Traffic Policy

Overview

This module allows you to assign a policy to your endpoints containing a series of inbound and outbound rules that can be used to influence and control traffic to and from your upstream service.

Policy rules are composed of expressions that filter the traffic on which they are applicable and actions that should take effect.

Example Usage

Agent CLI

ngrok http 80 --policy-file /path/to/policy.yml

policy.yml

inbound:
  - name: FooBarParamNotFound
    expressions:
      - "'bar' in getQueryParam('foo')"
    actions:
      - type: "custom-response"
        config:
          status_code: 404
          content: not found
          headers:
            content-type: text/plain
  - name: "BazCookieForLargeRequests"
    expressions:
      - "!hasReqCookie('baz')"
      - "req.ContentLength > 5000"
    actions:
      - type: deny
outbound:
  - name: "LogUnsuccessfulRequests"
    expressions:
      - "res.StatusCode < '200' && res.StatusCode >= '300'"
    actions:
      - type: log
        config:
          metadata:
            hostport: example.com:443
            success: false

Agent Config

tunnels:
  example:
    proto: http
    addr: 80
    policy:
      inbound:
        - name: FooBarParamNotFound
          expressions:
            - "'bar' in getQueryParam('foo')"
          actions:
            - type: "custom-response"
              config:
                status_code: 404
                content: not found
                headers:
                  content-type: text/plain
        - name: "BazCookieForLargeRequests"
          expressions:
            - "!hasReqCookie('baz')"
            - "req.ContentLength > 5000"
          actions:
            - type: deny
      outbound:
        - name: "LogUnsuccessfulRequests"
          expressions:
            - "res.StatusCode < '200' && res.StatusCode >= '300'"
          actions:
            - type: log
              config:
                metadata:
                  hostport: example.com:443
                  success: false

SSH

info

Traffic Policy is not configurable via SSH

Go

import (
  "context"
  "net"

  "golang.ngrok.com/ngrok"
  "golang.ngrok.com/ngrok/config"
  "golang.ngrok.com/ngrok/policy"
)

func ngrokListener(ctx context.Context) (net.Listener, error) {
  return ngrok.Listen(ctx,
    config.HTTPEndpoint(
      config.WithPolicy(
        policy.Policy{
          Inbound: []policy.Rule{
            {
              Name: "FooBarParamNotFound",
              Expressions: []string{"'bar' in getQueryParam('foo')"},
              Actions: []policy.Action{
                {
                  Type: "custom-response",
                  Config: map[string]any{
                    "status_code": 400,
                    "content": "not found",
                    "headers": {
                      "content-type": "text/plain"
                    }
                  },
                },
              },
            },
            {
              Name: "BazCookieForLargeRequests",
              Expressions: []string{
                "!hasReqCookie('baz')",
                "req.ContentLength > 5000",
              },
              Actions: []policy.Action{
                {
                  Type: "deny",
                },
              },
            },
          },
          Outbound: []policy.Rule{
             {
              Name: "LogUnsuccessfulRequests",
              Expressions: []string{"res.StatusCode < '200' && res.StatusCode >= '300'"},
              Actions: []policy.Action{
                {
                  Type: "log",
                  Config: map[string]any{
                    "metadata": map[string]any{
                      "hostport": "example.com:443",
                      "success": false,
                    },
                  },
                },
              },
            },
          },
        },
      ),
    ),
    ngrok.WithAuthtokenFromEnv(),
  )
}

Go Package Docs:

• https://pkg.go.dev/golang.ngrok.com/ngrok/config#WithPolicy

Javascript

const ngrok = require("@ngrok/ngrok");
const fs = require("fs");

(async function () {
	const listener = await ngrok.forward({
		addr: 8080,
		authtoken_from_env: true,
		policy: fs.readFileSync("/path/to/policy.json", "utf8"),
	});

	console.log(`Ingress established at: ${listener.url()}`);
})();

policy.json

{
  "inbound":
    [
      {
        "name": "FooBarParamNotFound",
        "expressions": ["'bar' in getQueryParam('foo')"],
        "actions":
          [
            {
              "type": "custom-response",
              "config":
                {
                  "status_code": 404,
                  "content": "not found",
                  "headers": { "content-type": "text/plain" },
                },
            },
          ],
      },
      {
        "name": "BazCookieForLargeRequests",
        "expressions": ["!hasReqCookie('baz')", "req.ContentLength > 5000"],
        "actions": [{ "type": "deny" }],
      },
    ],
  "outbound":
    [
      {
        "name": "LogUnsuccessfulRequests",
        "expressions": ["res.StatusCode < '200' && res.StatusCode >= '300'"],
        "actions":
          [
            {
              "type": "log",
              "config":
                {
                  "metadata":
                    { "hostport": "example.com:443", "success": false },
                },
            },
          ],
      },
    ],
}

Javascript SDK Docs:

• https://ngrok.github.io/ngrok-javascript/classes/HttpListenerBuilder.html#policy

Python

with open('/path/to/policy.json') as f:
		policy = json.load(f)
		listener = await session.http_endpoint().policy(policy).listen()

policy.json

{
  "inbound":
    [
      {
        "name": "FooBarParamNotFound",
        "expressions": ["'bar' in getQueryParam('foo')"],
        "actions":
          [
            {
              "type": "custom-response",
              "config":
                {
                  "status_code": 404,
                  "content": "not found",
                  "headers": { "content-type": "text/plain" },
                },
            },
          ],
      },
      {
        "name": "BazCookieForLargeRequests",
        "expressions": ["!hasReqCookie('baz')", "req.ContentLength > 5000"],
        "actions": [{ "type": "deny" }],
      },
    ],
  "outbound":
    [
      {
        "name": "LogUnsuccessfulRequests",
        "expressions": ["res.StatusCode < '200' && res.StatusCode >= '300'"],
        "actions":
          [
            {
              "type": "log",
              "config":
                {
                  "metadata":
                    { "hostport": "example.com:443", "success": false },
                },
            },
          ],
      },
    ],
}

Python SDK Docs:

• https://ngrok.github.io/ngrok-python/http_listener_builder.html#ngrok.HttpListenerBuilder.policy

Rust

info

Traffic Policy is coming soon via rust-sdk

Kubernetes Controller

---
kind: NgrokModuleSet
apiVersion: ingress.k8s.ngrok.com/v1alpha1
metadata:
  name: policy-module
modules:
  policy:
    inbound:
      - name: FooBarParamNotFound
        expressions:
          - "'bar' in getQueryParam('foo')"
        actions:
          - type: "custom-response"
            config:
              status_code: 404
              content: not found
              headers:
                content-type: text/plain
      - name: BazCookieForLargeRequests
        expressions:
          - "!hasReqCookie('baz')"
          - "req.ContentLength > 5000"
        actions:
          - type: "deny"
    outbound:
      - name: LogUnsuccessfulRequests
        expressions:
          - "res.StatusCode != '200' && res.StatusCode != '204'"
        actions:
          - type: "log"
            config:
              metadata:
                hostport: example.com:443
                success: false
---
apiVersion: networking.k8s.io/v1
kind: Ingress
metadata:
  name: example-ingress
  annotations:
    k8s.ngrok.com/modules: policy-module
spec:
  ingressClassName: ngrok
  rules:
    - host: your-domain.ngrok.app
      http:
        paths:
          - path: /
            pathType: Prefix
            backend:
              service:
                name: example-service
                port:
                  number: 80

Behavior

Policy rules are evaluated sequentially in the order they are configured with inbound rules taking effect before the upstream server is reached and outbound rules taking effect after the upstream server responds. Whether or not the configured actions are performed is determined at runtime by the expressions.

Expression Evaluation

Policy expressions are written using the Common Expression Language (CEL). Policy expressions must evaluate to true in order for policy actions to take effect. There is no behavioral difference between adding multiple expressions to a single policy rule and having one single expression with multiple statements logically conjoined together (i.e. ["1 == 1 && 2 == 2"] is the same s ["1 == 1", "2 == 2"]).

If no expressions are specified on a policy rule, its actions will always take effect.

See expressions for variable and macro definitions.

Action Execution

If a policy's expressions are evaluated as a match against a connection, the policy's actions will be executed. If multiple actions are defined on a policy, the actions will execute sequentially.

See actions for all available actions.

Reference

Configuration

Parameter	Description
inbound	A list of policy rules that will be applied to inbound traffic in the order specified.
outbound	A list of policy rules that will be applied to outbound traffic in the order specified.
name	Policy rules can optionally be given a name for convenience.
expressions	A list of CEL expressions that filter which traffic a policy rule will apply to.
actions	A list of actions that will execute sequentially if the associated policy rule's expressions all match on the traffic.
type	The type of action.
config	The configuration details of how an action should execute. Each action has its own configuration structure.

Edges

Traffic Policy is an HTTPS Edge module which can be applied to Routes.

The Traffic Policy module can be configured via the ngrok dashboard or API.

• Traffic Policy Edge Module API Resource