When Automation Fights Back: Split Brains, Lightning Strikes, and SLOs at Scale
When Automation Fights Back (Jan 2018 – Mar 2019) By 2018 the industry had automated failover, orchestration, and recovery — and the defining postmortems of this window are about that automation making the wrong call. The question shifted from “why did the component fail?” to “why did our self-healing make it worse?” The incidents that defined the period TSB Bank migration, April 2018 — A big-bang core-banking migration locked UK customers out of accounts for weeks. The subsequent independent review became required reading on cutover risk, and regulators started treating operational resilience as a compliance domain. GitHub, October 21, 2018 — 43 seconds of network partition between US East and West Coast datacenters; orchestration software promoted a West Coast MySQL primary while the East Coast primary still held unreplicated writes. Split-brain. GitHub chose data consistency over uptime, running degraded for ~24 hours, and published a superb hour-by-hour analysis (github.blog). Microsoft Azure South Central US, September 2018 — A lightning strike caused a cooling failure; hardware shut down to protect itself, and the regional outage revealed how many “global” Azure services (including Azure AD and the status portal) had hidden dependencies on one region. Google Cloud, July 2018 — A global load-balancing configuration event briefly broke customers worldwide, feeding a growing theme: global control planes mean global blast radius. Facebook, March 13, 2019 — A ~14-hour outage of Facebook, Instagram, and WhatsApp attributed to a server configuration change — at the time the longest outage in the company’s history. Wells Fargo, February 2019 — A fire-suppression system triggered a datacenter shutdown, and banking customers lost app and card access. Banks officially had SRE-shaped problems. What the postmortems reveal 1. Automated failover needs a theory of data. GitHub’s incident became the case study: failover automation that optimizes for availability can silently sacrifice consistency. Postmortems started asking “what does our orchestrator do during a partition?” — a Jepsen-style question applied to ops tooling. ...