agent.maxFreeSockets Method in Node.js

Introduction to agent.maxFreeSockets

In Node.js, the agent.maxFreeSockets property is part of the http.Agent class, introduced in version v0.11.7. It defines the maximum number of sockets that should be kept open in a free (idle) state per host. This setting is particularly useful when the keepAlive option is enabled, allowing for persistent connections and efficient reuse of sockets.

Default Behavior

By default, agent.maxFreeSockets is set to 256. This means that, when keepAlive is true, the agent will maintain up to 256 idle sockets per host. If the number of idle sockets exceeds this limit, older sockets will be closed to free up resources.

Setting agent.maxFreeSockets

You can customize the number of free sockets by setting the maxFreeSockets property when creating a new agent:

const http = require('http');

const agent = new http.Agent({
  keepAlive: true,
  maxFreeSockets: 10
});

In this example, the agent is configured to keep a maximum of 10 idle sockets per host.

Using the Agent in HTTP Requests

Once the agent is configured, you can use it in HTTP requests to manage connections:

const options = {
  hostname: 'example.com',
  port: 80,
  path: '/',
  method: 'GET',
  agent: agent
};

const req = http.request(options, (res) => {
  console.log(`STATUS: ${res.statusCode}`);
});

req.end();

This setup ensures that the specified number of idle sockets are maintained, optimizing connection reuse and resource management.

Conclusion

The agent.maxFreeSockets property in Node.js provides fine-grained control over the number of idle sockets maintained per host. By adjusting this setting, developers can optimize resource usage and improve the performance of applications that make frequent HTTP requests.