Clojure and the MailOnline

Rewriting the MailOnline

Clojure and the MailOnline

March 25, 2015
Jon Pither
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In 2013 the worlds busiest newspaper website was rewritten in Clojure. The incumbent CTO Clifton Cunningham had the technology vision of a replacement front-end system written using a functional programming language, that would yield the benefits of being much simpler and easier to maintain.

The new system would have to faster be than the existing Java solution, and be more robust and less error prone. The business wanted a platform that could cater for providing different views of content to different devices, and so extensibility was crucial.

Jon Pither of JUXT led a team to rewrite the newspaper website in Clojure from scratch against these requirements, using data primarily held in ElasticSearch. The team initially started with a handful of developers, flexing up to twelve over time, as a variety of satellite services and separate systems were incorporated into the redevelopment. JUXT ran a series of training courses to help developers make the transition to Clojure.

After a short period of months, the new website ran alongside the legacy one. A custom built diagnostics and HTML comparison framework was also deployed into production to give vital guarantees about the content being rendered.

The new codebase was conservatively an order of magnitude smaller than its Java / Object Oriented counterpart and made a seamless deployment into production. This contrasts against a previously attempted rewrite using a modern Java EE stack that was cut short.

The developers working on the project were a happy bunch, and the project had a feel good factor about it. Whilst the Clojure project was going on a number of modern content authoring tools were built using Node.js, and the CTO describes the overall journey here, at a Node conference.