Weiqi Gao's Observations - apache tag

Tomcat 6.0.18, Apache 2.2.9, proxy_ajp on Ubuntu 8.10: Almost Trivial...

Wed, 24 Dec 2008 02:15:11 GMT

... after four hours of documentation re-reading.

[Update Tue Dec 23 15:30:20 CST 2008] The above line was written two days ago when I moved this blog away from a dying PC. Regular readers might have noticed outages of this blog for stretches of several hours at a time and during the evening hours. The whole machine would lock up while the disk light is a solid on, presumably trying to read something off the disk.

This is the second time a PC has died at home. If you remember, gao-2002 went out of commission only 23 days ago. And now gao-2006 is gone. You've seen gao-2006 mentioned here, here, here, and here.

Luckily, I was able to save all the data from the dying PC before it finally would get a kernel panic during the boot up process. I felt that I was this close to writing a different blog entry that begins: "I'm an idiot and I lost all data in this blog..."

Are your data backed up? Now would be a good time to implement your backup strategy.

With the backed up data, I was able to setup this blog on gao-2009 within four hours, most of it spent on one task. Here's entire process on this Ubuntu 8.10 machine:

Install sun-java6-jdk from Synaptic Package Manager
Install apache2 from Synaptic Package Manager
Install tomcat6 from Synaptic Package Manager
Deploy my blog at /var/lib/tomcat6/webapp/blog
Connecting apache2 to tomcat6

The first four steps are trivial. I did the first three prior to the move. Step 4 took minutes. Step 5 is also trivial, but I didn't know it when I started. What tripped me up is Google. Most of the search results leads to outdated information. And I spent a number of hours following the wrong leads, most of them about mod_jk, which I custom compiled in the early days of this blog.

It finally downed on me that perhaps I should read the documentations. And what a good idea what was. All I need to know is in the documentations:

The gist of the documentation can be distilled to three sentences: Apache 2.2.9 includes mod_proxy_ajp support. Tomcat 6.0.18 is configured with an AJP connector by default. All I need to do is to enable mod_proxy_ajp and then tell it where my webapp is.

To enable mod_proxy_ajp I used the command:

[root@gao-2009] # a2enmod mod_proxy_ajp

To tell Apache 2.2.9 where my webapp is I added /etc/apache2/conf.d/proxy_ajp with the following content:

ProxyPass /blog ajp://localhost:8009/blog
ProxyPassReverse /blog ajp://localhost:8009/blog

<Proxy /blog>
  Order deny,allow
  Allow from all
</Proxy>

It turns out I also need to edit /etc/apache2/mods-enabled/proxy.conf to change a line that says Deny from all into Allow from all. Without this change, noone can access the blog and I get error message that reads:

... client denied by server configuration: proxy:ajp://localhost:8009/...

That's all there is to it.

Thursday Ant Quiz

Thu, 13 Mar 2008 18:27:36 GMT

I'm tearing my hairs out, so I think you should do the same. I'll make you, as a matter of fact, by way of a Thursday Ant quiz:

The Set Up: There are two files in the current directory: Foo.java and Foo.class.

Q: Write an Apache Ant 1.7.0 compatible build.xml file in the directory, which, when invoked with the ant, removes Foo.class but not Foo.java. You cannot use the word "Foo" in the build file.

No Googling, no peeking into the online Ant manual or any Ant books.

Google Flavored Java?

Tue, 13 Nov 2007 18:57:01 GMT

(Via Miguel de Icaza)

Stefano Mazzocchi: Today Google released the Android code and I took a serious look at its internals... and found the solution for the licensing problem. It's called Dalvik and it's the new name of Sun's worst nightmares.

Dalvik is a virtual machine, just like Java's or .NET's.. but it's Google's own and they're making it open source without having to ask permission to anyone (well, for now, in the future expect a shit-load of IP-related lawsuits on this, especially since Sun and Microsoft signed a cross-IP licensing agreement on exactly such virtual machines technologies years ago... but don't forget IBM who has been writing emulation code for mainframes since the beginning of time).

But Android's programs are written in Java, using Java-oriented IDEs (it also comes with an Eclipse plugin)... it just doesn't compile the java code into java bytecode but (ops, Sun didn't see this one coming) into Dalvik bytecode.

So, Android uses the syntax of the Java platform (the Java "language", if you wish, which is enough to make java programmers feel at home and IDEs to support the editing smoothly) and the java SE class library but not the Java bytecode or the Java virtual machine to execute it on the phone (and, note, Android's implementation of the Java SE class library is, indeed, Apache Harmony's!)

I haven't looked inside Android, but I trust Stefano's description. And I believe we are seeing fruits of The Third Fork From Sun that I outlines 215 days ago.

[Update]: Wow. This thing (the emulator) works!

And it advertises itself as "Mozilla/5.0 (Linux; U; Android 0.5; en-us) AppleWebKit/522+ (KHTML, like Gecko) Safari/419.3"