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Sampling traffic

Arcjet is designed to run on every request. When testing your rules, you can use DRY_RUN mode to see how your rules would behave without actually enforcing them. The result will be logged, but all requests will be allowed. This is useful for testing your rules without affecting your users.

You can also write a simple sampling function to set the Arcjet rules using withRule based on a desired sample rate. This allows you to test your rules on a subset of your traffic.

This Next.js middleware example shows how to trigger Arcjet Shield and bot detection rules in live mode on 10% of your traffic.

/middleware.ts
import arcjet, { detectBot, shield } from "@arcjet/next";
import { NextRequest, NextResponse } from "next/server";


export const config = {
  // matcher tells Next.js which routes to run the middleware on. This runs
  // the middleware on all routes except for static assets.
  matcher: ["/((?!_next/static|_next/image|favicon.ico).*)"],
};


const sampleRate = 0.1; // 10% of requests


const aj = arcjet({
  key: process.env.ARCJET_KEY!,
  // You could include one or more base rules to apply to all requests
  rules: [],
});


function shouldSampleRequest(sampleRate: number) {
  // sampleRate should be between 0 and 1, e.g., 0.1 for 10%, 0.5 for 50%
  return Math.random() < sampleRate;
}


// Shield and bot rules will be configured with live mode if the request is
// sampled, otherwise only Shield will be configured with dry run mode
function sampleSecurity() {
  if (shouldSampleRequest(sampleRate)) {
    console.log("Rule is LIVE");
    return aj
      .withRule(
        shield(
          { mode: "LIVE" }, // will block requests if triggered
        ),
      )
      .withRule(
        detectBot({
          mode: "LIVE",
          allow: [], // "allow none" will block all detected bots
        }),
      );
  } else {
    console.log("Rule is DRY_RUN");
    return aj.withRule(
      shield({
        mode: "DRY_RUN", // Only logs the result
      }),
    );
  }
}


export default async function middleware(request: NextRequest) {
  const decision = await sampleSecurity().protect(request);


  if (decision.isDenied()) {
    if (decision.reason.isBot()) {
      return NextResponse.json({ error: "You are a bot" }, { status: 403 });
    } else if (decision.reason.isShield()) {
      return NextResponse.json({ error: "Shields up!" }, { status: 403 });
    } else {
      return NextResponse.json({ error: "Unauthorized" }, { status: 403 });
    }
  } else {
    return NextResponse.next();
  }
}