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Use Serverless Kafka to Produce Events in AWS Lambda

In this tutorial, we will produce events to Upstash Kafka from an AWS Lambda function.

Create Kafka

First, create an Upstash Kafka cluster and topic following those steps. You will need the endpoint, username and password in the following steps.

Create Project

We will use Serverless Framework to create the application.

kafka-examples git:(master) serverless
What do you want to make? AWS - Node.js - HTTP API
What do you want to call this project? produce-in-lambda
Downloading "aws-node-http-api" template...
Project successfully created in produce-in-lambda folder

Then we will initialize a node project and install axios dependency.

npm init
npm install axios

Implement the Lambda Function

Open the handler.js and update as below:

const fetch = require('axios').default;

module.exports.hello = async (event) => {
const msg = "Hello"
const address = "https://REPLACE_YOUR_ENDPOINT"
const auth = Buffer.from(`${user}:${pass}`).toString('base64')
const response = await fetch(`${address}/produce/newtopic/${msg}}`, {
headers: {
Authorization: `Basic ${auth}`
const res =

return {
statusCode: 200,
body: JSON.stringify(
header: "Pushed this message to Upstash Kafka with REST API!",
message: msg,
response: res,

You need to replace the endpoint, username and password above with the values that you copy from the Upstash Console.

The above code simply creates a producer and sends the message to Kafka.

Deploy the Lambda Function

You can deploy your function to AWS by running:

serverless deploy

This command will output your URL. The output should be something like this:

"header": "Pushed this message to Upstash Kafka!",
"message": {
"value": "Hello message"

Test the Function

Now let’s validate that the messages are pushed to Kafka. We can consume the Kafka topic using the REST API. You can copy the curl code to consume from the Upstash Console.

produce-in-lambda git:(master) ✗ curl -u REPLACE_USER_NAME:REPLACE_PASSWORD

[ {
"topic" : "newtopic",
"partition" : 0,
"offset" : 98,
"timestamp" : 1639610767445,
"key" : "",
"value" : "Hello message",
"headers" : [ ]
} ]%

REST vs Kafka Client

We can also use a native Kafka client (e.g. KafkaJS) to access our Kafka cluster. See the repo for both examples. But there is a latency overhead if connecting (and disconnecting) to the Kafka with each function invocation. In our tests, the latency of the function with REST is about 10ms where it is about 50ms when KafkaJS is used. Kafka client's performance could be improved by caching the client outside the function but it can cause other problems as explained here.

Troubleshooting: If Lambda function outputs internal error, check the cloudwatch log (Lambda > Monitor > View logs in CloudWatch)