Traffic 101: Packets Mostly Flow

This post details the foundational architecture of Slack's edge network request flow. It explains how user requests are routed from globally distributed edge PoPs to the main AWS us-east-1 region. Key technical details include the DNS resolution process using Route53 and NS1 with EDNS Client Subnet (ECS), the role of Network Load Balancers (NLBs) in pass-through mode, and the separation of websocket traffic (ingested via 'envoy-wss') from non-websocket API traffic (ingested via 'envoy-edge'). It also describes failover mechanisms for websocket connections using primary and backup DNS records and the concept of a degraded mode for clients when websocket connections fail. For API traffic, it outlines routing to services like 'Supra/Miata', 'Imgproxy', and 'Envoy-www'.