Month: April 2008

Enabling the Apache2 – Tomcat5 mod_jk Connector

Often you want to use Apache HTTP for static content, yet use Tomcat for JSP and other Java type work.  This is a very common infrastructure for enterprise applications, particularly when using ‘pools’ of servers for performance, redundancy and security.  

In order to accomplish this, all connections need to be handled by the Apache webserver, which will delegate appropriate requests to Tomcat for it to process.

Here’s a simple setup to get you started:

  • First you need to get the connector appropriate to your installation:

    http://tomcat.apache.org/connectors-doc/

  • Next make sure the connector file is in the /conf folder of your Apache installation.

    NOTE: I prefer to use this path and leave the version name to make maintenance and backups easier.

  • Add the following line to httpd.conf

    LoadModule jk_module conf/mod_jk-1.2.26-httpd-2.2.4.so

  • Now, add the following to http.conf

    <IfModule jk_module>
    Include “c:/TOMCATPATH/conf/auto/mod_jk.conf”
    JkWorkersFile conf/workers.properties
    JkLogFile “c:/LOGSPATH/tomcat55_mod_jk.log”
    </IfModule>

  • Add the c:/APACHEPATH/conf/workers.properties file with the following (minimal) contents:

    worker.list=ajp13
    worker.ajp13.port=8009
    worker.ajp13.host=localhost
    worker.ajp13.type=ajp13

  • Finally, restart both Apache and Tomcat
  • The following file should have been created in c:/TOMCATPATH/conf/auto/mod_jk.conf

    ########## Auto generated on …some datetime… ##########

    <IfModule !mod_jk.c>
      LoadModule jk_module “C:/APACHEPATH/conf/mod_jk-1.2.26-httpd-2.2.4.so”
    </IfModule>

    JkWorkersFile “C:/TOMCATPATH/conf/jk/workers.properties”
    JkLogFile “c:/LOGSPATH/mod_jk.log”

    JkLogLevel emerg

    <VirtualHost localhost>
        ServerName localhost

        JkMount /webdav ajp13
        JkMount /webdav/* ajp13

        JkMount /servlets-examples ajp13
        JkMount /servlets-examples/* ajp13

        JkMount /jsp-examples ajp13
        JkMount /jsp-examples/* ajp13

        JkMount /balancer ajp13
        JkMount /balancer/* ajp13

        JkMount /host-manager ajp13
        JkMount /host-manager/* ajp13

        JkMount /tomcat-docs ajp13
        JkMount /tomcat-docs/* ajp13

        JkMount /manager ajp13
        JkMount /manager/* ajp13
    </VirtualHost>

If all went well, you should be able to access  your Tomcat server webapps on the regular HTTP port used by your Apache installation.

Cheers!

JSON – JavaScript Object Notation

Here’s another simple way to optimize code and network traffic. XML… by it’s very definition is wasteful as it exchanges size for readability. JSON is a different approach that maintains readability as well as reduces the size to a minimum. This method can be used in any client-server environment, not just between a browser and server.

JSON (JavaScript Object Notation) is a lightweight data-interchange format that is easy for humans to and machines to read/parse and write/generate. JSON is a text format that is completely language independent but uses conventions that are familiar to most programmers familiar with OO languages.

JSON is built on two structures:

  • A collection of name/value pairs. In various languages, this is realized as an object, record, struct, dictionary, hash table, keyed list, or associative array.
  • An ordered list of values. In most languages, this is realized as an array, vector, list, or sequence.

Key Concepts:

  • An object is an unordered set of name/value pairs. An object begins with { (left brace) and ends with } (right brace). Each name is followed by : (colon) and the name/value pairs are separated by , (comma).
  • An array is an ordered collection of values. An array begins with [ (left bracket) and ends with ] (right bracket). Values are separated by , (comma).
  • A value can be a string in double quotes, or a number, or true or false or null, or an object or an array. These structures can be nested.
  • A string is a collection of zero or more Unicode characters, wrapped in double quotes, using backslash escapes. A character is represented as a single character string. A string is very much like a C or Java string.
  • A number is very much like a C or Java number, except that the octal and hexadecimal formats are not used.

REFERENCES:

Cheers!

Improving network performance with server side HTTP Compression

I spend a lot of my time tweaking the performance of web applications, in addition to optimizing code it’s also necessary to verify that your server settings are also optimized for network performance to reduce bandwidth usage and thus client response times.

NOTE: This is a tradeoff between CPU and network performance, it works by compressing the content on the server just before it is sent over the wire…. when the client receives it, it then also spends some of it’s resources to decompress the content.

The Apache HTTP server provided mod_deflate (for 2.x) or mod_gzip (for 1.3).

Here’s a quick start as well as a few references:

In httpd.conf:

1. Uncomment the module:

LoadModule deflate_module modules/mod_deflate.so

2. Add the following (modify if required):

<IfModule deflate_module>
#AddOutputFilterByType DEFLATE text/html text/plain text/xml text/css text/javascript
AddOutputFilterByType DEFLATE text/*
AddOutputFilterByType DEFLATE application/xml
AddOutputFilterByType DEFLATE application/xhtml+xml
#AddOutputFilterByType DEFLATE application/x-javascript

<Location />
# Insert filter
SetOutputFilter DEFLATE

# Netscape 4.x has some problems…
BrowserMatch ^Mozilla/4 gzip-only-text/html

# Netscape 4.06-4.08 have some more problems
BrowserMatch ^Mozilla/4\.0[678] no-gzip

# MSIE masquerades as Netscape, but it is fine
# BrowserMatch \bMSIE !no-gzip !gzip-only-text/html

# NOTE: Due to a bug in mod_setenvif up to Apache 2.0.48
# the above regex won’t work. You can use the following
# workaround to get the desired effect:
BrowserMatch \bMSI[E] !no-gzip !gzip-only-text/html

# Don’t compress images or ZIP/GZ/7Z
SetEnvIfNoCase Request_URI \
\.(?:gif|jpe?g|png|zip|7z|gz)$ no-gzip dont-vary

# Make sure proxies don’t deliver the wrong content
Header append Vary User-Agent env=!dont-vary
</Location>
</IfModule>

REFERENCES:

Cheers!

Free Antivirus Software

So, a family member has recently approached me about virus scan products for Windows. It seems that, while he runs a commercial product, it’s a little dated and he does not keep up on the frequent updates, unfortunately this has put him into a position where his computer was infected and has become almost unusable. Using the same commercial products he’s unable to clean up the mess and has already lost many files.

I’ve been a convert to Avast for several years and even run it on my servers to scan for malicious content, it’s both free for non-commercial use and updates automatically.

Other products worth considering:

For Windows:

Unix/Linux:

Mac OS/X:

Cheers!

Writing Popup HTML content with Javascript

Occasionally, there come a time when old tricks become handy on solving new problems. Recently, an application that I support had some serious network latency when attempting to open a popup consisting exclusively of static content. While this small page came from a webserver with appropriate caching headers being sent, it still took upwards of 2 seconds for the page to be displayed by the client browser because of network latency issues. 

True, this was for MSIE, and there are some notorious performance issues with the javascript used for popups, but those are different topics to be discussed later.

Old implementation, loads content of ‘somefile.html’ as a url popup:

<script type=”text/javascript”><!–
function testwindow(){
  var linkWin = window.open(‘/somefile.html’,”,’width=300,height=200,scrollbars=no,toolbar=no’);
}
// –></script>
<a href=”javascript:testwindow();”>TEST</a>

New implementation, creates content of ‘somefile.html’ in javascript instead:

<html>
<head>
<title>Popup Demo</title>
<script type=”text/javascript”>
function testwindow(x) {
  var content;
  var linkWin = window.open(”,”,’width=300,height=200,scrollbars=no,toolbar=no’);
  if (!linkWin.opener) { linkWin.opener = self; }
    content = “<!DOCTYPE html><html><head>”;
    content += “<title>Example</title>”;
    content += ‘</head><body bgcolor=”#ccc”>’;
    content += “<p>Any HTML will work, just make sure to escape \”quotes\”,”;
    content += ‘or use single-quotes instead.</p>’;
    content += “<p>You can even pass parameters… (” + x + “)</p>”;
    content += “</body></html>”;
    linkWin.document.open();
    linkWin.document.write(content);
    linkWin.document.close();
    //return false;
  }
</script>
</head>
<body>
<a href=”javascript:testwindow(‘this is x’);”>TEST</a>
</body>
</html>

NOTE: there is one small performance tradeoff here,  in the ‘new’ case you will always be downloading the content of the popup, even if you never use it.  This can be remediated by adding it to an external static .JS file.
Cheers!

Enerjy plugin for Eclipse IDE

I’ve previously written on the benefits of static analysis of java code with the use of PMD and FindBugs.  I was recently turned on to a new tool that performs similar testing of code within the Eclipse IDE.

When I first found this tool it was free, since that time it’s come out of beta and is now a little costly, but it may still be worth it due to the functionality it provides.

The premise of this tool is a little different than other ones, while it covers much of the same need, it also performs many tests that I would previously use CheckStyle to do.  This only provides them at runtime and in a common manner within the IDE.

REFERENCES:

Cheers! 

Add HTTP Headers in Apache Response

This can be used to for several reasons:

  1. To add headers to modify the behavior of a specific ‘misbehaving’ browser or client.
  2. To replace headers that you don’t want leaked to the Internet.
  3. To add monitoring information to your server responses.

Changes can be accomplished in the Apache2 ‘httpd.conf’ file.

  1. Verify that the module is not disabled or commented out:

    LoadModule headers_module modules/mod_headers.so

  2. To add some common metrics:

    <IfModule headers_module>
    Header append MyHeader “%D %t”
    </IfModule>

  3. To Hide the HTTP Server header that you send in your responses (often done for security through obscurity):
    <IfModule headers_module>
    Header unset Server
    </IfModule>
  4. You could also replace the Server Header like this:

    <IfModule headers_module>
    Header set Server “ScottServer 1.0”
    </IfModule>

Cheers!
REFERENCES:

Configuring Apache webserver for browser caching of web content…

This is a HUGE topic, I’ve outlined some simple steps below as well as my initial configuration for you to start with…

NOTE: this is for simple ‘static’ content such as images, additional work is required for dynamic (program generated) content, such as that generated in PHP.

1. In ‘httpd.conf’ make sure the following line is uncommented.

LoadModule expires_module modules/mod_expires.so

2.  In ‘httpd.conf’ add the following:

ExpiresActive On
### Expire images 1 day from when they’re accessed
ExpiresByType application/java-archive “access plus 1 day”
ExpiresByType image/gif “access plus 1 day”
ExpiresByType image/png “access plus 1 day”
ExpiresByType image/jpg “access plus 1 day”
ExpiresByType image/jpeg “access plus 1 day”
ExpiresByType image/x-icon “access plus 1 day”
ExpiresByType text/css “access plus 1 day”
ExpiresByType text/javascript “access plus 1 day”
ExpiresByType text/xml “access plus 1 day”
ExpiresByType application/xml “access plus 1 day”
ExpiresByType text/plain “access plus 1 month”
 

3. (Optional) Set default expiry of content in ‘httpd.conf’:

### Expire everything else 1 day from when it’s last modified
ExpiresDefault “modified plus 1 day”

NOTE: These we’re my original settings, you may want to add attitional MIME type and expiry configurations particular to your web content.

REFERENCES:

Windows Tools for reading NTFS and Linux partitions

I’ve had to do my share of hard-drive recoveries over the years and have found the tools provided by DiskInternals to be invaluable in several occurances.

I’d previously used their NTFS Reader software to recover files from bad partitions after multi-booting to an older Windows operating system drive on the same machine.

Now I’ve found that they offer an EXT2/EXT3 Reader to allow Windows to access Linux partitions.

This is great for less-technical users that experience fatal errors in their operating systems as there’s now a relatively simple way to access the ‘familiar’ Windows tooling to recover files on the ‘bad’ partition. For the power-user, this affords a means for people making the switch to Linux a means in which to access their files in Windows in the off chance that they have to use software not usable under WINE.

Product Pages:

NOTE: Similar tooling exists to read Mac HPFS partitions, that topic saved for a later post!

Cheers!

WINE Is Not an Emulator

I post a lot about open source applications, WINE is another notable contender as it gives users an option to run many mainstream Window applications on a Linux (even Apple’s OS/X variant) platform by providing access to the Windows API’s to those host operating systems.

http://www.winehq.org/
http://appdb.winehq.org/ – List of applications supported

Ah, for those of you still running IBM’s OS/2 platform, you too can run Win32 applications with Odin:
http://odin.netlabs.org/

Cheers!