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Shutdown tomcat server node in case of memory depletion – Avoiding Tomcat Out of memory

Friday, June 6th, 2014

Out Of Memory Errors, or OOMEs, are one of the most common problems faced by Apache Tomcat users. Tomcat cluster behind Apache unreachable (causing customer downtimes). OOME errors occur on production servers that are experiencing an unusually high spike of traffic.

Out of memory errors are usually a problem of application and not of Tomcat server. OMEs have become such a persistent topic of discussion in the Apache Tomcat community cause its so difficult to trace to their root cause. Usually 'incorrect' web app code causing Tomcat to run out of memory is usually technically correct.

Most common reasons for Out of Memory errors in application code are:

the heap size being too small
running out of file descriptors
more open threads than the host OS allows
code with high amounts of recursion
code that loads a very large file into memory
code that retaining references to objects or classloaders
a large number of web apps and a small PermGen

The following java option -XX:OnOutOfMemoryError= could be added to any of tomcat java application servers in setenv.sh in JAVA_OPTS= variable in case of regular Out of Memory errors occur making an application unstable.

-XX:OnOutOfMemoryError=<path_to_tomcat_shutdown_script.sh>

Where < path_to tomcat_shutdown_script.sh > is shutdown script(which performs kill <tomcat_pid> if normal shutdown fails) for the tomcat instance.

With this setup if any tomcat instance run out of memory it will be shutdown (shutdown script invoked) – as result the Apache proxy infront of Tomcats should not pass any further requests to this instance and application will visualize / work properly for end customers.

Usually a tomcat_shutdown_script.sh to invoke in case of OOM would initiate a Tomcat server restart something like:

for i in `ps -ef |grep tomcat |grep /my_path_to_my_instance | awk '{print $2}'` do kill -9 "$i" #path and script to start tomcat done

To prevent blank pages returned to customer because of shutdown_script.sh starting stopping Tomcat you can set in Reverse Apache Proxy something like:

<Proxy balancer://mycluster> BalancerMember ajp://10.16.166.48:11010/ route=delivery1 timeout=30 retry=1 BalancerMember ajp://10.16.166.70:11010/ route=delivery2 timeout=30 retry=1 </Proxy>

Where in above example I assume, there are only two tomcat nodes, for more just add respective ones.

Note that if the deployed application along all servers is having some code making it crash all tomcat nodes can get shutdown all time and you can get in a client havoc 🙂

Tags: application, cause, code, common, instance, memory, running, script, server node, servers, shutdown, web
Posted in Everyday Life, System Administration, Various, Web and CMS | 2 Comments »

Screenshot expanded menus on GNOME / KDE in Linux and BSD desktop

Thursday, June 19th, 2014

If you're using actively Linux or FreeBSD on Desktop PC and experimenting with software, taking personal notes, developing software for Linux, writting documentation, participating in free software community etc., you will certainly need use screenshot heavily.

Taking a screenshot in Linux is done in same way as in any modern operating system by using the Print Screen (PrtScr) button, however there are few Nuts & Bolts of Linux screenshotting, to take advantage of full power of screenshot creation (i.e. be able to do some screenshot customization) which are not offered by default screenshot utilities (GNOME – gnome-screenshot and KDE's KSnapshot)

Here are few useful Linux /BSD Screenshot Tips and Tricks:

If you have done screenshots of Linux running programs more than few times already, you have probably noticed the usual way to screenshot by pressing Print Screen (PrtScr) button to take snapshot of the expanded GNOME / KDE menu is not working. In that order of thought you probably wondered whether it is possible to take a screenshot of an expanded menus? As a Linux user, I've been asking myself this question too, and feeling irritated that I cannot prepare screenshot of a GNOME running application expanded menu. I've found two ways (though there are probably many more to make screenshot of an expanded Linux menu). Here is how:

Create screenshot of running application expanded menus

1. Taking screenshot of expanded menu using the command line

As with everything in Linux, there aremultiple ways to make screenshot of expanded Linux menus.

Make timed screenshot of the screen scheduled to screenshot after a set number of seconds.

The quickest way for to screenshot expanded menu is to use gnome-panel-screenshot or ksnapshot from command line. It is interesting pressing Prt Sc kbd button in GNOME invokes gnome-screenshot and in KDE uses ksnapshot

`gnome-panel-screenshot --delay 5`

To not spend time running it from gnome-terminal (in GNOME desktop), press Alt+F2 (simultaneously) and use the Run Application command shortcut.

gnome-panel-screenshot-linux-screenshot-expanded-menus

This will instruct Screenshot utility to wait for 5 seconds before capturing your desktop this should be enough time for you to go to navigate to expanded menu which you want to get screenshotted.

gnome-panel-screenshot-linux-screenshot-expanded-menus1

Make timed screenshot of the screen in GUI with GIMP

(If you're wonderhing what kind of Linux is on screenshot – this is Trisquel – Run Free! GNU / Linux. It is a Spanish distribution focused on providing 100% free software in it – without proprietary firmware or software. Trisquel is based on Debian and uses the dpkg / apt-get package managers. Trisquel is a recommended Linux to use by Richard Stallman and The Free Software Foundation).
To make timed screenshot with GIMP use menus:

`File -> Create -> Screenshot`

linux-screenshot-gimp-create-screenshot-of-expanded-menus-in-gnome-kde-on-linux-bsd

Chosee whether you want to Take screenshot of the entire screen or a Region to Grab and set your wanted Delay

Screenshot will be prepared on $HOME/Desktop, after set time.

Tags: BSD, Gnome, line, Linux, make, menus, running, screenshot, time, use
Posted in Everyday Life, FreeBSD, Linux and FreeBSD Desktop, Various | No Comments »

Allowing MySQL users access from all hosts – Fixing mysql ERROR 1045 (28000): Access denied for user ‘root’@’remote-admin.com’ (using password: YES)

Friday, June 20th, 2014

mysql_allow_access-from-remote-any-host-fix-access-error-after-sql-migration

I recently migrated MySQL database server from host A to host B (remotesystemadministration.com), because I wanted to have the mysql database server on a separate machine (have separation of server running services and have a dedicated mysql server).

MySQL server host (running on localhost previously was set from my mysql config – my.cnf to listen and serve connections on localhost with

bind-address = 127.0.0.1

). MySQL is used by a Tomcat running Java application on localhost and my task was to set the Tomcat to use the MySQL database remotely to MySQL host B (new remote hostname where MySQL is moved is remotesystemadminsitration.com and is running on IP 83.228.93.76).

Migration from MySQL Db server 1 (host A) to MySQL Db server 2 (host B) is done by binary copying the mysql database directory which in this case is (as it is a Debian server installed MySQL), the standard directory where mysql stores its database data is /var/lib/mysql ( datadir = /var/lib/mysql in /etc/mysql/my.cnf)

Binary copying of data from MySQL db (host A) to MySQL Db (host B) is done with rsync

After migrating and trying to login on migrated mysql database on remotesystemadministration.net with mysql cli client:

remotesysadmin:~$ mysql -u root -p

I got following error:

ERROR 1045 (28000): Access denied for user 'root'@'remotesystemadministration.com' (using password: YES)

To fix the issue I had to login remotely from old migration server mysql (host A) cli:

mysql:~$ mysql -u root -p -h remotesystemadministration.com

and run SQL commands:

GRANT ALL PRIVILEGES ON *.* TO 'root'@'remotesystemadministration.com' WITH GRANT OPTION; GRANT USAGE ON *.* TO 'root'@'remotesystemadministration.com' IDENTIFIED BY 'secret-mysql-pass'; FLUSH PRIVILEGES;

Query OK, 0 rows affected (0.03 sec)
Query OK, 0 rows affected (0.00 sec)
Query OK, 0 rows affected (0.00 sec)

Another way to solve the problem is to add the root user to be able to connect from any host (Enable MySQL root access from all host), to do so issue:

GRANT ALL PRIVILEGES ON *.* TO 'root'@'%' IDENTIFIED BY 'password'; FLUSH PRIVILEGES;

Note: In newer version of MySQL, flush privileges could be omitted.

Another approach if you want to substitute access from localhost for all users and enable all users to be able to authenticate to mysql remotely is to execute SQL Query:

UPDATE USER SET host='%' WHERE host='localhost';

Allowing all users to be able to connect from anywhere on the internet is a very bad security practice anyways, if you already have a tight firewall setup and you can only access the server via specific remote IP addresses allowing MySQL access from all hosts / ips should be ok.

Tags: com, config, copying, ERROR, issue, Java, lib, localhost, migration, mysql database, mysql database server, net, remotesystemadministration, root, running, task, var
Posted in MySQL, Programming, System Administration | No Comments »

Run native Internet Explorer 6 on latest Debian / Ubuntu Linux with IEs4Linux

Thursday, July 24th, 2014

Install-internet-explorer-on-debian-linux-IEs4Linux_logo.svg
If you're a GNU / Linux Desktop user like me and you have to administrate hybrid server environments running mixture of MS Windows with Microsoft IIS webserver running active server pages (.ASP) developed application or UNIX / GNU Linux servers web applications using Mono as a server-side language, often you need to have browser which properly supports Internet Explorer Trident web (layout) renderer (also famous as MSHTML).

Having Internet Explorer on your Linux is very useful for web developers who want to test how their website works under IE.

Of course you can always install Windows in Virtualbox VM and do your testing in the Virtual Machine but this takes time to install and also puts a useless load to a PC ….

IES4 Linux is a Linux free (open source) shell script that lets you run Internet Explorer on your Linux desktop.

ies4linux scripts collection uses emulation with WINE (Wine is Not Emulator) emulator to run the native Windows Internet Explorer thus before use it you have to install Wine.

There are plenty of tutorials online about ies4Linux, problem is as it is not updated and developed most tutorials doesn't work on Debian Wheezy / Ubuntu and rest of deb based linux distros.
This is why I decided to write just another ies4linux tutorial that actually works!

On Debian / Ubuntu / Mint Linux install via apt-get:

apt-get –yes install wine

Then with a non-root user download ies4linux-latest.tar.gz. Just in case ies4linux-latest.tar.gz disappears in future I've created also a ies4linux-latest.tar.gz mirror for download here

and unarchive tar archive:

wget http://www.tatanka.com.br/ies4linux/downloads/ies4linux-latest.tar.gz
tar -zxvf ies4linux-latest.tar.gz
cd ies4linux-*
./ies4linux

You will get:

IEs4Linux 2 is developed to be used with recent Wine versions (0.9.x). It seems that you are using an old version. It's recommended that you update your wine to the latest version (Go to: winehq.com).

You need to install cabextract first!
Download it here: http://www.kyz.uklinux.net/cabextract.php

To fulfill this requirement you will need to also cabetract package which is luckily part of Debian:

apt-get install –yes cabextract

On wine version 1.0 and onwards winprefixcreate has been changed to winecfg binary.
To prevent missing wineprefixcreate, errors during ies4linux installer run its necessery to symlink as a workaround:

ln -sv /usr/bin/winecfg /usr/bin/wineprefixcreate

To continue with Internet Explorer ies4Linux installater run again:

./ies4linux

images/internet-explorer-for-linux-debian-gnu-linux-screenshot

/images/internet-explorer-4-linux-installer-debian-gnu-linu-screenshot

You will get the installer GUI window with selection option which Internet Explorer version you want. Choose between IE 5.0, IE 5.5 and IE 6. It is also possible to install IE 7 which is still considered beta version and is less tested and unstable, will probably lead to crashes. If you want to install also IE 7 check it as an option from Advanced menu.

/images/ies4linux-internet-explorer-installer-debian-gnu-linux-screenshot

If you get permission errors after running ies4Linux gui installer to solve that chown recursively directory to the user with which you will be running it:

chown -R hipo:hipo ies4linux-2.99.0.1

Internet Explorer for Linux downloader, will connect Microsoft.com website and download DCOM, MCF and various IE required .CAB files.

If you get some ies4linux GUI installer unexpected crashes you can try to download all required IE binaries, surrounding files and flash player using no-gui installer with cmd:

./ies4linux –no-gui –install-corefonts

IEs4Linux 2 is developed to be used with recent Wine versions (0.9.x). It seems that you are using an old version. It's recommended that you update your wine to the latest version (Go to: winehq.com).

IEs4Linux will:
– Install Internet Explorers: 6.0
– Using IE locale: EN-US
– Install Adobe Flash 9.0
– Install MS Core Fonts
– Install everything at: /home/hipo/.ies4linux
[ OK ]

Downloading everything we need
Downloading from microsoft.com:
   DCOM98.EXE
   mfc42.cab
   249973USA8.exe
   ADVAUTH.CAB
   CRLUPD.CAB
   HHUPD.CAB
   IEDOM.CAB
   IE_EXTRA.CAB
   IE_S1.CAB
   IE_S2.CAB
   IE_S5.CAB
   IE_S4.CAB
   IE_S3.CAB
   IE_S6.CAB
   SETUPW95.CAB
   FONTCORE.CAB
   FONTSUP.CAB
   VGX.CAB
   SCR56EN.CAB

Downloading from macromedia.com:
   100% swflash.cab

Downloading from sourceforge.net
   0%   webdin32.exe[ OK ]bdin32.exe

Installing IE 6
Initializing
Creating Wine Prefix
Your wine does not have wineprefixcreate installed. Maybe you are running an old Wine version. Try to update it to the latest version.

To fix the error:

Your wine does not have wineprefixcreate installed. Maybe you are running an old Wine version. Try to update it to the latest version.

vim lib/functiions.sh

Go to line 36 (Type :36 in vim)

Line:

wine –version 2>&1 | grep -q "0.9." || warning $MSG_WARNING_OLDWINE

Has to be changed to:

wine –version 2>&1 | egrep -q "0.9.|-1." || warning $MSG_WARNING_OLDWINE

Also you need to substitute wineprefixcreate to wineboot (if you haven't already symlinked wineprefixcreate to winecfg – as pointed earlier in article.

To do so make following substitution in lib/install.sh and in lib/functions.sh

cp -rpf lib/install.sh lib/install.sh.bak; cat lib/install.sh |sed -e 's#wineprefixcreate#wineboot#g' > lib/install_new.sh; mv lib/install_new.sh lib/install.sh

cp -rpf lib/install.sh lib/functions.sh.bak; cat lib/functions.sh |sed -e 's#wineprefixcreate#wineboot#g' > lib/functions_new.sh; mv lib/functions_new.sh lib/functions.sh

Also it is necessery to change default corefonts download url which points to sourceforge but is failing. I've made mirror of corefonts files here

cp -rpf lib/install.sh lib/install.sh.bak; cat lib/install.sh |sed -e 's#http://internap.dl.sourceforge.net/sourceforge/corefonts/#www.pc-freak.net/files/corefonts/#g' > lib/install_new.sh; mv lib/install_new.sh lib/install.sh

Re-run the ies4linux console installer:

./ies4linux –no-gui –install-corefonts

….
Es4Linux installations finished!

On installation success you should get output like this
Hopefully you will see no errors like in my case, if you get the corefonts download error again re-run the installer and it should succesully download the files.

To then run ies4linux:

~/bin/ie6

internet-explorer-ies4linx-running-on-debian-gnu-linux-screenshot
Though Ies 4 Linux is good for basic testing it is not psosible to use the browser for normal browsing because its a bit buggy and slow.

By default Internet Explorer 6 behavior is to prompt security alert on various actions, though this might be useful for debugging it is really annoying so I personally disabled those by decreasing from:

Tools -> Internet Options -> Security -> (Security Level)
I've decreased it from Medium to Medium-Low

ies4Linux was not developed since 2008 and as of time of writting ies4linux official project website seems abandoned.

Tags: administrate, application, ASP, browser, CAB, Creating Wine Prefix, Debian Ubuntu Linux, downloads, IEDOM, Internet Explorer Trident, layout, lib, mv, need, running, server, tar archive, web
Posted in Linux, Linux and FreeBSD Desktop, System Administration, Various | No Comments »

Optimize WordPress Pictures with EWWW Image Optimizer, Async JS and CSS and Autoptimize for better Search Engine Ranking

Tuesday, December 9th, 2014

While optimizing picture performance with console tools optipng, jpegoptin, jpegtran, pngcrush (could save you a lot of server space and make pictures downloads faster (and hence increase your website responsiveness and SEO – check out), still for Blogs and WebSites based on WordPress its not worthy to loose time with console acrobatics but simply use EWWW Image Optimizer to Optimize all old or new uploaded Images.

To work EWWW Image Optimizer needs jpegtran, optipng, pngout and gifsicle to be installed on the Linux / BSD server. EWWW Image Optimizer can load the command line tools also from a Cloud, if a cloud service is running on the server. Once installed the plugin does scan all the imported WordPress Media files and can be run to optimize picture files on present blog psot / pages.

EWWW Image Opitimizer plugin does a good job in reducing file size on NextGEN, GRAND FlAGallery galleries.

Here is how EWWW Image Optimizer works taken from plugin's website:
How are JPGs optimized?

Lossless optimization is done with the command jpegtran -copy all -optimize -progressive -outfile optimized-file original-file. Optionally, the -copy switch gets the 'none' parameter if you choose to strip metadata from your JPGs on the options page. Lossy optimization is done using the outstanding JPEGmini utility.
It is better if the server has not the jpegtran, pngout, gifsicle utilities installed as the plugin provides an uptodate static compiled Linux binaries.

How are PNGs optimized?

There are three parts (and all are optional). First, using the command pngquant original-file, then using the commands pngout-static -s2 original-file and optipng -o2 original-file. You can adjust the optimization levels for both tools on the settings page. Optipng is an automated derivative of pngcrush, which is another widely used png optimization utility.

How are GIFs optimized?

Using the command gifsicle -b -O3 –careful original file. This is particularly useful for animated GIFs, and can also streamline your color palette. That said, if your GIF is not animated, you should strongly consider converting it to a PNG. PNG files are almost always smaller, they just don't do animations. The following command would do this for you on a Linux system with imagemagick: convert somefile.gif somefile.png

Some othe plugins that could strenghten your WordPress Search Engine Optimization ranking worthy to check are:

Async JS and CSS

Most importantly plugin solves "Render-blocking JavaScript and CSS" warning shown during site audit with Google Developers PageSpeed Insight. By the way Google PageSpeed Insight is a precious tool so I recommend you check if you already haven't, Google's suggestions could often double or triple daily site visitors

What Async JS and CSS does is:

Converts render-blocking CSS and JS files into NON-render-blocking, improving performance of web page

The plugin makes ALL scripts loaded by other plugins to be loaded in asynchronous. All CSS files will be inserted inline into the document code or moved from the document beginning to the end, just before closing BODY tag (or just where you placed wp_foot() function). There are various methods to do that via plugin configuration page.

Autoptimize

Autoptimize speeds up your website and helps you save bandwidth by aggregating and minimizing JS, CSS and HTML.

What does the plugin do to help speed up site?

It concatenates all scripts and styles, minifies and compresses them, adds expires headers, caches them, and moves styles to the page head, and scripts to the footer. It also minifies the HTML code itself, making your page really lightweight. Autoptimize is very much like WP Mnify (CSS / JS) minifaction WP plugin. The only difference and reason why you might want to use WP Mnify is it does HTML minification – something that WP Minify does not. Both plugins play nice together the only thing to be careful is not to configure CSS / JS minification in both Autoptimize and WP Minifyas this might slower instead of fasten the WP site.

A great bunch of other useful WP plugins to make a WordPress Blog friendly to Search Engines is here.

Tags: async js css, autoptimize wordpress, command line tools, CSS, css js and images optimization, HTML, images, make smaller pictures wp, optimization, optimize css and javascript wp, performance, pictures reduce, plugin, png, running, SEO, server, website, Wordpress, wp, WP JS, www image optimizer
Posted in Everyday Life, System Administration, Various, Web and CMS, Wordpress | 1 Comment »

Disable Bluetooth on CentOS / RHEL (Redhat) / Fedora Linux servers – Disable hidd bluetooth devices

Thursday, January 29th, 2015

Bluetooth protocol on Linux is nice to have (supported) on Linux Desktop systems to allow easy communication wth PDAs, Tablets, Mobiles, Digital Cameras etc, However many newly purchased dedicated servers comes with Bluetooth support enabled which is a service rarely used, thus it is a good strong server security / sysadmin practice to remove the service supporting Blueetooth (Input Devices) on Linux hosts this is the hidd (daemon) service, besides that there are few Linux kernel modules to enable bluetooth support and removing it is also a very recommended practice while configuring new Production servers.

Leaving Blueetooth enabled on Linux just takes up memory space and potentially is a exposing server to possible security risk (might be hacked) remotely.
Thus eearlier I've blogged on how bluetooth is disabled on Debian / Ubuntu Linux servers an optimization tuning (check) I do on every new server I have to configure, since administrating both RPM and Deb Linux distributions I usually also remove bluetooth hidd service support on every CentOS / RHEL / Fedora Linux – redhat (where it is installed), here is how :

1. Disable Bluetooth in CentOS / RHEL Linux

a) First check whether hidd service is running on server:

[root@centos ~]# ps aux |grep -i hid
…

b) Disable bluetooth services

[root@centos ~]# /etc/init.d/hidd stop
[root@centos ~]# chkconfig hidd off
[root@centos ~]# chkconfig bluetooth off
[root@centos ~]# /etc/init.d/bluetooth off

c) Disable any left Bluetooth kernel module (drivers), not to load on next server boot

[root@centos ~]# echo 'alias net-pf-31 off' >> /etc/modprobe.conf

If you don't need or intend to use in future server USBs it is also a good idea to disable USBs as well:

[root@centos ~]# lsmod|grep -i hid
usbhid 33292 0
hid 63257 1 usbhid
usbcore 123122 4 usb_storage,usbhid,ehci_hcd

[root@centos ~]# echo 'usbhid' >> /etc/modprobe.d/blacklist.conf
[root@centos ~]# echo 'hid' >> /etc/modprobe.d/blacklist.conf
[root@centos ~]# echo 'usbcore' >> /etc/modprobe.d/blacklist.conf

2. Disable Bluetooth on Fedora Linux

Execute following:

[hipo@fedora ~]# /usr/bin/sudo systemctl stop bluetooth.service
[hipo@fedora ~]# /usr/bin/sudo systemctl disable bluetooth.service

3. Disable Bluetooth on Gentoo / Slackware and other Linuces

An alternative way to disable bluetooth that should work across all Linux distributions / versions is:

[root@fedora ~]# su -c 'yum install rfkill'
[root@fedora ~]# su -c 'vi /etc/rc.d/rc.local'

Place inside, something like (be careful not to overwrite something, already execution on boot):

#!/bin/sh
rfkill block bluetooth
exit 0

4. Disable any other unnecessery loaded service on boot time

It is a good idea to also a good idea to check out your server running daemons, as thoroughfully as possible and remove any other daemons / kernel modules not being used by server.

To disable all unrequired services, It is useful to get a list of all enabled services, on RedHat based server issue:

[root@cento ~]# chkconfig –list |grep "3:on" |awk '{print $1}'
…

A common list of services you might want to disable if you're configuring (Linux, Apache, MySQL, PHP = LAMP) like server is:

chkconfig anacron off
chkconfig apmd off
chkconfig atd off
chkconfig autofs off
chkconfig cpuspeed off
chkconfig cups off
chkconfig cups-config-daemon off
chkconfig gpm off
chkconfig isdn off
chkconfig netfs off
chkconfig nfslock off
chkconfig openibd off
chkconfig pcmcia off
chkconfig portmap off
chkconfig rawdevices off
chkconfig readahead_early off
chkconfig rpcgssd off
chkconfig rpcidmapd off
chkconfig smartd off
chkconfig xfs off
chkconfig ip6tables off
chkconfig avahi-daemon off
chkconfig firstboot off
chkconfig yum-updatesd off
chkconfig mcstrans off
chkconfig pcscd off
chkconfig bluetooth off
chkconfig hidd off

In most cases you can just run script like this – centos-disable_non-required_essential_services_for_lamp_server.sh.

Another useful check the amount of services each of the running server daemons is using, here is how:

ps aux | awk '{print $4"t"$11}' | sort | uniq -c | awk '{print $2" "$1" "$3}' | sort -nr

Output of memory consumption check command is here

Tags: alternative, check, common, daemons, Disable Bluetooth, echo, fedora linux, good, idea, modprobe, novice, running, server security
Posted in Bluetooth, Computer Security, Linux, Linux and FreeBSD Desktop, Remote System Administration, System Administration, Various | No Comments »

How to configure Apache to serve as load balancer between 2 or more Webservers on Linux / Apache basic cluster

Monday, October 28th, 2013

Apache doing load balancer between Apache servers Apache basic cluster howto

Any admin somehow involved in sphere of UNIX Webhosting knows Apache pretty well. I've personally used Apache for about 10 years now and until now I always used it as a single installation on a Linux. Always so far whenever the requirements for more client connections raised up, web hosting companies I worked for did a migration of Website / websites on a newer better (quicker) server hardware configuration. Everyone knows keeping a site on a single Apache server poses great RISK if the machine hangs up for a reason or gets DoSed this makes websites unavailable until reboot and poses unwanted downtime. Though I know pretty well the concept of load balancing until today I never had configured Apache to serve as Load balancer between two or more identical machines set-upped to interpret PHP / Perl scripts. Amazingly load balancing users web traffic happened to be much easier than I supposed. All necessary is a single Apache configured with mod_proxy_balancer which acts as proxy and ships HTTP requests between two Apache servers. Logically its very important that the entry traffic host with Apache mod_proxy_balancer has to be configured to only run only mod_proxy_balancer otherwise it will be eating unnecessary server memory as with each unnecessary loaded Apache module usage of memory resources raise up.

The scenario of my load balancer and 2 webserver hosts behind it goes like this:

a. Apache with load balancer with external IP address – i.e. (83.228.93.76) with DNS record for ex. www.mybalanced-webserver.com
b. Normally configured Apache to run PHP scripts with internal IP address through NAT – (Network address translation) (on 10.10.10.1) – known under host JEREMIAH
c. Second identical Apache to above host running on 10.10.10.1 with IP 10.10.10.2. with internal host ISSIAH.

N.B.! All 3 hosts are running latest Debian GNU / Linux 7.2 Wheezy

After having this in mind, I proceeded with installing the on 83.228.93.76 apache and removing all unnecessary modules.

!!! Important note is if you use some already existent Apache configured to run PHP or any other unnecessary stuff – make sure you remove this otherwise expect severe performance issues !!!
1. Install Apache webserver

loadbalancer:~# apt-get install --yes apache2
2. Enable mod proxy proxy_balancer and proxy_http
On Debian Linux modules are enabled with a2enmod command;

loadbalancer:~# a2enmod proxy loadbalancer:~# a2enmod proxy_balancer loadbalancer:~# a2enmod proxy_http

Actually what a2enmod command does is to make symbolic links from /etc/apache2/mods-available/{proxy,proxy_balancer,proxy_http} to /etc/apache2/mods-available/{proxy,proxy_balancer,proxy_http}

3. Configure Apache mod proxy to load balance traffic between JEREMIAH and ISSAIAH webservers

loadbalancer:~# vim /etc/apache2/conf.d/proxy_balancer

/etc/apache2/conf.d/proxy-balancer

Paste inside:

<Proxy balancer://mycluster> BalancerMember http://10.0.0.1 BalancerMember http://10.0.0.4 </Proxy> ProxyPass / balancer://mycluster – See more at: http://www.elastichosts.com/support/tutorials/add-a-front-end-apache-cloud-load-balancer/#sthash.29iPnZpz.dpuf

<Proxy balancer://mycluster>
BalancerMember http://10.10.10.1
BalancerMember http://10.10.10.2
</Proxy>
ProxyPass / balancer://mycluster

4. Configure Apache Proxy to access traffic from all hosts (by default it is configured to Deny from all)

loadbalancer:~# vim /etc/apache2/mods-enabled/proxy.conf
Change there Deny from all to Allow from all

Deny from all

/etc/apache2/mods-enabled/proxy.conf

5. Restart Apache

loadbalancer:~# /etc/init.d/apache2 restart

Once again I have to say that above configuration is actually a basic Apache cluster so hosts behind load balancer Apache there should be machines configured to interpret scripts identically. If one Apache server of the cluster dies, the other Apache + PHP host will continue serve and deliver webserver content so no interruption will happen. This is not a round robin type of load balancer. Above configuration will distribute Webserver load requested in ratio 3/4 3 parts will be served by First server and 4th parth will be delivered by 2nd Apache.
Well, that's all load balancer is configured! Now to test it open in browser www.mybalanacer-webserver.com or try to access it by IP in my case: 83.228.93.76

a2enmod proxy

Tags: Apache Proxy, apache server, apache2, com, command, conf, configured, hosts, How to, JEREMIAH, load balancer, load balancing, proxy, running, traffic, webserver, www
Posted in Linux, System Administration, Web and CMS | 1 Comment »

Russian Arcade old school electronic game for your mobile – Russian Eggs (Nu Pogodi)

Thursday, January 30th, 2014

I still remember the days of "Electronic Games". As a citizen of Bulgaria – a country which was almost a Soviet Republic (in alliance with the Soviet Union) and due to existence of separation between Communistic and Democratic societies, we the kids of the Eastern Block didn't have the opportunity to play the so popular in that time in democratic "free world" arcade games on consoles like Nintendo and Atari. Nomatter that in Soviet Union times there were a couple of electronic games. Games were not advanced and were copying already concepts existing in games produced by major game company producers like Konami, Data East, Atari and Nintendo. Russian console like games were a separate game device running its own hardware and software, the major company producing that games was the legendary Electronika.

Elektronika was so emblematic in Soviet Union times that there is probably no kid who used to be a citizen of the USSR who doesn't remember playing some of Elektronika's games. The most famous game produced by the company is "ÐÑƒ ÐŸÐ¾Ð³Ð¾Ð´Ð¸" / Nu Pogodi (Wolf / Vylk) and was popular under emblematic name "Eggs".
the-merry-cook-the-cheerful-cook-veseliy-povar-nintendo-fp-24

The hardware of the Eggs game was actually a clone of famous Nintendo game console – Nintendo EG-26 Eg.
There were a couple of other games which was remake of "The Wolf / Eggs" like "The Merry (Cheerful) Cook" – "Ð’ÐµÑÐµÐ»ÑŒiÐ¹ ÐŸÐ¾Ð²Ð°Ñ€" running on Nintendo FP-24 Chef, Explorers of Space (1989) (running on MG-13) and a couple of others.

MG-13-Explorers-of-Space_1989

So why I bring back this old good memories ? 🙂 Because my readers who remember the Eggs game should know the game has a remake application for Android OS under name Eggs. To install it follow prior link or (Type in Google PlayStore "Eggs" or "Russian Eggs"), install and bring back the mania of the old days of the distant 1989 to 2014!!! 🙂

eggs_electronic-russian-arcade-game

There is no question whoever thought of porting the game for Android was a genious as the size of most middle class mobile smart phones almost perfectly fits the size of the original Nu Pogodi!
The game surely can be a time eater as it is addictive 🙂 The sound effects of the game brings back child memories and are pure joy .
Its nice that the game had a remake asour children can enjoy the same old school arcade game of youth of their fathers 🙂

That's all folks, Enjoy the Wolf 🙂

Tags: citizen, company, couple, Enjoy, game, games, hardware, Nintendo, running, Russian Arcade, Soviet Union
Posted in Entertainment, Everyday Life, Mobile Phone Apps & Games | No Comments »

How to make SSH tunnel with PuTTY terminal client

Monday, November 18th, 2013

Create-how to make ssh tunnel with Putty on microsoft windows Vista / 7 XP / 2000
Earlier I blogged how to create SSH tunnels on Linux. Another interesting thing is how to make SSH tunnels on Windows. This can be done with multiple SSH clients but probably quickest and most standard way is to do create SSH tunnel with Putty. So why would one want to make SSH tunnel to a Windows host? Lets say your remote server has a port filtered to the Internet but available to a local network to which you don't have direct access, the only way to access the port in question then is to create SSH tunnel between your computer and remote machine on some locally binded port (lets say you need to access port 80 on remote host and you will access it through localhost tunneled through 8080). Very common scenario where tunneling comes handy if you have a Tomcat server behind firewalled DMZ| / load balancer or Reverse Proxy. Usually on well secured networks direct access to Tomcat application server will be disabled to its listen port (lets say 11444). Another important great think of SSH tunnels is all information between Remote server and local PC are transferred in strong SSH crypted form so this adds extra security level to your communication.
Once "real life" case of SSH tunnel is whether you have to deploy an application which fails after deployment with no meaningful message but error is returned by Apache Reverse Proxy. To test directly tomcat best thing is to create SSH tunnel between remote host 11444 and local host through 11444 (or any other port of choice). Other useful case would be if you have to access directly via CLI interface an SQL server lets say MySQL (remote port 3306 filtered) and inaccessible with mysql cli or Oracle DB with Db listener on port 1521 (needed to accessed via sqlplus).

In that case Putty's Tunneling capabilities comes handy especially if you don't have a Linux box at hand.
To create new SSH tunnel in putty to MySQL port 3306 on localhost (3306) – be sure MySQL is not running on localhost 😉
Open Putty Navigate in left pane config bar to:

SSH -> Tunnels

Type in

Source Port

– port on which SSH tunnel will be binded on your Windows (localhost / 127.0.0.1) in this example case 3306.

Then for

Destination
– IP address or host of remote host with number of port to which SSH tunnel will be opened.

N.B. ! in order to make tunneling possible you will need to have opened access to SSH port of remote (Destination) host

Once click Open you will be prompted for username on remote host in my case to my local router 83.228.93.76. Once you login to remote host open command prompt and try to connect Windows Command prompt Start -> Run (cmd.exe) ;

C:\Users\\hipo> telnet localhost 3306

Connection should be succesful and you from there on assuming you have the MySQL cli version for windows installed you can use to login to remote SQL via SSH tunnel with;

C:\Users\\hipo> mysql -u root -h localhost -p

To later remove existing SSH Tunnel go again to SSH -> Tunnels press on SSH tunnel and choose Remove

Further you can craete multiple SSH tunnels for all services to remote host where access is needed. Important think to remember when creating multiple SSH connections is source port on localhost to remote machine should be unique

Tags: client, direct access, host, How to, Internet, Linux, localhost, machine, port, Putty, Reverse Proxy, running, say, server, ssh, standard, thing, Windows
Posted in System Administration, Various, Windows | No Comments »

Running System Restore from command prompt on Windows 7 / Fixing broken Windows 7 laptops

Tuesday, November 20th, 2012

doing system restore on windows 7 from command prompt / windows7 systemrestore logo
On Windows, mostly anyone who has a little idea about computing should know of existence of the famous System Restore.

I'm currently fixing a messed up m$ Windows 7 Acer Aspire 7750, laptop whose Desktop icons has disappeared and it seems it is full of Viruses and Spyware.
ACER notebooks does not have the nice feature of IBM / Lenovo notebooks which has a separate Hidden Partition with Windows 7 Install on it, and besides this the Windows 7 with notebook is licensed to the notebook. So simply downloading any cracked version of Win 7 is not an option.

After consulting with a friend I've figured out the only option I have to fix the "barely working" Windows 7 PC is to use Windows System Restore

windows system restore screenshot choose hard drive / Confirm system restore

Usually the traditional way to run System menu is by Navigating to menus:

Start | Programs | Accessories | System Tools | Restore

However as the notebook, I'm fixing is in Dutch as well as it is missing Accessories? Start-up menu, I thought of alternative and did a quick search on how it is possible to run System Restore from command line.

So here is how:

From Windows Command Prompt run command:

%systemroot%\system32\rstrui.exe

Also for me on this Windows 7 Home with Service Pack1, system restore is possible to run by typing in cmd.exe:

rstrui.exe

System Restore choose restore point

Following, few pop-up menus appears which allows choice of the date of last system restore.

I just choose the one made auto few days earlier and proceeded with the System Restore. There is a warning appearing before the system restore warning to make backups before proceeding a step further. Then few clicks a Restart the PC Worked 🙂 It is as quick and easy.

Well of course, though Restoration to a previous working state of the Windows worked like a charm. Still the restored version, was having the usual bunch of Spyware / Malware. So I had to clean up also the Spyware with MalwareBytes and Little Registry Cleaner to solveissues within registry caused by malware.

Tags: command, prompt, restore, running, system, Windows
Posted in Everyday Life, System Administration, Various, Windows | No Comments »

☩ Walking in Light with Christ – Faith, Computing, Diary

Posts Tagged ‘running’

Shutdown tomcat server node in case of memory depletion – Avoiding Tomcat Out of memory

-XX:OnOutOfMemoryError=<path_to_tomcat_shutdown_script.sh>

Allowing MySQL users access from all hosts – Fixing mysql ERROR 1045 (28000): Access denied for user ‘root’@’remote-admin.com’ (using password: YES)

ERROR 1045 (28000): Access denied for user 'root'@'remotesystemadministration.com' (using password: YES)

Optimize WordPress Pictures with EWWW Image Optimizer, Async JS and CSS and Autoptimize for better Search Engine Ranking

Russian Arcade old school electronic game for your mobile – Russian Eggs (Nu Pogodi)

Running System Restore from command prompt on Windows 7 / Fixing broken Windows 7 laptops

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