node-reusing-connections.md

Reusing connections with keep-alive in Node.js

By default, Node.js default HTTP/HTTPS agent creates a new TCP connection for every new request. By not reusing already created connections, we incur the cost of establishing new ones, which includes 3-way or 7-way handshake depending on whether this is an HTTP or HTTPS transaction. We are also not going to leverage the actual throughput established by the TCP protocol’s flow and congestion controls.

For short-lived operations completing within a single-digit ms (like DynamoDB queries) the latency overhead of setting up a TCP connection might be greater than the operation itself. Additionally, DynamoDB encryption at rest is integrated with AWS KMS and you may experience latencies from the database having to re-establish new AWS KMS cache entries for each operation (read more).

The easiest way to configure aws-sdk-js to reuse TCP connections is to set the AWS_NODEJS_CONNECTION_REUSE_ENABLED environment variable to 1. This feature was added in the 2.436.0 release.

Alternatively, an HTTP or HTTPS agent can be supplied with keepAlive set to true.

Example of setting it globally:

const AWS = require('aws-sdk');

// http or https as per your use case
const http = require('http');
const agent = new http.Agent({
  keepAlive: true
});

AWS.config.update({
  httpOptions: {
    agent
  }
});

Example of setting keepAlive on a per-client basis:

const AWS = require('aws-sdk')

// http or https as per your use case
const https = require('https');
const agent = new https.Agent({
  keepAlive: true
});

const dynamodb = new AWS.DynamoDB({
  httpOptions: {
    agent
  }
});

If the keepAlive option is enabled, you can also set the initial delay for TCP Keep-Alive packets with keepAliveMsecs, which by default is 1000ms (refer to Node.js official docs for more details).