Happy Eyeballs

Geoff Huston wrote up a very interesting analysis of the RFC 6555 “Happy Eyeballs” features being added to web browsers recently.

As these features reach the mainstream stable browser releases and more people being using them Squid in the role of intercepting proxy are starting to face the same issues mentioned for CGN gateways. For all the same reasons. Whether or not you are operating an existing interception proxy or installing a new one this is one major new feature of the modern web which needs to be taken into account when provisioning the network and Squid socket/FD resources.

Squid operating as forward proxy do not face this issue as each browser only opens a limited number of connections to the proxy. Although Firefox implementation of the  “Happy Eyeballs” algorithm appears to have been instrumental in uncovering a certain major bug in Squids new connection handling recently.

A Squid Implementation

For those interested, Squid-3.2 does implement by default a variation of the “Happy Eyeballs” algorithm.

DNS lookups are performed in parallel now, as opposed to serial as they were in 3.1. As a result the maximum DNS lookup time is reduced from the sum of A and AAAA response times, to the maximum of both.

TCP connection attempts are still run in serial, but where older versions of Squid interspersed a DNS lookup with each set of TCP attempts the new 3.2 code identifies all the possible destinations first and tries each individual address until a working connection is found. Retries under the new version are also now limited per-address where in the older versions each retry meant a full DNS result set of addresses was re-tried.

As a result dns_timout is separated from connect_timeout which is now fully controlling only one individual TCP connection handshake.