The mobileapps service (a.k.a. "mobile content service") provides a facade through which Wikimedia page content is requested, modified to remove unnecessary bits, and put into a form tailored for use by mobile clients. The underlying content is primarily Parsoid HTML fetched via the REST API, modified, and then stored in RESTBase for retrieval via the
Mobileapps runs on Service Cluster B alongside a number of other node.js services. Use of content provided by mobileapps was rolled out incrementally to Wikipedia Android app users in early 2016. The service currently provides article content for all users of the Android app, with certain exceptions.
In addition to the page content, the mobileapps service also provides data for various Explore feed features in both Android and iOS apps. The Explore feed features consist of a general featured feed (comprising of TFA, Picture of the day, most read pages of the previous day, and In the news), On This Day, and wiki and country specific announcements for surveys or fundraising.
In the near future the /page/summary endpoint in RESTBase will use this service's implementation. The /page/summary endpoint is also used by web for page previews.
The mobileapps service is maintained primarily by the Wikimedia Reading Infrastructure team, with support from the Services team. Mentioning mobileapps in IRC on the ops channel should get their attention.
Consequences of shutdown/failure
The Android app has implemented a fallback mechanism in which it will temporarily revert to loading content via the action API after a "significant" REST API failure (a page load error other than a 404 or client-side networking error). After falling back, the app will wait for 100 successful requests and then again attempt a request from the mobile content service, falling back again in case of error.
For page loads, the app should behave identically from the user's perspective after falling back to the action API. However, the Wiktionary definition lookup feature requires the mobile content service, and will not be available if the service is unavailable.
A failing mobileapps service could also significantly reduce the content available in the native apps' Explore feed.
Wikimedia REST API mobile endpoints (link is to enwiki, but the endpoints are the same for all Wikipedias)
Refresh RESTBase cache for mobileapps for troubleshooting and fighting vandalism tips