Google (GOOG) has lost an important member of its Google App Engine team. Peter Magnusson, who was director of engineering and the lead of Google App Engine, has left the company to join photo messaging startup Snapchat.

Magnusson spent nearly 3 and a half years working at Google before moving on. During that time, he ran the company’s entire engineering efforts and worked on its cloud computing strategy in several products groups.

Under his engineering leadership, Google App Engine grew to more than 4 million registered applications and more than 300,000 active developers. It’s one of Google’s largest products, so the loss of such a senior executive must be placing some burden on Google.

Interestingly, Snapchat is one of Google App Engine’s largest customers. According to reports, Snapchat’s reliance on Google isn’t likely to change, even though Snapchat will continue to evaluate alternatives.

Google App Engine is Google’s platform-as-a-service (PaaS) offering that provides customers with development and hosting services for web applications that are hosted in Google’s data centers. It provides automatic scaling for applications, as well as a sandbox for apps to be tested.

As a cloud service, it’s also had a pretty stellar track record for uptime. Google has noted in the past that it’s the service that doesn’t go down, although it has had its hiccups with unscheduled downtime on rare occasions.

Who will fill Magnusson’s shoes at Google is so far unknown.