Load balancing geographically distributed nodes with varnish - a good idea?

Adrian Otto aotto at mosso.com
Thu Sep 15 18:10:19 CEST 2011


I agree with Artur that DNS is a good place to decide where you want to route people on a global basis in a situation where you have a temporary regional overload. That's how most CDN networks solve that issue. You could use an API controlled DNS service like Route 53 from AWS, and when you detect the congestion condition, adjust the DNS records to respond with alternate IP addresses that have adequate capacity available. You will need to use a DNS TTL with a relatively low value, perhaps in the 10 minute range. This should allow you to automatically shed load away from your congested sites.


On Sep 15, 2011, at 8:32 AM, Thomas Prommer wrote:

> Varnish Community,
> We are managing a cluster farm of 6 nodes that are geographically distributed across Europe (Amsterdam, London, Lisbon, Frankfurt, Zurich, Milan) delivering our internationalized application for the appropriate CCTLD for such nodes. All nodes have the same server image and application deployed. The server distribution is critical to ensure low latency in local markets as well as for SEO reasons.
> The application is a simple LAMP application (no centralized data) that is using Varnish and Lighttpd Fast CGI for optimal scaling. However, we still run into scaling issues were essentially one node gets hit hard with local traffic while all the other severs are pretty idle.
> Our question is if there is a common recommendation of load balancing a server cluster where the servers are geographically distributed and also if varnish or the lighttpd fastcgi server would be more appropriate to carry out the load balancing?
> We know that both systems allow for load balancing but we are concerned that simply load balancing the IPs of geographically servers wouldn't perform too well because an additional round trip to a remote server location would be introduced.
> In a nutshell, our questions are:
> Are there any good strategies around load balancing geographical distributed servers?
> What are the evaluation points for deciding if either Varnish or Lighttpd FastCGI would be more appropriate to own the load balancing responsibility?
> Thanks /Thomas
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