Respect the global agent maxSocket property

[nscott]

Currently if someone uses an AWS service and they use SSL, http(s).globalAgent.maxSockets is ignored entirely when this new agent is created. You also can't configure maxSockets by passing in config, as that is also ignored in this case.

By default, node pools its connections. That means if you have a shared agent, and you have more than 5 connections open (because the default maxSockets is 5), you're going to block until a connection is available for use. This is particularly bad when you're trying to rapidly pull and push from something like SQS.

The simplest test is to make a queue consumer for SQS. Create 10 workers that will continually try eating off the queue, and then try sending a message with the current library. The response will take a very long time to return.

See https://gist.github.com/nscott/8735628 for an example in CoffeeScript. Run it with the current aws-sdk, and then run it with this revision. You'll see that sendMessage()'s callback hits very quickly, as opposed to waiting a very long time. receiveMessage() can also pick up on those messages faster.

A temporary, injectable solution is to overwrite the prototype. See the coffescript at https://gist.github.com/nscott/8735708.

[lsegal]

Unfortunately this patch won't actually work because we only ever create the sslAgent object one time on the first request. This means that if you adjust https.globalAgent.maxSockets mid-way through your program, you will get unexpected results-- that change will not be reflected in the SDK. I would rather not change the agent behavior to be less consistent. Fortunately there is a way to delegate the property with Object.defineProperty, so I will work on a patch based on yours that can properly delegate maxSockets (and other settings).

That said, note that you can configure maxSockets in the SDK, either by creating your own agent, or by passing the globalAgent into your client. The SDK has an httpOptions configuration value that accepts an agent object:

// use global agent
AWS.config.httpOptions = { agent: require('https').globalAgent };

// alternatively, create your own
var agent = new https.Agent();
agent.maxSockets = 10;

// optionally pass it into the client rather than globally
var s3 = new AWS.S3({httpOptions: {agent: agent}});

Note that there are reasons not to use the global agent, specifically in 0.8.x, where the rejectUnauthorized setting defaults to false, which opens you up to man-in-the-middle attacks. This is the reason the SDK does not use the globalAgent by default.

[nscott]

Uhg, maybe I'm using an outdated version of the API. I tried passing my own agent through and it never worked... Well, that would indeed fix this problem. Sorry for the trouble, and thanks.

[lsegal]

I added the above change to make the SDK respect the https.globalAgent.maxSockets setting through delegation so you should not have to pass in a custom agent at all. This will be available in the next 2.x RC release, but not 1.x, since this might not be backwards compatible.

[nscott]

Thanks, I really appreciate that @lsegal!

[lock]

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