after it has been executed.