Forward Internal

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.

Configuration Reference

This is the 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

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 inbound 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).

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 for more information.

Managing Fallback Behavior (`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.

Examples

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

YAML
JSON

---
inbound:
  - actions:
      - type: "forward-internal"
        config:
          url: "https://example.private"

{
  "inbound": [
    {
      "actions": [
        {
          "type": "forward-internal",
          "config": {
            "url": "https://example.private"
          }
        }
      ]
    }
  ]
}

Start Private Endpoint

ngrok http 80 --url example.private --binding private

Start Public Endpoint with Traffic Policy

ngrok http 8080 --url forward-internal-example.ngrok.io --traffic-policy-file /path/to/policy.yml

Example Request

$ 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

Action Result Variables

The following variables are made available for use in subsequent expressions and CEL interpolations after the action has run. Variable values will only apply to the last action execution, results are not concatenated.

This action does not set any variables after it has been executed.

Overview​

Configuration Reference​

Action Type​

Configuration Fields​

Supported Directions​

Supported Schemes​

Behavior​

HTTP Headers​

Managing Fallback Behavior (on_error)​

Examples​

Basic Example​

Example Traffic Policy Document​

Start Private Endpoint​

Start Public Endpoint with Traffic Policy​

Example Request​

Action Result Variables​