In this post, we will implement the most simple application where we will publish messages to Kafka from a Next.js application.

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Project Setup

First create a Next project with: 
➜  kafka-examples git:(master) ✗ npx create-next-app@latest
✔ What is your project named? … getstarted-nextjs
Creating a new Next.js app in /Users/enes/dev/kafka-examples/getstarted-nextjs.
Then create an Upstash Kafka cluster and a topic as explained here. In the cluster page, under the REST API section, copy the producer code under the tab Javascript (fetch).

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Implementation

Paste the producer code to the pages/api/hello.js as below: 
export default function handler(req, res) {
  fetch(
    "https://full-mantis-14079-us1-rest-kafka.upstash.io/produce/newtopic/MESSAGE",
    {
      headers: {
        Authorization:
          "Basic Wm5Wc2JDMzUwYVhNdE1UUXlPVDlUR2szT0ZkanZlWUhCVjlKanpvdzAzU25VdFJROjQtUi1mbXRvYWxYbm9ldTlUalFG5qZlNLd0VzRTEwWXZITWlXNjNoRmxqcVVycnE1X3lBcTRUUEdkOWM2SmJxZlE9PQ==",
      },
    }
  )
    .then((response) => response.json())
    .then((data) => {
      console.log(data);
    });

  res.status(200).json({ name: "John Doe" });
}

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Run and Deploy

Now you can test your code by running: 
npm run dev
Check: http://localhost:3000/api/hello In the logs you should see the output of Kafka like below: 
{
  "topic": "newtopic",
  "partition": 0,
  "offset": 281,
  "timestamp": 1640993860432
}