I recently review an engaging post on LinkedIn Engineering’s blog entitled “TCP over IP Anycast – Pipe dream or Reality?” The authors report a plan to optimize a opening of www.linkedin.com. The web site is served from mixed web server instances located in LinkedIn’s POPs all over a world. Previously LinkedIn used DNS geomapping exclusively to track a users to a best web server instance, though a post describes how they attempted regulating BGP routing instead. In a tranquil experiment, they published a singular anycast residence analogous to each instance of their web site worldwide and let BGP routing approach users to a best one. Performance wasn’t zodiacally softened and worsened in some cases. They finished adult regulating a multiple of DNS and BGP routing to approach users to a best place. Rather than use a singular anycast IP residence for each instance worldwide, they grouped their POPs by embankment and reserved an anycast residence to all a instances within a region. When a user visits www.linkedin.com, DNS geomapping techniques approach her to a suitable anycast IP for her region, and afterwards BGP routing chooses a trail to a best web server instance in that region. LinkedIn’s before and after opening measurements uncover a examination was a success.
This post raises an apparent question: are techniques regulating DNS to “steer” trade (such as IP geolocation) sufficient, or do we need to cruise regulating anycast as LinkedIn did? The brief answer is that DNS steering works good and is customarily removing better.
LinkedIn’s conditions is special: they run a 14th busiest web site in a universe according to Alexa. They have a resources and engineering talent to build their possess worldwide network of POPs to offer all that traffic. Few companies can do similar, nor do they need to. The advantages of anycasted web calm customarily start to matter in a conditions such as LinkedIn’s with a vast series of content-serving instances. Most companies have calm distributed to distant fewer sites and will be many improved served by regulating DNS steering techniques.
Let’s residence some of a specific issues that LinkedIn cites per regulating DNS to approach users. First, they indicate out a miss of prominence to a tangible user’s IP residence to make steering decisions. Recall that finish user inclination send DNS queries to a recursive nameserver, customarily run by their ISP or on a corporate network. The recursive server queries a lawful server (in this instance a nameserver for linkedin.com) on a user’s behalf, and so any DNS steering decisions in a lawful server are done formed on a recursive server’s address, not a finish user’s address. Usually a recursive server is tighten to a user, though not always, generally in a box of vast open DNS providers, such as Google Public DNS or OpenDNS.
The good news is that a DNS engineering village has famous about a emanate for a prolonged time and there’s a solution: EDNS Client Subnet, or ECS. This DNS custom prolongation allows a recursive server to pass a user’s subnet residence to a lawful server, finally giving a lawful server prominence to a tangible finish user address. (The subnet is sent rather than a specific IP residence for remoteness reasons.) ECS is circuitous a approach by a IETF standards routine and has already seen far-reaching deployment: vital DNS providers such as Google and OpenDNS — a ones whose users are many geographically distributed — already support it. So a emanate of a lawful server not meaningful a finish user’s residence to make accurate steering decisions is going divided quickly.
The second DNS-related emanate LinkedIn mentioned was correctness of IP geolocation databases. It doesn’t do many good if a lawful server has prominence to a finish user’s tangible residence though a geographic mapping for that residence is incorrect. There are several commercially accessible IP geolocation databases and they all have their faults, that is since Dyn has built a possess to energy a products. We start with blurb information though afterwards enlarge and labour with several patent-pending exclusive techniques.
Ultimately regulating DNS to drive users to calm gives we a many flexibility. When we rest on anycast and BGP routing, your options for control are limited. You’re relying on a routing process of other people’s networks and some things are only outward your control. For example, blurb arrangements and disagreements between ISPs can means trade to take suboptimal paths. But with DNS, we can use any criteria we wish to track traffic. IP geolocation is renouned since it performs well, though there are other options. For example, Dyn offers a genuine user monitoring (RUM) use that measures CDN and web site opening from inside a web browser of tangible users (hence a name).
So while adding anycast to your web site can offer good performance, eventually DNS steering gives we a many flexibility.
By Matt Larson, Chief Technology Officer during Dyn
Related topics: DNS