Wikimedia Apps/Team/RESTBase services for apps

The Product Infrastructure team maintains a set of Node.js services intended to provide wiki content in a form tailored to the needs of the Wikimedia mobile platforms, and in particular the Wikimedia Apps.

These services include:


 * Mobile Content Service (MCS): A service built to replace the apps' usage of the MediaWiki action API  module and to incorporate page content transforms that were previously being performed in JavaScript on the client post-page load. MCS is slated for service decommissioning in July 2023.


 * Page Content Service (PCS): The successor to the Mobile Content Service, intended to make a fuller set of page content available to a variety of clients through the Wikimedia REST API.
 * Wikifeeds: A service that provides featured wiki content in JSON format via the Wikimedia REST API.

In production, each of these services is consumed by RESTBase, which is in turn exposed to the public via the REST API.

OpenAPI/Swagger documentation: REST API (prod), MCS/PCS (labs), Wikifeeds (labs)

General ideas & goals
The idea for the services mentioned here is to provide a layer of abstraction on top of various MediaWiki action API and existing RESTBase requests, custom-made for consumption by apps. In other words, they provide a Façade which makes it easy for apps to consume content from Wikipedia. The initial main goal is to improve page load performance.

We want to achieve that through the following approaches:
 * Standard endpoint structure instead of dealing with many query parameters that can be arranged differently; less cache fragmentation.
 * Reduce amount of payload by removing unneeded content.
 * Reduce the need for separate requests by aggregating information from multiple request into fewer requests.
 * Flatten and trim JSON structures. (Again, remove unused data.)


 * Take advantage of Parsoid annotations to improve the quality of the transformations done.
 * Move DOM transformations of page content (currently done client-side) to the server.

Service usage
The service endpoints are used by the Android app. Android app users get to use them by default except for usages of zhwiki or when  is disabled in the app settings. In those two cases it falls back to using regular api.php endpoints, and some newer features which are only implemented for RESTBase users are automatically disabled. In the app developer settings you can check if RESTBase is enabled and change that if necessary.

The Wikipedia Android app uses this service to get an article's opening section, table of contents, description, lead image URL, and other article information in a single request, followed by another request for the remaining sections. Other endpoints are used to fetch content for link previews and term definitions. The Android app also uses the smart random and the aggregated feed endpoint to retrieve the data needed for the cards of the Explore feed which are not user specific.

The iOS app team is working on using the aggregated feed endpoint for the iOS app. The web team is considering using RB/MCS in the future.

Monitoring
We have a RESTBase dashboard in Grafana which shows request rates for all individual endpoints. You can choose all the endpoints related to mobile on that graph to get the metrics of how many client requests actually hit RESTBase. The requests are split to several categories: However, for external requests this represents only the cache misses while the vast majority of the requests are served by Varnish.
 * internal - the request came from the WMF cluster or Labs
 * internal_update - it’s an update request from Change-Propagation
 * external - the request came from an external user.

There's also a Grafana dashboard specifically for the mobile-sections requests.

Source
The services are in the following Gerrit repos:
 * 1) source: (Gerrit) (diffusion) (GitHub mirror)
 * 2) deploy: (Gerrit) (diffusion) (GitHub mirror) - nowadays unused and archived, see T247012

The second repo is for deployment purposes. The first repo contains the implementation of the service routes. The source repo is based on the ServiceTemplateNode project provided by the Services team.

The Swagger spec can be found in the source repo in the file. This spec must be updated when the output structure is changed since there are automated tests which verify that the output adheres to the spec.

Some settings for IntelliJ are documented for your convenience. You can also use other text editors or IDEs of course. Still, the discussion about run/debug configurations might be applicable for other IDEs, too.

Testing with the Android app
The Android app has a Developer settings screen which lets you change the backends used for both MW API calls and RESTBase/MCS calls. If you have a developer flavor of the Android apk then the Developer settings are already enabled. For other flavors you need to enable the Developer settings first. To do so go to,  , then tap seven times on the logo. Then you should get a Snackbar saying "You are now a developer!". Once enabled you can tap on the new icon in the top right of the toolbar of the Settings screen. For MCS development you'll want to change the  to utilize on the following options described in the following sections. The dialog has example URIs in the hints which can be copy&pasted to the text input form field.
 * Prod: use the production RESTBase servers (the default)
 * Beta cluster settings: (There's no specific entry here but you can get it to work using the following settings:
 * RESTBaseUriFormat (default):
 * mediaWikiBaseUriSupportsLangCode (default): enabled
 * mediaWikiBaseUri (nondefault):
 * Labs: use the labs service
 * Dev: use a local developer machine which runs MCS and possibly RESTBase, too. Note that where it says host you want to replace that with the actual hostname or IP address of the host that's running your MCS services. Some of the features (link previews, aka summary endpoint, and the aggregated feed) that are implemented directly in RESTBase don't work unless you are pointing to a local RESTBase installation. To use a local RESTBase installation change the port from the MCS port 6927 to the RB port 7231.

Setting up a local RESTBase instance
Since there is some interactions between RESTBase and MCS which make it desirable to also run RB locally sometimes (featured feed; hydration of summary data), here are some hints on how to configure RB to work with MCS.


 * 1) Clone RB
 * 2) In your new , change all occurrences of   to
 * 3) Under , change the host value for   from   to
 * 4) You may also want to consider adding the following at the top of the file to run RB in a debugger:
 * 1) Under , change the host value for   from   to
 * 2) You may also want to consider adding the following at the top of the file to run RB in a debugger:
 * 1) Start MCS (if it isn't already running)
 * 2) Start RESTBase with   or   in the restbase root directory
 * 3) RESTBase listens on port   by default.
 * 4) Test URI: http://localhost:7231/en.wikipedia.org/v1/page/mobile-sections/Cassini%E2%80%93Huygens

Setting up a local Parsoid instance
To test new Parsoid patches:


 * 1) Clone Parsoid repo
 * 2) In your new , you may want to edit the   section. For example to hook it up with a few production Wikipedias:  You may also want to consider adding the following at the top of the file to run Parsoid in a debugger:
 * 3) Start Parsoid with   in the Parsoid root directory.
 * 4) Test URI example (note the  ): http://localhost:8000/en.wikipedia.org/v3/page/html/Foobar/798652007
 * 5) Now it's time to update the MCS config file.
 * 6) * If you want MCS to talk directly talk to Parsoid instead through RESTBase then use these settings: Change the uri in  of MCS' config.dev.yaml
 * 7) * If you want to go through a local RB instance then use instead:
 * 8) Start MCS with   in the MCS folder
 * 9) Test URI: http://localhost:6927/en.wikipedia.org/v1/page/mobile-sections/Foobar/798652007
 * 1) Start MCS with   in the MCS folder
 * 2) Test URI: http://localhost:6927/en.wikipedia.org/v1/page/mobile-sections/Foobar/798652007

See also the Parsoid/Setup/RESTBase page.

Development on local machine
The README.md file in the repo has some great pointers on how to set up and use the service on a dev machine.

MW Vagrant
Enable the  role in MW Vagrant. The code is located under. To restart just the service without having to restart the whole Vagrant instance you can run: Since the Vagrant instance is self-contained you cannot access other servers. If you have a page called Foo in your Vagrant instance you can access it via the following command after sshing into the box: The log file is.

Standalone Cloud VPS testing instances
The mobileapps and wikifeeds services both have standalone, automatically updated testing instances available in Cloud VPS.

The instances are  and   in the Cloud VPS Mobile project, exposed publicly at https://mobileapps.wmflabs.org and https://wikifeeds.wmflabs.org respectively.

Each is updated and restarted automatically a few minutes after code gets merged.

Troubleshooting on Cloud VPS instance:
 * Restart the service:
 * view logs:

See setup instructions for a testing instance like these.

Beta cluster
Similarly to the beta instance on deployment-restbase0[12].deployment-prep.eqiad.wmflabs, there is now also a MCS instance deployment-mcs01.deployment-prep.eqiad.wmflabs.

You can see examples for the various endpoints running in the Beta Cluster listed with each endpoint above. Here's just one example: https://en.wikipedia.beta.wmflabs.org/api/rest_v1/page/mobile-sections/Dog.

Deployment on Production cluster
The  service (supporting MCS and PCS) is deployed on Service Cluster B, but will soon be deployed on Kubernetes by way of the deployment pipeline. The  service is already deployed to k8s on the pipeline.

Deployment process
A description of the legacy deployment process we follow for.

Deployment schedule
Deployment calendar

Deployment logs
Every once in a while someone would like to know if patch XYZ has been deployed yet. Lately we note the deployment tag in the Phab task. In addition to that here are a couple of other options to find indications of that.
 * Look for mobileapps in the Server Admin Log (or directly on ) then look up the commit message of the mentioned SHA1 in the deploy repo. This option is great for better real-time notification that a new version of MCS got deployed to production.
 * Check out the tags in the source repo:  . This happens usually a bit later.