Obviously you meant for the whole infrastructure: ruby / rails workers, Mysql, Kafka, whatever other stuff their app needs (redis, memcache, etc), loadbalancers, infrastructure monitoring, etc.
Shared Web Credentials and App Links are set in the same file: you have an .entitlements where you set on what domains you want to have applinks, webcredentials. Then the iOS downloads from those domains a signed json file where you specify what apps can do applinks or webcredentials and you can limit those actions on some paths. What booking.com did is populated the paths section will 2.4M of urls instead of using wildcards (like "hotels/*"). The effect on the iOS is the Shared Web Credentials Daemon (the file is swcd) has a bug and with high amount of data it corrupts it's own database and fails. When opening absolute urls (schema://, ex: http://) the iOS wants to pull some data from swcd which isn't running because of the corrupt database so it freezes the app opening the absolute url. From my point of view Apple is the only to be blamed (of course booking.com has been sloppy). They shipped a buggy core component (swcd) and they failed on the booking.com app approval process to detect this behavior.