Why is my Github-hosted site responding with HTTP 302 instead of 200?

Question

I own the domain penkov.id.au. I host a blog using github, with an A record for the subdomain michael.penkov.id.au pointing to the github pages server (204.232.175.78).

bash-3.2$ dig michael.penkov.id.au +nocomments +nocmd +nostats

; <<>> DiG 9.8.3-P1 <<>> michael.penkov.id.au +nocomments +nocmd +nostats
;; global options: +cmd
;michael.penkov.id.au.          IN      A
michael.penkov.id.au.   86400   IN      A       204.232.175.78
penkov.id.au.           14399   IN      NS      ns1.linode.com.
penkov.id.au.           14399   IN      NS      ns5.linode.com.
penkov.id.au.           14399   IN      NS      ns4.linode.com.
penkov.id.au.           14399   IN      NS      ns2.linode.com.
penkov.id.au.           14399   IN      NS      ns3.linode.com.
ns1.linode.com.         62648   IN      A       69.93.127.10
ns1.linode.com.         136520  IN      AAAA    2600:3c00::a
ns2.linode.com.         67499   IN      A       65.19.178.10
ns2.linode.com.         122812  IN      AAAA    2600:3c01::a
ns3.linode.com.         124971  IN      A       75.127.96.10
ns3.linode.com.         133162  IN      AAAA    2600:3c02::a
ns4.linode.com.         96383   IN      A       207.192.70.10
ns4.linode.com.         904     IN      AAAA    2600:3c03::a
ns5.linode.com.         44638   IN      A       109.74.194.10
ns5.linode.com.         56329   IN      AAAA    2a01:7e00::a

Recently (around a month ago, maybe more), I've found that all requests to the subdomain (e.g. http://michael.penkov.id.au/blog/2014/01/02/reinventing-the-wheel.html) are met with a 302 response. This is a problem for sites like facebook.com, which don't bother accessing that URL to provide previews. Github notes that 302 redirects are not errors and should be followed, but Facebook apparently ignores that.

I had a look at the request & response headers using Chrome's debugging tools:

Request:

GET /blog/2014/01/02/reinventing-the-wheel.html HTTP/1.1
Host: michael.penkov.id.au
Connection: keep-alive
Cache-Control: max-age=0
Accept: text/html,application/xhtml+xml,application/xml;q=0.9,image/webp,*/*;q=0.8
User-Agent: Mozilla/5.0 (X11; Linux x86_64) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/31.0.1650.63 Safari/537.36
Accept-Encoding: gzip,deflate,sdch
Accept-Language: en-US,en;q=0.8,ja;q=0.6,ru;q=0.4
Cookie: __utma=146715829.533338776.1383309288.1383487335.1383547294.7; __utmz=146715829.1383309288.1.1.utmcsr=(direct)|utmccn=(direct)|utmcmd=(none); __utma=118121621.1819750941.1383609188.1387026971.1388676605.15; __utmb=118121621.11.10.1388676605; __utmc=118121621; __utmz=118121621.1387026971.14.7.utmcsr=facebook.com|utmccn=(referral)|utmcmd=referral|utmcct=/
If-Modified-Since: Thu, 02 Jan 2014 14:38:15 GMT

Response:

HTTP/1.1 302 Found
Connection: close
Pragma: no-cache
cache-control: no-cache
Location: /blog/2014/01/02/reinventing-the-wheel.html

Finally, a sure way to reproduce this problem is to use the Facebook URL debugging tool. Point it at http://michael.penkov.id.au/blog/2014/01/02/reinventing-the-wheel.html to see the problem.

My questions:

• What is causing the redirect? Is it the A-record?
• Where is the redirect actually to? How can I find this out? How can I fix it?
• Can I get rid of the redirect? In other words, how do I get the server to return 200 instead of 302? Other sites with an identical setup (e.g http://mdswanson.com/blog/2013/11/13/some-tools-i-like.html) respond with 200.

Answer 1

Here's what I heard from github support:

The A record pointing to 204.232.175.78 is what's causing the 302 redirect.

Replacing the A record with a CNAME (pointing to mpenkov.github.com) in my DNS settings fixed the problem.

For reference, here's what my DNS record looks like now:

misha@misha-antec:~$ dig michael.penkov.id.au +nocomments +nocmd +nostats

; <<>> DiG 9.8.1-P1 <<>> michael.penkov.id.au +nocomments +nocmd +nostats
;; global options: +cmd
;michael.penkov.id.au.          IN      A
michael.penkov.id.au.   85536   IN      CNAME   mpenkov.github.com.
mpenkov.github.com.     2736    IN      CNAME   github.map.fastly.net.
github.map.fastly.net.  25      IN      A       103.245.222.133