Thoughts Electrique

I’ve been experiencing some serverdowns at a client who uses 1und1 CentOS 5 Servers. After some investigation I discovered that cronjobs were still running although the server appeared to be down. Checking the syslogs showed me a bunch of failed DHCP requests which remebered me of the fact that 1und1 uses DHCP to configure the server machines. I don’t think this is a good idea so I changed the setup to static IPs.

Since 1und1 puts every server behind a dedicated firewall the setup is not as easy as you think. I’ll document it here because It may be useful for other people and certainly for myself after a couple of months.

Configure a static IP address

Open the file /etc/sysconfig/network-scripts/ifcfg-eth0 and edit it to look like the following:

DEVICE=eth0
BOOTPROTO=none
TYPE=Ethernet
ONBOOT=yes
HWADDR=$YOURMACADDRESS
NETMASK=255.255.255.255
IPADDR=$YOURIP
GATEWAY=10.255.255.1

Save the file.

Configure static routes

This is the tricky part. Configuring a default gateway using the GATEWAY= setting is not enough. You have to setup the routes yourself. To do so create a new file /etc/sysconfig/network-scripts/route-eth0 with the following contents:

10.255.255.1 dev eth0
default via 10.255.255.1 dev eth0

Now you only have to reload the networking configuration via

service network reload

and you are done!

This post helped me a lot with the solution.

My OpenCms Apache Integration Howto for OpenCms 6 still get’s a lot of visitors. Many things have changed since I first wrote this howto and certainly things are a lot easier now. I always wanted to rewrite the howto but till then I will just publish a short update on how to integrate OpenCms 7 with Apache and to remove the /opencms prefix with the most recent software.

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As you may remember from my last blogpost I’m currently setting up a new hosting Server. Since this server will also host some OpenCms and JEE sites I need to set up a Servlet Container. In almost all of my projects until today Tomcat was successfully used for this purpose. Be it stand alone or embedded in a JEE application server (e.g. JBoss).

I must admit that I always had some kind of a love-hate relationship with Tomcat. The classloader had some bad issues when reloading a webapplication too often and often killed the complete server. Taking down all of the other webapplications too. Although this has gotten a lot better recently it’s still bothering me a bit.

Since I had some time after my last project I started investigating other open source alternatives. I often heard of Jetty, praised for it’s speed and simplicity, it seemed like a great alternative and I played around with it a bit. I really liked it since it was simple to use and easy to deploy but as I started to google for things like performance measurements or how to use it with a security manager I didn’t really found a lot of documentation (compared to Tomcat) and the performance doesn’t really doesn’t seem to differ from Tomcats.

So I’m once again going the Tomcat route. It has a big community and is even used in military and government organizations. It’s really not a technology decision (although I think Tomcat is solid) but more political thinking.

It will also save me some time which I can invest in trying out other technologies. Meow…

Since I’m currently setting up a new server for hosting purposes I want to share some of my favourite sysadmin tools and practices.

The first featured tool is the shoreline firewall or shorewall. You can find the project at: http://www.shorewall.net/

Shorewall basically is a set of nice configuration files for iptables. Another benefit of shorewall is that it has no runtime part. You just fire up the tool, it configures your iptables and quits. This reduces the load and increases security. Additionally to the technical features there is one thing that makes shorewall really stand out: It has extensive, well-written and understandable documentation. You rarely find a use-case which is not already described in the documentation.

Read on to find out how to set up shorewall in minutes.

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It’s often the case that you need icons and graphics for your own applications, but there is no real style guide available and the customer just wants something decent and coherent. I recently started using the jQuery UI wizard to create the look and feel for my entire application. So far I am very pleased with the results.

You can even create the CSS and images using a wizard: http://jqueryui.com/themeroller

The resulting themes are dual licensed under the GPL and MIT license.

To create good documentation is an art for itself and most often underestimated by us fellow software developers, architects and software project management folks. I won’t go into the detail of what makes a good documentation (in my point of view) in this blog post too deeply (maybe in the future, if you are interested?). Instead I want to point out a negative point which I run into quite frequently: The almighty project document.

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Because someone asked on the mailing list and I keep forgetting the respective API calls to manipulate an OpenCms XMLContent programatically.

This is just a raw code dump not a step by step tutorial.

You can also download a ZIP file for importing it into OpenCms. But you have to adjust the paths manually.

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Since version 7 OpenCms is a Servlet 2.4 and JSP 2.0 conforming application. In addition to the improved expression language (EL) JSP 2.0 also brings in the possibility of developing custom tags(actions) using JSP rather than writing Java code. This allows for some pretty neat things and enables you to go one step further towards cleaner view code. I’ve used this in one of my last projects extensively to refactor common code like pagers and link generation. For example:

<cms:include file="/system/modules/com.example.ocms.commons/elements/pager">
  <cms:param name="currentPage">
    <c:out value="${model.currentPage}"/>
  </cms:param>
  <cms:param name="pageCount">
    <c:out value="${model.pageCount}"/>
  </cms:param>
</cms:include>

Became:

<wt:pager model="${model}"/>

Not does it only look cleaner and is much more focused, it also decouples your view more from the underlying CMS solution. Of course you could also develop a custom tag library using Java (which I have done a few times) but using a JSP the advantage that code can be changed on the fly and even from a web designer. You can always refactor your JSP taglib into a Java one if you need to do it. There are some limitations of JSP tag files (like you can’t use scriptlets in the body) but they are easy to get around.

But as always: This is no silver bullet. There are problems with tag files which may not be obvious at the first glance.

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I recently discovered the freshly released RSS4JSP tag library. Its a wrapper around the mature and widely used Rome RSS library which was developed by Sun and then open sourced. The library allows you to simply display (news) feeds inside your JSP pages.

While it’s certainly a young project, I found it very useful and easy to use. I gave it a try to create the Latest blog posts box on my, OpenCms based, homepage. The box was created during 5 minutes which I think is impressive (given that you have to type the HTML too).

Unfortunately the project does not allow the syndication of multiple feeds into one feed (This is a nice feature of Rome which I used in a recent project) but maybe it will be added in the future (or I will add it myself).

Check it out at sourceforge or visit the authors blog.

I recently had to restart a Java webapplication because somehow the JDBC connection to the database server was hanging completely. This reminded me of a sentence a friend of mine told me during the OpenCms Days 2008.

“Enterprise software just means that it’s targeted at customers who can afford the guy who restarts the application server every few hours.”

I had to laugh because while the quote is clearly cynical it has a true core. Especially if you compare languages like Java and PHP it’s true that PHP doesn’t have these kind problems. This is mostly because of the throw-away-the-state nature of PHP. After every served request PHP forgets what it’s done before and has to completely rebuild the working environment at the next request. Java in contrast is able to remember things between requests. Which makes it more powerful but also harder to maintain (more state, more problems). I’m really not sure if I’m buying into this enterprise-thing anymore. Especially if you need scalability you definitely want to keep application state at a minimum and without state you don’t really need those big interconnected clusters of application servers any more.

Here is a nice talk about scalability and serious (speak enterprise) languages I found recently. It’s from Cal Henderson a software development guy at Flickr. It’s really worth watching. Even if you’re not into Python and Django.

(Watch it at: http://www.youtube.com/watch?v=i6Fr65PFqfk&feature=PlayList&p=D415FAF806EC47A1&index=10)