Today we are announcing that Session Affinity routing is now generally available as a fully supported part of the Heroku Platform. When Session Affinity is enabled for an app, requests from a given browser will always be routed to the same Dyno. Under the hood, the Heroku Router will add a cookie to all incoming requests from new clients; this cookie allows subsequent requests from that client to return to the same Dyno. With specific clients bound to specific Dynos, apps that depend on ‘sticky sessions’ can still take advantage of Heroku’s flexible scaling.
We introduced Session Affinity in Heroku Labs last April. Since then, many customers have built apps with the new routing strategy...