Posts Tagged ‘default installation’

Improve Apache Load Balancing with mod_cluster – Apaches to Tomcats Application servers Get Better Load Balancing

Thursday, March 31st, 2016

improve-apache-load-balancing-with-mod_cluster-apaches-to-tomcats-application-servers-get-better-load-balancing-mod_cluster-logo


Earlier I've blogged on How to set up Apache to to serve as a Load Balancer for 2, 3, 4  etc. Tomcat / other backend application servers with mod_proxy and mod_proxy_balancer, however though default Apache provided mod_proxy_balancer works fine most of the time, If you want a more precise and sophisticated balancing with better load distribuion you will probably want to install and use mod_cluster instead.

 

So what is Mod_Cluster and why use it instead of Apache proxy_balancer ?
 

Mod_cluster is an innovative Apache module for HTTP load balancing and proxying. It implements a communication channel between the load balancer and back-end nodes to make better load-balancing decisions and redistribute loads more evenly.

Why use mod_cluster instead of a traditional load balancer such as Apache's mod_balancer and mod_proxy or even a high-performance hardware balancer?

Thanks to its unique back-end communication channel, mod_cluster takes into account back-end servers' loads, and thus provides better and more precise load balancing tailored for JBoss and Tomcat servers. Mod_cluster also knows when an application is undeployed, and does not forward requests for its context (URL path) until its redeployment. And mod_cluster is easy to implement, use, and configure, requiring minimal configuration on the front-end Apache server and on the back-end servers.
 


So what is the advantage of mod_cluster vs mod proxy_balancer ?

Well here is few things that turns the scales  in favour for mod_cluster:

 

  •     advertises its presence via multicast so as workers can join without any configuration
     
  •     workers will report their available contexts
     
  •     mod_cluster will create proxies for these contexts automatically
     
  •     if you want to, you can still fine-tune this behaviour, e.g. so as .gif images are served from httpd and not from workers…
     
  •     most importantly: unlike pure mod_proxy or mod_jk, mod_cluster knows exactly how much load there is on each node because nodes are reporting their load back to the balancer via special messages
     
  •     default communication goes over AJP, you can use HTTP and HTTPS

 

1. How to install mod_cluster on Linux ?


You can use mod_cluster either with JBoss or Tomcat back-end servers. We'll install and configure mod_cluster with Tomcat under CentOS; using it with JBoss or on other Linux distributions is a similar process. I'll assume you already have at least one front-end Apache server and a few back-end Tomcat servers installed.

To install mod_cluster, first download the latest mod_cluster httpd binaries. Make sure to select the correct package for your hardware architecture – 32- or 64-bit.
Unpack the archive to create four new Apache module files: mod_advertise.so, mod_manager.so, mod_proxy_cluster.so, and mod_slotmem.so. We won't need mod_advertise.so; it advertises the location of the load balancer through multicast packets, but we will use a static address on each back-end server.

Copy the other three .so files to the default Apache modules directory (/etc/httpd/modules/ for CentOS).
Before loading the new modules in Apache you have to remove the default proxy balancer module (mod_proxy_balancer.so) because it is not compatible with mod_cluster.

Edit the Apache configuration file (/etc/httpd/conf/httpd.conf) and remove the line

 

LoadModule proxy_balancer_module modules/mod_proxy_balancer.so

 


Create a new configuration file and give it a name such as /etc/httpd/conf.d/mod_cluster.conf. Use it to load mod_cluster's modules:

 

 

 

LoadModule slotmem_module modules/mod_slotmem.so
LoadModule manager_module modules/mod_manager.so
LoadModule proxy_cluster_module modules/mod_proxy_cluster.so

In the same file add the rest of the settings you'll need for mod_cluster something like:

And for permissions and Virtualhost section

Listen 192.168.180.150:9999

<virtualhost  192.168.180.150:9999="">

    <directory>
        Order deny,allow
        Allow from all 192.168
    </directory>

    ManagerBalancerName mymodcluster
    EnableMCPMReceive
</virtualhost>

ProxyPass / balancer://mymodcluster/


The above directives create a new virtual host listening on port 9999 on the Apache server you want to use for load balancing, on which the load balancer will receive information from the back-end application servers. In this example, the virtual host is listening on IP address 192.168.204.203, and for security reasons it allows connections only from the 192.168.0.0/16 network.
The directive ManagerBalancerName defines the name of the cluster – mymodcluster in this example. The directive EnableMCPMReceive allows the back-end servers to send updates to the load balancer. The standard ProxyPass and ProxyPassReverse directives instruct Apache to proxy all requests to the mymodcluster balancer.
That's all you need for a minimal configuration of mod_cluster on the Apache load balancer. At next server restart Apache will automatically load the file mod_cluster.conf from the /etc/httpd/conf.d directory. To learn about more options that might be useful in specific scenarios, check mod_cluster's documentation.

While you're changing Apache configuration, you should probably set the log level in Apache to debug when you're getting started with mod_cluster, so that you can trace the communication between the front- and the back-end servers and troubleshoot problems more easily. To do so, edit Apache's configuration file and add the line LogLevel debug, then restart Apache.
 

2. How to set up Tomcat appserver for mod_cluster ?
 

Mod_cluster works with Tomcat version 6, 7 and 8, to set up the Tomcat back ends you have to deploy a few JAR files and make a change in Tomcat's server.xml configuration file.
The necessary JAR files extend Tomcat's default functionality so that it can communicate with the proxy load balancer. You can download the JAR file archive by clicking on "Java bundles" on the mod_cluster download page. It will be saved under the name mod_cluster-parent-1.2.6.Final-bin.tar.gz.

Create a new directory such as /root/java_bundles and extract the files from mod_cluster-parent-1.2.6.Final-bin.tar.gz there. Inside the directory /root/java_bundlesJBossWeb-Tomcat/lib/*.jar you will find all the necessary JAR files for Tomcat, including two Tomcat version-specific JAR files – mod_cluster-container-tomcat6-1.2.6.Final.jar for Tomcat 6 and mod_cluster-container-tomcat7-1.2.6.Final.jar for Tomcat 7. Delete the one that does not correspond to your Tomcat version.

Copy all the files from /root/java_bundlesJBossWeb-Tomcat/lib/ to your Tomcat lib directory – thus if you have installed Tomcat in

/srv/tomcat

run the command:

 

cp -rpf /root/java_bundles/JBossWeb-Tomcat/lib/* /srv/tomcat/lib/.

 

Then edit your Tomcat's server.xml file

/srv/tomcat/conf/server.xml.


After the default listeners add the following line:

 

<listener classname="org.jboss.modcluster.container.catalina.standalone.ModClusterListener" proxylist="192.168.204.203:9999"> </listener>



This instructs Tomcat to send its mod_cluster-related information to IP 192.168.180.150 on TCP port 9999, which is what we set up as Apache's dedicated vhost for mod_cluster.
While that's enough for a basic mod_cluster setup, you should also configure a unique, intuitive JVM route value on each Tomcat instance so that you can easily differentiate the nodes later. To do so, edit the server.xml file and extend the Engine property to contain a jvmRoute, like this:
 

.

 

<engine defaulthost="localhost" jvmroute="node2" name="Catalina"></engine>


Assign a different value, such as node2, to each Tomcat instance. Then restart Tomcat so that these settings take effect.

To confirm that everything is working as expected and that the Tomcat instance connects to the load balancer, grep Tomcat's log for the string "modcluster" (case-insensitive). You should see output similar to:

Mar 29, 2016 10:05:00 AM org.jboss.modcluster.ModClusterService init
INFO: MODCLUSTER000001: Initializing mod_cluster ${project.version}
Mar 29, 2016 10:05:17 AM org.jboss.modcluster.ModClusterService connectionEstablished
INFO: MODCLUSTER000012: Catalina connector will use /192.168.180.150


This shows that mod_cluster has been successfully initialized and that it will use the connector for 192.168.204.204, the configured IP address for the main listener.
Also check Apache's error log. You should see confirmation about the properly working back-end server:

[Tue Mar 29 10:05:00 2013] [debug] proxy_util.c(2026): proxy: ajp: has acquired connection for (192.168.204.204)
[Tue Mar 29 10:05:00 2013] [debug] proxy_util.c(2082): proxy: connecting ajp://192.168.180.150:8009/ to  192.168.180.150:8009
[Tue Mar 29 10:05:00 2013] [debug] proxy_util.c(2209): proxy: connected / to  192.168.180.150:8009
[Tue Mar 29 10:05:00 2013] [debug] mod_proxy_cluster.c(1366): proxy_cluster_try_pingpong: connected to backend
[Tue Mar 29 10:05:00 2013] [debug] mod_proxy_cluster.c(1089): ajp_cping_cpong: Done
[Tue Mar 29 10:05:00 2013] [debug] proxy_util.c(2044): proxy: ajp: has released connection for (192.168.180.150)


This Apache error log shows that an AJP connection with 192.168.204.204 was successfully established and confirms the working state of the node, then shows that the load balancer closed the connection after the successful attempt.

You can start testing by opening in a browser the example servlet SessionExample, which is available in a default installation of Tomcat.
Access this servlet through a browser at the URL http://balancer_address/examples/servlets/servlet/SessionExample. In your browser you should see first a session ID that contains the name of the back-end node that is serving your request – for instance, Session ID: 5D90CB3C0AA05CB5FE13121E4B23E670.node2.

Next, through the servlet's web form, create different session attributes. If you have a properly working load balancer with sticky sessions you should always (that is, until your current browser session expires) access the same node, with the previously created session attributes still available.

To test further to confirm load balancing is in place, at the same time open the same servlet from another browser. You should be redirected to another back-end server where you can conduct a similar session test.
As you can see, mod_cluster is easy to use and configure. Give it a try to address sporadic single-back-end overloads that cause overall application slowdowns.

Tools for finding files containing a string (recursively) in Graphical Enviroments (GNOME, KDE and XFCE) on GNU linux and FreeBSD

Monday, April 9th, 2012

1. Finding files containing a specific string with GNOME GUI tool gnome-search-tool

Default installation of GNOME version 2.x and 3.x is equipped with a tool called gnome-search-tool. The tool is used by default in the GNOME's file explorer program Nautilus. The quickest way to look for a certain text string across all the files located in a directory and show them is with nautilus's – find manager.

Below is a screenshot showing the gnome-search-tool embedded in nautilus Screenshot Search for pass string in GNOME nautilus File browser

Nautilus find uses gnome-search-tool program for its file search. Below is a screenshot showing the gnome-search-tool embedded in nautilus:

The gnome-search-tool can be also invoked through Gnome Run Application with ALT+F2 or directly run from terminal e.g.:

hipo@noah:~$ gnome-search-tool

gnome-search-tool screenshot find files by content recursively Debian GNU / Linux

As you can see in below screenshot, gnome-search-tool has many available filter file search criterias.

gnome-search-tool available options screenshot Debian Linux

You see I wanted to look for my project passwords so typed in pass in Contains the text: field and pressed enter to simply look for this text in all my files in the look in folder RichtooRich
Screenshot 3 files found gnome search tool Linux screenshot

Actually gnome-search-tool offers plenty of more options than one might look for. With it one can easily make a combination of complex search critea (filters) and hence a very versatile Desktop file saerch tool. From testing it I can say it for sure more powerful program than MS Windows default file searching program called Find It – this is the program with the ( "dumb dog holing a magnifier" 🙂

One can use the Add or Remove to Add single or various combination of filter criterias. For the sake of testing it, I've added a number of file search filters as you see in the shot below:

Linux graphical program for recursive file search gnome-search-tool - file search example screenshot

The search critias are not matched and therefore 0 files were found.
In case if you wonder how gnome-search-tool works? It is actually a GUI wrapper to Linux's Linux find command .

I wasn't complete sure if it uses find for the file search, so to check I run a one search and in in console ran:
 

hipo@noah:~$ ps axuwf|grep -i find
hipo 18213 2.0 0.0 25568 1276 ? S 23:55 0:00 find /home/hipo/Richtoorich ( -iname * -o -iname .* ) ! -type p -exec grep -i -I -c test {} ; -mtime -1 ( -size 102400 -o -size +102400 ) -user root ! -iname *bad\-name\-to\-omit* -print

You can see the filters set in gnome-search-tool are passed as command arguments to find.

2. Finding files containing a string recursively in KDE with kfind

For KDE users there is a handy little tool called Kfind. Kfind is less "search customizable" if it is compared to gnome-search-tool but it has advantage that its search options are way more "user friendly" / human readable 🙂

To use the tool to look in all files for explicit string fill in Look in: or browse to set the main directory where it will look for the string.

Screenshot find content in multiple files and folders recursively kfind kde programThen in the second Contents (tab) fill in the Containing Text: with the string to be looked for:

Kfind Recursive file search tool for Linux KDE graphic environment, input text field screenshot

Finally in the Names/Location tab, there are two other helpful search options – Show Hidden Files and Case Sensitive Search

Screenshot find content in multiple files and folders recursively kfind kde gui program

I'll be curious to hear if someone knows some other nice software easy and comprehensive to use for Linux / BSD. If you know a better file searcher for Linux than this kfind or gnome-search-tool please drop a comment.