AWS Lambda with pg Pool and RDS Proxy: "Connection terminated unexpectedly" when processing SQS messages

Question

---

We are using pg Pool in our Lambda function.

Our connectDb function looks like this:

const config = {
  database,
  user: username,
  password,
  max: max_pool,
  idleTimeoutMillis,
  connectionTimeoutMillis,
};

if (!pool) {
  pool = new Pool(config);
}
client = await pool.connect();

return client;

---

And this is how the Lambda handler looks like:

import { Client } from "pg";
import { sqs } from "./sqsClient"; // just for example

let dbClient: Client;

exports.handler = async (event, context) => {
  context.callbackWaitsForEmptyEventLoop = false;

  try {
    const markQueueStatusAndDeleteMessage = async (
      message: any,
      QUEUE_URL: any,
      dbClient: any,
      queue_status_update_query: any,
      query_dyanamic_values: any = []
    ) => {
      // Delete processed message from the queue
      const deleteParams = {
        QueueUrl: QUEUE_URL,
        ReceiptHandle: message.receiptHandle,
      };

      console.log("deleting message from queue...");
      await sqs.deleteMessage(deleteParams).promise();
      console.log("deleted message from queue...");

      console.log(queue_status_update_query);

      if (query_dyanamic_values.length > 0) {
        await dbClient.query(queue_status_update_query, query_dyanamic_values);
      } else {
        await dbClient.query(queue_status_update_query);
      }

      console.log(
        "CREATE-ORDER-PROCESSOR-ERROR: ",
        queue_status_update_query
      );
    };

    console.log(
      "Records Length: ",
      event.Records.length,
      "Processing messages..."
    );

    for await (const message of event.Records) {
      try {
        context.callbackWaitsForEmptyEventLoop = false;

        if (!dbClient) {
          dbClient = await connectPostgresDb();
        }

        // then all the processing...
        // we aren’t using any release() or end().
        // we are using RDS Proxy with 10min timeout.

      } catch (err) {
        console.error("Error processing message:", err);
      }
    }
  } catch (err) {
    console.error("Handler error:", err);
  }
};

---

The Issue

We’re getting the following error:

Error: Connection terminated unexpectedly
    at Connection.<anonymous> (/app/node_modules/pg/lib/client.js:132:73)
    at Object.onceWrapper (node:events:631:28)
    at Connection.emit (node:events:517:28)
    at Connection.emit (node:domain:489:12)
    at Socket.<anonymous> (/app/node_modules/pg/lib/connection.js:63:12)
    at Socket.emit (node:events:517:28)
    at Socket.emit (node:domain:489:12)
    at TCP.<anonymous> (node:net:350:12)
Emitted 'error' event on Client instance at:
    at Client._handleErrorEvent (/app/node_modules/pg/lib/client.js:341:10)
    at Connection.<anonymous> (/app/node_modules/pg/lib/client.js:150:16)
    at Object.onceWrapper (node:events:631:28)
    [... lines matching original stack trace ...]
    at TCP.<anonymous> (node:net:350:12)

Node.js v18.20.8

---

Question

• Is this error happening because the connection is not being returned to the pool (since we don’t call release())?
• Or is it due to the RDS Proxy timing out / killing the connection?

This is an SQS queue Lambda that processes batches of messages. Ok so i checked an the issue wasnt only in the lambda function but also our nestjs server.. but we are properly releasing the connection there

nestjs config

    this.readPool = new Pool({
      user: this.configService.get('database.username'),
      host: this.configService.get('database.hostRead'), // Reader instance
      database: this.configService.get('database.name'),
      password: this.configService.get('database.password'),
      port: this.configService.get('database.port') || 5432,
      max: this.configService.get('database.max_pool') || 100,
      idleTimeoutMillis: this.configService.get('database.idleTimeoutMillis') || 30000,
      connectionTimeoutMillis: this.configService.get('database.connectionTimeoutMillis') || 2000
    });

so is anyone of these causing trouble for the other? can anyone help with this