Comments on: Using CNAMES to get around browser connection limits http://ajaxian.com/archives/using-cnames-to-get-around-browser-connection-limits Cleaning up the web with Ajax Thu, 17 May 2012 07:43:39 +0000 hourly 1 http://wordpress.org/?v=3.3.2 By: Annonymous http://ajaxian.com/archives/using-cnames-to-get-around-browser-connection-limits/comment-page-1#comment-258258 Annonymous Mon, 05 Nov 2007 15:34:05 +0000 http://ajaxian.com/?p=1944#comment-258258 Question: What happens when you use this strategy in a HTTPS site? Will the browser prompt with a warning saying that this page contains content from other sites? Question: What happens when you use this strategy in a HTTPS site? Will the browser prompt with a warning saying that this page contains content from other sites?

]]> By: Steve Souders http://ajaxian.com/archives/using-cnames-to-get-around-browser-connection-limits/comment-page-1#comment-245525 Steve Souders Fri, 22 Dec 2006 23:09:57 +0000 http://ajaxian.com/?p=1944#comment-245525 Using CNAMEs is a way to increase download parallelization without users having to change their configuration settings. The issue of increased DNS lookups has already been mentioned. In my research another issue is the amount of thrashing on the client. I tried using different numbers of CNAMEs: 1, 2, 4, and 10. Using 2 was the best. Using 4 and 10 were worse than 1. As far as the browser config settings go, IE and Firefox are very different. In Firefox, the number of downloads that can happen for a single server depends on what version of HTTP is used. For HTTP/1.0 it is network.http.max-connections-per-server (defaults to 8). For HTTP/1.1 it's network.http.max-persistent-connections-per-server (defaults to 2). This example is using HTTP/1.1, therefore max-persistent-connections-per-server is a gating factor in the number of simultaneous downloads that is achieved. Before thinking of increasing this configuration setting, or using more than 2 CNAMEs, keep in mind another configuration setting that comes into play: network.http.max-connections (defaults to 24). You can never achieve more than 24 simultaneous downloads. For example, if you had 40 images across 20 CNAMEs, you would hope to get 40 parallel downloads. In actuality, only 24 images would be downloaded in parallel. IE, on the other hand, does not have a limit on the maximum number of parallel downloads. At least, not that I've found. I've been able to perform over 100 downloads in parallel (limited to two per hostname for HTTP/1.1, four per hostname for HTTP/1.0). Using CNAMEs is a way to increase download parallelization without users having to change their configuration settings. The issue of increased DNS lookups has already been mentioned. In my research another issue is the amount of thrashing on the client. I tried using different numbers of CNAMEs: 1, 2, 4, and 10. Using 2 was the best. Using 4 and 10 were worse than 1.

As far as the browser config settings go, IE and Firefox are very different. In Firefox, the number of downloads that can happen for a single server depends on what version of HTTP is used. For HTTP/1.0 it is network.http.max-connections-per-server (defaults to 8). For HTTP/1.1 it’s network.http.max-persistent-connections-per-server (defaults to 2). This example is using HTTP/1.1, therefore max-persistent-connections-per-server is a gating factor in the number of simultaneous downloads that is achieved. Before thinking of increasing this configuration setting, or using more than 2 CNAMEs, keep in mind another configuration setting that comes into play: network.http.max-connections (defaults to 24). You can never achieve more than 24 simultaneous downloads. For example, if you had 40 images across 20 CNAMEs, you would hope to get 40 parallel downloads. In actuality, only 24 images would be downloaded in parallel.

IE, on the other hand, does not have a limit on the maximum number of parallel downloads. At least, not that I’ve found. I’ve been able to perform over 100 downloads in parallel (limited to two per hostname for HTTP/1.1, four per hostname for HTTP/1.0).

]]> By: Michael Schwarz http://ajaxian.com/archives/using-cnames-to-get-around-browser-connection-limits/comment-page-1#comment-245415 Michael Schwarz Wed, 20 Dec 2006 11:52:18 +0000 http://ajaxian.com/?p=1944#comment-245415 I have done this years ago already, not only because of the 2 concurrent connection default limit. My problem sometimes was that you have more DNS lookups which was slow in some countries or with bad configured DNS servers. I have done this years ago already, not only because of the 2 concurrent connection default limit. My problem sometimes was that you have more DNS lookups which was slow in some countries or with bad configured DNS servers.

]]> By: Ryan Breen http://ajaxian.com/archives/using-cnames-to-get-around-browser-connection-limits/comment-page-1#comment-245411 Ryan Breen Wed, 20 Dec 2006 03:18:59 +0000 http://ajaxian.com/?p=1944#comment-245411 Andy, looking at my Firefox settings, the 8 connections is for maximum connections to a host. There is a separate line for maximum persistent connections (the HTTP 1.1 connections I'm discussing here), and that is set to 2 in my Firefox. Andy, looking at my Firefox settings, the 8 connections is for maximum connections to a host. There is a separate line for maximum persistent connections (the HTTP 1.1 connections I’m discussing here), and that is set to 2 in my Firefox.

]]> By: See Also http://ajaxian.com/archives/using-cnames-to-get-around-browser-connection-limits/comment-page-1#comment-245407 See Also Tue, 19 Dec 2006 23:56:37 +0000 http://ajaxian.com/?p=1944#comment-245407 http://www.die.net/musings/page_load_time/ http://www.die.net/musings/page_load_time/

]]> By: Barry http://ajaxian.com/archives/using-cnames-to-get-around-browser-connection-limits/comment-page-1#comment-245398 Barry Tue, 19 Dec 2006 20:30:53 +0000 http://ajaxian.com/?p=1944#comment-245398 If your server gets too busy, you can point some of the CNAME DNS entries to another server, which serves just static content. Or if you don't have another web server, then to Amazon S3 for static content or even to an Amazon EC2 instance. It would be even cooler if it could be done based on server load. If your server gets too busy, you can point some of the CNAME DNS entries to another server, which serves just static content. Or if you don’t have another web server, then to Amazon S3 for static content or even to an Amazon EC2 instance.

It would be even cooler if it could be done based on server load.

]]> By: Andy Kant http://ajaxian.com/archives/using-cnames-to-get-around-browser-connection-limits/comment-page-1#comment-245397 Andy Kant Tue, 19 Dec 2006 20:29:24 +0000 http://ajaxian.com/?p=1944#comment-245397 Interesting note...Firefox may default to its max of 8 connections now. I haven't modified the value in Firefox 2 and I don't have Fasterfox installed, but my setting is at 8 anyways. Interesting note…Firefox may default to its max of 8 connections now. I haven’t modified the value in Firefox 2 and I don’t have Fasterfox installed, but my setting is at 8 anyways.

]]> By: Andy Kant http://ajaxian.com/archives/using-cnames-to-get-around-browser-connection-limits/comment-page-1#comment-245396 Andy Kant Tue, 19 Dec 2006 20:27:18 +0000 http://ajaxian.com/?p=1944#comment-245396 Kris: They aren't limited to 2 connections but they default to 2. This value can be increased in both browsers but the average user isn't going to know how so you need to assume they only have 2. Kris: They aren’t limited to 2 connections but they default to 2. This value can be increased in both browsers but the average user isn’t going to know how so you need to assume they only have 2.

]]> By: Kris Zyp http://ajaxian.com/archives/using-cnames-to-get-around-browser-connection-limits/comment-page-1#comment-245395 Kris Zyp Tue, 19 Dec 2006 20:22:11 +0000 http://ajaxian.com/?p=1944#comment-245395 Yes, this is an important performance tip. However, I was under the impression that Firefox had (single host) connection limit of 4 and just IE limited at 2. Is it true that both IE and Firefox limit at 2? Yes, this is an important performance tip. However, I was under the impression that Firefox had (single host) connection limit of 4 and just IE limited at 2. Is it true that both IE and Firefox limit at 2?

]]> By: Oliver Tse http://ajaxian.com/archives/using-cnames-to-get-around-browser-connection-limits/comment-page-1#comment-245394 Oliver Tse Tue, 19 Dec 2006 20:04:15 +0000 http://ajaxian.com/?p=1944#comment-245394 Great article! I love these performance ones! Thanks! Great article! I love these performance ones! Thanks!

]]> By: Mark Holton http://ajaxian.com/archives/using-cnames-to-get-around-browser-connection-limits/comment-page-1#comment-245393 Mark Holton Tue, 19 Dec 2006 19:21:13 +0000 http://ajaxian.com/?p=1944#comment-245393 Why is it always the anonymous ones who bash and run?! Thanks for the info Why is it always the anonymous ones who bash and run?!
Thanks for the info

]]> By: Ryan Breen http://ajaxian.com/archives/using-cnames-to-get-around-browser-connection-limits/comment-page-1#comment-245391 Ryan Breen Tue, 19 Dec 2006 17:23:32 +0000 http://ajaxian.com/?p=1944#comment-245391 Google Maps works this way, so I think large sites can make judicious use of this technique without fear. A poster on the blog pointed out that you can get the same effect with a wildcard DNS entry rather than explicit CNAMEs. That's certainly true -- we just couldn't figure out how to enable wildcard DNS through our provider for this specific example. :-) Google Maps works this way, so I think large sites can make judicious use of this technique without fear.

A poster on the blog pointed out that you can get the same effect with a wildcard DNS entry rather than explicit CNAMEs. That’s certainly true — we just couldn’t figure out how to enable wildcard DNS through our provider for this specific example. :-)

]]> By: Alex http://ajaxian.com/archives/using-cnames-to-get-around-browser-connection-limits/comment-page-1#comment-245390 Alex Tue, 19 Dec 2006 17:06:51 +0000 http://ajaxian.com/?p=1944#comment-245390 Of course large sites will work that way - you just have to understand how to load balance the requests. Networking and system architecture 101. Of course large sites will work that way – you just have to understand how to load balance the requests. Networking and system architecture 101.

]]> By: Anonymous Coward http://ajaxian.com/archives/using-cnames-to-get-around-browser-connection-limits/comment-page-1#comment-245389 Anonymous Coward Tue, 19 Dec 2006 16:46:07 +0000 http://ajaxian.com/?p=1944#comment-245389 This is an excellent way to kill your webserver. It may work with 3 or 4 concurrent users, but large sites won't work that way. This is an excellent way to kill your webserver. It may work with 3 or 4 concurrent users, but large sites won’t work that way.

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