How to load a javascript file from the best source

Question

I have a few web servers in different locations and would like to load my javascript files from the fastest (nearest??) server. For example in Location A, I would expect the users to get their files from servers in that Location, but users from Location B would get their files from other servers, hopefully servers from location B, but that is not necessary.

I have found how to load javascript files conditionally, and I think that is a good start. I just need a way to find which is the best source(faster response).

Thanks,

Answer 1

Just use a CDN if you want that minimal performance advantage. This would differ a few milliseconds. There is a list of CDN on http://jquery.com/download/#using-jquery-with-a-cdn

The only advantage of using a CDN is that the user may have downloaded the jQuery library earlier from another website, so the jQuery library is reused from it's cache. If you are encountering performance problems, try profiling the website and check the ammount of time that a resource takes to run or load.

Answer 2

This isn't really a problem the client should solve. You should put your server behind a proxy that balances the load. If the proxy's bandwidth isn't enough, then I think you're out of luck. A quick and dirty solution is to do a Math.random() in the client side and choose the server based on that. It should balance the load pretty evenly.

If you were to measure the response time from the mirror servers, you would just introduce more load. Lets say, we have a way to determine the response time. You would either request the file from all servers, meaning you just made everything worse, or you would wait for server1, and if that didn't respond in time, you would move to server2. But by doing this you introduced load to server1.

Also if you were to ping the server, that isn't a real indicator if the available performance of that server. The server might be able to respond fast as the response is short and requires no real IO, but if you were to request a file that would mean possibly reading from the disk.