MediaWiki version: 1.35.0-wmf.5
Cannot access the database: Unknown error (10.64.48.153)
Saw a surge of these and similar on rolling 1.35.0-wmf.8 to group 1. This led to cascading failures and a massive spike in errors.
Incident report: https://wikitech.wikimedia.org/wiki/Incident_documentation/20191204-MediaWiki
Several folks have theories as to what's going on here. It's possible this duplicates something else or doesn't really touch on the underlying cause; I'm just getting it filed ASAP.