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Apache

Apache load balancer: If a worker doesn't show up....

Since the Apache load balancer seems to be my topic of the week, let's focus on another related question: What happens if a worker (backend server) doesn't show...

Since the Apache load balancer seems to be my topic of the week, let's focus on another related question: What happens if a worker (backend server) doesn't show up for work?Let's say server B needed to go down for maintenance and is no longer available for the cluster:For this example I simply shut server B's Apache daemon down. I made no other changes to my configuration. And voila:# repeat 12 lynx -source http://loadbalancerThis is A.This is C.This is D.This is A.This is...

Apache load balancer: Redirections pwned

HTTP load balancers have one natural enemy: redirections. For example, a "trailing slash" redirect is issued when the server receives a request for a URL...

HTTP load balancers have one natural enemy: redirections. For example, a "trailing slash" redirect is issued when the server receives a request for a URL http://servername/dir where dir is a directory. In such a case the server redirects the browser to http://servername/dirname/ (including the trailing slash):# lynx -mime_header http://loadbalancer/dir | egrep Location:Location: http://serverA/dir/# lynx -mime_header http://loadbalancer/dir | egrep Location:Location:...

Easy HTTP load balancing with Apache

Usually a single AMP system is enough to serve - let's say - around 500 concurrent users. Sometimes more, sometimes less, strongly depending on the particular...

Usually a single AMP system is enough to serve - let's say - around 500 concurrent users. Sometimes more, sometimes less, strongly depending on the particular web application, the overall architecture of your system, of course the hardware itself, and how you define "concurrent users".Nevertheless, if your server gets too slow, you'll need to take actions. You may upgrade your server up to the maximum (aka vertical scaling), optimize your software (aka refactoring), and...

Apache's graceful restart (reprise)

In my last week's blog entryUrban legends: Apache reload(ed) I tried to prove that an Apache reload is quite exactly the same as the restart of an Apache web...

In my last week's blog entryUrban legends: Apache reload(ed) I tried to prove that an Apache reload is quite exactly the same as the restart of an Apache web server.One of my dear readers - yes, at least someone seems to read this blog - pointed out that this is not always true, and a reload sometimes work and sometimes not. In contrast to a restart, which always work like a charm.I strongly assume that's a classic observer effect:In physics, the term observer effect refers...

Urban legends: Apache reload(ed)

What's the difference between reloading and restarting an Apache web server? If you google for this you'll find a lot of (wrong) information which may sum up...

What's the difference between reloading and restarting an Apache web server? If you google for this you'll find a lot of (wrong) information which may sum up like this:A reload just let Apache re-read it's configuration file, without restarting the Apache. But if you need to do bigger changes to the config, like adding or removing modules or virtual hosts, you'll may need to do a real restart. Something like this.If Penn & Teller would care about Apache configuration, they...

Save energy! Stop using CGI!

The day CGI was invented was a great day for the Internet, but a dark day for the history of how-to-do-thinks-right. CGI was great, because it gave us (standard...

The day CGI was invented was a great day for the Internet, but a dark day for the history of how-to-do-thinks-right. CGI was great, because it gave us (standard computer nerds) the ability to easily implement dynamically generated HTML pages - the predecessor of todays web applications. The interface was so ingeniously simple and powerful that everyone could use his favorite programming language for implementing web services. You could use C, Perl, AWK, PostScript or even the...

Hide X-Powered-By: PHP

About two weeks ago I showed a simple way to beautify your URLs and hide the use of PHP as the backend of your web site. Since I got a lot of emails from people...

About two weeks ago I showed a simple way to beautify your URLs and hide the use of PHP as the backend of your web site. Since I got a lot of emails from people indirectly asking me how to also hide the X-Powered-By: PHP header which is still showing up in ones web server's HTTP response.As so much in our beautiful world of IT it's very easy:Open your php.ini in the editor of your trust.Find this line:; Decides whether PHP may expose the fact that it is installed on the...

Easily boost your AMP website combo with mod_rewrite

The ScenarioImagine: You run a popular website using AMP technologies, but your hardware is awfully old and over the years, as your website became more and more...

The ScenarioImagine: You run a popular website using AMP technologies, but your hardware is awfully old and over the years, as your website became more and more popular, it's got slower and slower and slower. Today it runs with a load of 42 and smoke pours out of the TCP ports. And because you're a silly idealistic fool you've no money for a new hardware or to pay a reasonable hosting service. What now?The answer is in the book, the book of caches.The ExampleLet me set up a...

Apache: No listening sockets available, shutting down

One of the advantages of maintaing a popular project like XAMPP is the immense amount of community feedback you get. In other words: your inbox is a daily...

One of the advantages of maintaing a popular project like XAMPP is the immense amount of community feedback you get. In other words: your inbox is a daily challenge. PHP 5.3 incompatibilities are hot topics these days. Here's an Apache related one which hits my inbox on a very regular basis.Variant 1Apache complains about:(98)Address already in use: make_sock: could not bind to address [::]:80no listening sockets available, shutting downUnable to open logsThe "Unable to open...