GCP Pub/Sub Message Ordering guide with Node.js - How to Ensure Consistent Processing?
I just started working with I'm maintaining legacy code that I've searched everywhere and can't find a clear answer. I'm currently working on a messaging system using GCP Pub/Sub with Node.js, and I'm working with a scenario with message ordering. Despite using a single subscription for my topic, I occasionally receive messages out of order when processing them in my Cloud Function. I'm using the `@google-cloud/pubsub` library, specifically version 2.17.0. Here's a sample of how I'm subscribing to my topic: ```javascript const { PubSub } = require('@google-cloud/pubsub'); const pubSubClient = new PubSub(); const subscriptionName = 'my-subscription'; const subscription = pubSubClient.subscription(subscriptionName); const messageHandler = message => { console.log(`Received message: ${message.id}`); // Process message message.ack(); }; subscription.on('message', messageHandler); ``` The messages I publish include a timestamp that I expect to be processed in chronological order. However, I see that sometimes older messages are processed after newer ones. I've ensured that only one instance of the Cloud Function is running at a time, so the concurrency should not be an scenario. I also tried enabling the `orderingKey` when publishing messages, but it still seems that the order is not respected. Here's how I'm publishing messages: ```javascript const publishMessage = async (data) => { const dataBuffer = Buffer.from(JSON.stringify(data)); await pubSubClient.topic('my-topic').publish(dataBuffer, {orderingKey: 'my-order-key'}); console.log('Message published.'); }; ``` When I check the logs, I don't see any behavior messages, just the entries of messages being processed in the unexpected order. Is there a best practice for ensuring message order in GCP Pub/Sub when using Node.js? Any insights or suggestions on what I'm missing here would be greatly appreciated. My development environment is Windows. Any advice would be much appreciated. I'm open to any suggestions. This is happening in both development and production on Ubuntu 22.04. Thanks for any help you can provide!