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For over 7 years, Pushpin used Mongrel2 for managing HTTP and WebSocket client connections. Mongrel2 served us well during that time, requiring little maintenance. However, we are now in the process of replacing it with a new project, Condure. In this article we’ll discuss how and why Condure was developed.
Zurl is an HTTP client daemon based on libcurl that makes outbound HTTP requests asynchronously. It’s super useful for invoking Webhooks. Zurl supports fire-and-forget invocation, error monitoring, and protection from evil callback URLs. Sounds pretty great, right? Let’s see how it’s done.
Mongrel2 is a fast and simple HTTP & WebSocket server that communicates to backend workers via ZeroMQ. It does one thing and does it very well, making it an ideal part of a componentized architecture. The code is event-driven, allowing it to support thousands of concurrent connections and also asynchronous behaviors. These properties are especially important to realtime applications.
Fanout has been one of the most active contributors to the Mongrel2 project over the past year, adding features such as TLS SNI and improved streaming capability. We’ve also been working on making the server easier for people to get started with. And with that, we are proud to announce official packages for Debian and Ubuntu!
I’m a big fan of ZeroMQ, the peer-to-peer message queuing system. If you’ve never heard of it before, go check out the project’s website. You may need to read the guide and then wait a day or two before it hits you, but it’s the kind of simple, brilliant technology that will eventually make you wonder, “golly, why isn’t everything built this way?” What really sold me on the concept is the Mongrel2 web server. Real-time HTTP becomes a lot easier when you can exchange requests and responses asynchronously over a message queue, and the fact that it’s peer to peer makes the approach practical and easy to scale. Fanout Cloud uses ZeroMQ for the majority of communication between server nodes and components. While Fanout Cloud does support XMPP features, it notably does not use XMPP for internal communication. More on that decision in a future article.
As Fanout needs to handle both inbound HTTP and outbound HTTP, I thought it would be neat to try and write essentially the inverse of Mongrel2. The result is Zurl, an event-driven server that makes HTTP requests. The software has been released as open source, so it is free to download and use on your own machines.