Quick how to for finding out the list of processes, including threads spawned by these processes
[code] ps -eLf | grep USERNAME [/code]
Explanation of the options
- e : Select all processes
- L : Show threads
- f : Extra full format
Using Apache mod_rewrite for enhancing your application security
For my own notes.. very nice post on perishablepress.com regarding using the different capabilities of mod_rewrite to secure your website (application)
http://perishablepress.com/eight-ways-to-blacklist-with-apaches-mod_rewrite/
Thank you Mr.Tramiel, for introducing me to the world of computers..
When I was ~9 years old, my dad bought home a Commodore 64K. It was slow.. it was terrible graphics and it took for ever to load a program using it’s “tape” drive. But boy was it fascinating to load up basic and write your own programs!!. I can’t say how many summer hours were spent staring at the screen and trying to get things to work.
Looking back, I can say that I probably wouldn’t have been in the technology field, if not for that first taste of computing.
Thank you Mr.Tramiel. RIP.
HOW TO : Redirect web traffic based on URL patterns in Apache
Apache configuration to redirect traffic to a particular URL based on the pattern in the URL (AKA URI). In this particular example, I want to redirect any traffic that does not have the URL starting with /application or /content to redirect to https://domain_name/application
- Enable the rewrite module in Apache
- Add the following conditions in the conf file[code]RewriteCond %{REQUEST_URI} !^/(application|content) [NC]
RewriteRule ^/(.*) https://%{HTTP_HOST}/application [R,L]
[/code]
Explanation of the rule
- ! implies match if the string is not found
- ^ implies start of string
- | implies OR
- [NC] implies not case sensitive (no case)
- The rule will be triggered if the conditions match
- [R,L] means external (client side) redirection and last rule to process
The race is on..
Instead of posting individual posts every day to track my progress (or lack of) in the 60 day challenge, I created this page (https://kudithipudi.org/2012-60-day-resolution/) for the daily entries..
Wish me luck :).
Viva la resistance
I have a confession to make.. I like Big Macs and Krispy Kreme Donuts :). And they have contributed heavily to the increase in my .. hmm.. how do I say this.. mid section :). Plus, it doesn’t help that there is a Krispy Kreme factory and a McDonald’s right on my way to work. And add on to the fact that I haven’t been running for the last year or so, I am proud to say that I have joined the >65% of Americans that are obese.
On my way to work yesterday, I was thinking about what shape (physically) I would be in when Virat grows up. I am sure he doesn’t want to have a dad that can’t play some hoops with him :).
So here’s my 2 month resolution. I am starting with a couple of months because there is a good chance that it might become a habit and then go from there :).
- Exercise for 30 minutes a day (7 days a week)
- Eat dessert only once a week
- No krispy kreme
- No Big Mac
- No fries
- No pop
For every pledge I break, I am going to leave work at 5:00 PM for a week. Believe me when I say that is a tough punishment :). You see.. I love what I do :).
Viva La Resistance!!!
HOW TO : Log all commands issued in shell to syslog
Inspired from this blog post by Vaidas Jablonskis. This tip has been tested on Redhat and Centos distributions.
If you ever wanted to log all the commands issued by users on a server, you can edit the default profile configuration to enable this
- Edit /etc/bashrc file and add the following at the end of the file[code]PROMPT_COMMAND=’history -a >(logger -t "$USER[$$] $SSH_CONNECTION")’ [/code]
- Log out and log back into your session
- Now all your commands are logged in the default log file (/var/log/messages)
HOW TO : Configure Jboss to send log messages to syslog
Jboss uses the log4j framework for providing logging services. log4j is a very flexible framework and can do a lot of things. One of the features provided by log4j is to send log messages to multiple destinations. Here is a quick how to on configuring Jboss to send log messages using the syslog protocol to a syslog server. This is pretty useful, when you are trying to consolidate logs from multiple sources into a central location.
First, some background about how log4j is configured in Jboss
The log4j configuration in Jboss is managed by the file jboss-log4j.xml located at $JBOSS_HOME/server/$JBOSS_PROFILE/conf.
There are three parts to this configuration file
- Appenders
- An appender is a way to define a particular logging method. By default, Jboss provides a bunch of appenders in this config file, but only the FILE and CONSOLE appenders are enabled. The FILE appender writes the log messages to a log file and rotates them based on the criteria in the appender. The CONSOLE appender just sends messages to the console. This will come into picture, when you are not running Jboss as a service. In addition, there are appenders for syslog, snmp, email that are commented out.
- Categories
- A category is where you define the class you want to log messages for and which appender it should use. If you don’t specify an appender or the threshold for the logging level, logging for this class will be done at the default log levels and by the appender specified by the default (root) category.
- Default (root) Category
- As mentioned above, this is the catch all for classes that are not specified specifically in the categories section.
So pictorially, it would look like this 
Getting back to the reason for this post, here is how you would enable the syslog appender and then configure a category to use this appender. For this example, we will use a class names org.kudithipudi
- Enable the syslog appender by un-commenting the following section in the jboss-log4j.xml file[code] <!– Syslog events –>
<appender name="SYSLOG">
<errorHandler/>
<param name="Threshold" value="ERROR"/>
<param name="Facility" value="LOCAL7"/>
<param name="FacilityPrinting" value="true"/>
<param name="SyslogHost" value="localhost"/>
<layout>
<param name="ConversionPattern" value="[%d{ABSOLUTE},%c{1}] %m%n"/>
</layout>
</appender>
[/code] - Add a new category to use this appender [code] <category name="org.kudithipudi">
<priority value="INFO" />
<appender-ref ref="SYSLOG"/>
</category> [/code] - Restart Jboss and you should see messages from Jboss being sent to the syslog server
Couple of notes..
- Even though we are specifying the threshold of INFO in the category, because we specified a threshold of ERROR in the appender, only message of ERROR type will be sent to the syslog server. This is actually pretty useful when you want to specify two appenders to a category and log them at different levels. You can set another appender to INFO level and add it to this category. And in essence, the appender will log everything of INFO and higher, while the syslog appender will only process ERROR messages.
- The destination for the syslog messages is the SysLogHost parameter. In this example, I just used localhost.
Never assume.
When troubleshooting performance issues..never take anything for granted..yes, even if something was not touched or restarted, chances are something touching it has been and might have affected it.
This goes esp for the network (IP and fiber) which don’t change as often as the rest of the environment.
Project Uptime : Progress Report 5 : Getting ready for Reddit and Hacker News
A very timely post on Hacker News by Ewan Leith about configuring a low end server to take ~11million hits/per month gave me some more ideas on optimizing the performance of this website. Ewan used a combination of nginx and varnish to get the server to respond to such traffic.
From my earlier post, you might recall, that I planned on checking out nginx as the web server, but then ended up using Apache. My earlier stack looked like this 
Based on the recommendations from Ewan’s article, I decided to add Varnish to the picture. So here is how the stack looks currently
And boy, did the performance improve or what. Here are some before and after performance charts based on a test run from blitz.io. The test lasted for 60 seconds and was for 250 simultaneous connections.
BEFORE
- Screenshot of Response times and hit rates. Note that the server essentially stopped responding 25 minutes into the test.
- Screenshot of the analysis summary. 84% error rate!!
AFTER
- Screenshot of response times and hit rates
- Screenshot of summary of Analysis. 99.98% success rate!!
What a difference!!.. The server in fact stopped responding after the first test and had to be hard rebooted. So how did I achieve it? By mostly copying the ideas from Ewan :). The final configuration for serving the web pages looks like this on the server end
Varnish (listens on TCP 80) –> Apache (listens on TCP 8080)
NOTE : All the configuration guides (as with the previous entries of the posts in this series) are specific to Ubuntu.
- Configure Apache to listen on port 8080
- Stop Apache [code] sudo service apache2 stop [/code]
- Edit the following files to change the default port from 80 to 8080
- /etc/apache2/ports.conf
- Change [code]NameVirtualHost *:80
Listen 80
[/code] - to [code]NameVirtualHost *:8080
Listen 8080
[/code] - /etc/apache2/sites-available/default.conf (NOTE: This is the default sample site that comes with the package. You can create a new one for your site. If you do so, you need to edit your site specific conf file)
- Change [code] <VirtualHost *:80> [/code]
- To [code]<VirtualHost *:8080> [/code]
- Restart apache and ensure that it is listening on port 8080 by using this trick.
- Install Varnish and configure it to listen on port 80
- Add the Varnish repository to the system and install the package[code]sudo curl http://repo.varnish-cache.org/debian/GPG-key.txt | apt-key add –
sudo echo "deb http://repo.varnish-cache.org/ubuntu/ lucid varnish-3.0" >> /etc/apt/sources.list
sudo apt-get update
sudo apt-get install varnish
[/code] - Configure Varnish to listen on port 80 and use 64Mb of RAM for caching. (NOTE: Varnish uses port 8080 to get to the backend, in this case Apache, by default. So there is no need to configure it specifically).
- Edit the file /etc/default/varnish
- Change [code]DAEMON_OPTS="-a :6081 \
-T localhost:6082 \
-f /etc/varnish/default.vcl \
-S /etc/varnish/secret \
-s malloc,256m"
[/code] - To [code] DAEMON_OPTS="-a :80 \
-T localhost:6082 \
-f /etc/varnish/default.vcl \
-S /etc/varnish/secret \
-s malloc,64m"
[/code] - Restart Varnish [code]sudo service varnish restart[/code]
and you are ready to rock and roll.
There are some issues with this setup in terms of logging. Unlike your typical web server logs, where every request is logged, I noticed that not all the requests were being logged. I guess, that is because varnish is serving the content from cache. I have to figure out how to get that working. But that is for another post :).