High Availability at Heroku Mark McGranaghan Scale & Scope O(1,000) instances O(1,000,000) apps Success & Failure Architecture Execution Architecture Execution Platform-Enabled HA Routing Crashes & Supervision Crashes as the only code path Crashes as a hot code path Error Kernel Layered design Message passing... {slug: “https://aws...”, cmd: “java ...”, env: {“JAVA_O