Business listings and review site Yelp has made a surprise contribution to the open-source software world by releasing an internal Docker and Apache Mesos-based platform-as-a-service to the Apache Software Foundation.

Yelp engineer Kyle Anderson provides a detailed look at the machinations of its custom-made PaaS, which it calls PaaSTA, in this blog post, describing in-depth how the different parts of the stack fit together.

In the blog post, Anderson notes that Yelp has been running the bulk of its microservices on PaaSTA for the last 18 months. The platform is built on an array of open-source projects including Docker and Mesos, plus Marathon and Sensu, he explains. The main components are Docker Apache Mesos, open-source technologies used for containerizing, deploying, and scheduling software. Sensu, meanwhile, is an open-source monitoring tool that ensures everything is running smoothly, while Marthon works to keep services up and running after deployment. Should a service crash somewhere, Marathon automatically spins it up again so users experience no interruption.

“Marathon makes sure that you have copies of a service available at all times so the service will stay up and running,” Anderson wrote.

The PaaSTA PaaS is therefore a combination of the above four tools that serves as a platform to create a build, deploy, and run system, entwined by Yelp’s custom-made connective tissue.

The system relies heavily on Docker containers, which serve as the building blocks used by Yelp’s developers to package code, which is then run on either Yelp’s bare-metal servers or Amazon Web Services. Once an app has been deployed, PaaSTA works to keep it up and running.

In an interview with Fortune, Yelp’s Anderson said that since implementing PaaSTA, the company’s developers have been afforded a lot more free time to actually sit down and develop things. The platform has also greatly improved Yelp’s search capabilities, Anderson claimed.

“Search is so hard that you have to have a big internal team to handle it but now that they’re on PaaSTA, the developers don’t have to worry about servers or the number of copies running. That is handled for them,” Anderson said. “When you don’t need humans to worry about underlying infrastructure, they are freed up to do other things.”

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