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samxli
Asked: 2011-07-16 01:21:18 +0800 CST

web page slow load due to long DNS lookup

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My website currently is running slow when doing certain AJAX calls. If I do the ajax action consecutively in a row, it is fine. But if I pause for a few minutes and then fire off the ajax event, the response would take a long time. The reason, according the the timeline, is DNS Lookup.

I'm currently using a DNS provider but could this also be a problem with my web app itself or Apache?

My app is running on the LAMP stack. This problem happens for different people. So it is probably not a problem with my local machine or browser.

See attached image for the timeline sample. The first post request took a long time but the subsequent ones were all below 1 second.

enter image description here

More Info:

I recently changed my vhost settings for apache using ServerAlias in an entry. Before the ServerAlias had it's own entry as a ServerName.

Before:

NameVirtualHost *:80

<VirtualHost *:80>
  DocumentRoot /home/staging/www
  ServerName mydomain.com
</VirtualHost>

<VirtualHost *:80>
  DocumentRoot /home/staging/www
  ServerName www.mydomain.com
</VirtualHost>

<VirtualHost *:80>
  DocumentRoot /home/staging/www
  ServerName test.mydomain.com
</VirtualHost>

Now:

NameVirtualHost *:80
<VirtualHost *:80>
  DocumentRoot /home/staging/www
  ServerName mydomain.com
  ServerAlias www.mydomain.com test.mydomain.com
</VirtualHost>
domain-name-system php networking apache-2.2 lamp

2 Answers

  1. You might check into the TTL of the remote DNS record(s) to see if "they" are set too "aggressively" versus your exceptions/needs.

    • 1

  2. DNS TTLs, as user48838's answer suggests, is something definitely worth looking at. However, if they're set appropriately, you might want to look at your "DNS provider". I mean, I can setup a couple of DNS servers at the end of a DSL line in lower Krakowskia and hang out a shingle as a DNS provider, but that doesn't mean that it's any good.

    I'm a bit cynical of DNS providers in general; it's not a hard service to provide in-house, and you can get a lot more control over your DNS service if you manage it yourself. There's no doubt that if you need global, low-latency, high-availability service, a good-quality anycasted service could do the job, but by gum they're expensive, and I'm not getting the impression that you're doing the service provision for a large-scale website.

    So, I'd be taking a really close and careful squint at your "DNS provider", and unless you can really convince yourself that they're not the source of the problem, either get a better one, or just bring it in-house, so you can at least manage the quality of service and ensure that it meets some minimum standard.

    • 1