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We're trying to figure out if a certain type of web server architecture is better than our current web server. We need to A/B test these 2 boxes with live traffic to really get a sense of which one performs better on our internal KPIs. The hosts involved can't help with the A/B test. So naturally I'm looking to see if it's possible to roughly split the traffic 50:50 between the servers using PHP redirects and sub domains. For example:

  • www.mydomain.com - (randomly redirects all requests to 1 of the following sub domains, maintaining url structure and query strings...)
    • www1.mydomain.com (original webserver config)
    • www2.mydomain.com (new webserver config)

We would need to run this test for at least a week or two to generate good stats. What I'm not sure about is whether the search engines would see this as bad and effect our rankings.

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If the content and internal link structure is different between both servers (I am not talking about the presentation), bots will notice the changes and will likely increase their visits to your site.

They will be very confused if they are being served different content back and forth and this may trigger a manual review. Google wants to be sure about the content being served to users. If algorithms have doubts, they tend to remove sites from search results automatically too.

To avoid such issues, make sure that a given user is always served content from the same server, by setting a cookie for example. Keep in mind Google bots don't use cookies, but you can detect them and send them to the original config server.

If you do that, you will be SEO safe.

  • So the page visible content will be 100% the same as we only want to test server hardware in our A/B test. The only difference in the page source will be that www1 will have different Pingdom RUM code to www2. Other than that the pages should be exact copies. The most significant change, in my mind, is the URL structure. – jnthnclrk May 16 '15 at 9:37
  • If you change the URL structure, then this will be considered as a site structure change. Google indexes pages per their URL. It is a big change. Google will consider your content as duplicate content. It will not penalize you, but you may lose some rankings because of competition between your pages. You should set canonical links to avoid this issue. – Jérôme Verstrynge May 16 '15 at 10:11
  • So keep <link rel="canonical" href="example.com" /> focused on www.? – jnthnclrk May 16 '15 at 15:54
  • If the new webserver has different URLs than original urls on the old server, then the pages served with the new URL should have a canonical link containing the original url. So page www2.example.com/newstructure/mypage.html should have a canonical link with www.example.com/oldstructure/mypage.html. – Jérôme Verstrynge May 16 '15 at 16:18
  • You should not have www.example.com/oldstructure/mypage.html redirected to www1.example.com/oldstructure/mypage.html and having a canonical pointing at www.example.com/oldstructure/mypage.html, because that is a loop Google won't like. It will create a mess. – Jérôme Verstrynge May 16 '15 at 16:25
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A/B testing via PHP will not break your SEO as long as you aren't using any kind of SEO hacking "tricks".

Webpages around the web have all kind of different PHP scripts and companies like Google are pretty good at figuring out what is going on.

Webpage A: Has structured information and links.

Webpage B: Has (generally) the same structured information and links.

To indexing companies these two pages are the same but to your user one might be better(finding information, commenting, retention, etc) and finding out which (A or B) is the point.

Just keep an eye on your analytics platform and tag, comment, or mark any strange dips.

  • No tricks. Just want to test server hardware. Content will be identical (other than some JS tracking code differences). So you don't think the URL changes will cause problems? www & www1 and www2? – jnthnclrk May 16 '15 at 9:40
  • @jnthnclrk Google's algorithm and others do not care about the www1 and www2. As long as your not redirecting to a known spam site or something really strange or out of the ordinary your sites SEO will be fine. The same kind of thing is used for website load balancing where different nodes are named www1-www20 and the loaded balancer redirects users to an under utilized node or a node at random. The key is having the same information on each node. – T. Thomas May 16 '15 at 13:19
  • Sounds great. The only problem is @JVerstry in another answer seems to disagree with you. – jnthnclrk May 16 '15 at 15:53
  • @jnthnclrk what part of our answers disagree? I'd be happy to clarify. – T. Thomas May 16 '15 at 16:50
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    There are situations where Google will automatically consider a domain name and a subdomain as one entity, but you should not rely on this, because your initial plan is to redirect to subdomains only. – Jérôme Verstrynge May 17 '15 at 7:14
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You can consider to use .htaccess to redirect Googlebot always to www., and keep canonical urls to the www. version.

Redirect people with 302 redirections, obviously.

If it's not a good solution, maybe there's another road: you can consider to not redirect all your traffic to ww1. or ww2. Keep 34% of your visitors on www., then split the rest to ww1 and ww2 for 33% each.

You need more time to achieve statistical significance, but in that way you can keep a good amount of traffic on default and it would be more like an A/A/B test.

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