http.Agent

Class: http.Agent

The HTTP Agent is used for pooling sockets used in HTTP client requests.

The HTTP Agent also defaults client requests to using Connection:keep-alive. If no pending HTTP requests are waiting on a socket to become free the socket is closed. This means that Node.js's pool has the benefit of keep-alive when under load but still does not require developers to manually close the HTTP clients using KeepAlive.

If you opt into using HTTP KeepAlive, you can create an Agent object with that flag set to true. (See the constructor options.) Then, the Agent will keep unused sockets in a pool for later use. They will be explicitly marked so as to not keep the Node.js process running. However, it is still a good idea to explicitly destroy() KeepAlive agents when they are no longer in use, so that the Sockets will be shut down.

Sockets are removed from the agent's pool when the socket emits either a 'close' event or a special 'agentRemove' event. This means that if you intend to keep one HTTP request open for a long time and don't want it to stay in the pool you can do something along the lines of:

http.get(options, (res) => {
  // Do stuff
}).on('socket', (socket) => {
  socket.emit('agentRemove');
});

Alternatively, you could just opt out of pooling entirely using agent:false:

http.get({
  hostname: 'localhost',
  port: 80,
  path: '/',
  agent: false  // create a new agent just for this one request
}, (res) => {
  // Do stuff with response
})