When in HTTP mode HAProxy’s default health check is a simple OPTIONS request. This has the advantage of being a very lightweight request, and is easy to identify and filter from server logs. Consider this scenario though: HAProxy balances the load between several web servers running nginx and PHP-FastCGI. If nginx is up but PHP-FastCGI goes down, nginx will still properly handle the OPTIONS request from HAProxy, giving the impression that all is well. HAProxy continues sending requests to the ill server which in turn get a 504 Gateway Timeout (or similar) response. Not a very good situation.

A solution would be to use a deeper health check, one that goes beyond nginx to the PHP-FastCGI process. That way if PHP-FastCGI goes down, the whole server is presumed ‘down’.

backend appservers

 mode http

 option httpchk HEAD /health_check.php HTTP/1.1\r\nHost:\ example.com

 server web1 x.x.x.x:80 weight 5 check inter 2000

 server web2 x.x.x.x:80 weight 5 check inter 2000

 server web3 x.x.x.x:80 weight 5 check inter 2000

In the above example I’m using a custom health check request which will be processed by PHP-FastCGI. health_check.php is a lightweight script that contains simply <?php echo "I'm healthy"; ?>. I also added a host header so that the health check will be handled by a specific nginx virtual host. The nginx vhost config has this in it:

location = /health_check.php {

 access_log		off;

 fastcgi_pass	127.0.0.1:9000;

 fastcgi_index	index.php;

 include	/etc/nginx/fastcgi_params;

}

And there you have it–a better HAProxy health check for dynamic websites.

This is just a quick note for anyone who has to deal with Network Solutions hosting (for clients or otherwise). Apperantly Network Solutions doesn’t run PHP with Apache’s mod_php, but rather as a CGI application. That means if you try to put PHP configuration directives in a .htaccess file it will cause a 500 Internal Server Error. My helpful reference: Because Network Solutions Sucks.

You have been warned.

I still need to add support of internationalized TLDs and HTML. So, although it only works with plain text for now, I think it’s off to a good start. Check out the demo or download the source.

You have a news site. You need to display only articles that have been published, and one of the criteria is that they need to have a publish_date before now. Easy, peasy, lemon squeezy.

SELECT author, title, body FROM articles WHERE publish_date <= NOW();

That works, right? Yeeeeah, it works, but it isn’t optimal. The problem is that MySQL can’t use the query cache on any query that has NOW() in it (or CURRENT_TIME() or any of these other functions for that matter). The solution I like to use is have PHP generate the timestamp. Even better is to have PHP round the timestamp, like so:

// Calculate time to nearest 15 minutes
$roundness = 60 * 15;
$rounded_now = (round(time() / $roundness) * $roundness);
$sql = "SELECT author, title, body FROM articles WHERE publish_date <= $rounded_now";

Of course, depending on how time sensitive your application is, you may need to change the code from rounding to 15 minutes to something like 5 minutes, or 1 minute. Hey, even rounding to 30 seconds would be better than using NOW() because you can use query cache!