Configurations (Linux)

MySQL Master-Master Replication with Heartbeat

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Setting Up The Two Base Systems

In this setup there will be one master server (which runs the ISPConfig control panel interface) and one slave server which mirrors the web (apache), email (postfix and dovecot) and database (MySQL) services of the master server.

To install the clustered setup, we need two servers with a Debian 6.0 minimal install.

Install only steps 1 – 8 of the perfect server tutorial and not the other steps as they differ for a clustered setup!

In my example I use the following hostnames and IP addresses for the two servers:

Master Server

Hostname: server1.example.tld
IP-address: 192.168.0.105

Slave server

Hostname: server2.example.tld
IP-address: 192.168.0.106

Whereever these hostnames or IP addresses occur in the next installation steps you will have to change them to match the IP's and hostnames of your servers.

It is a good idea to synchronize the system clock with an NTP (network time protocol) server over the Internet. Simply run

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Install Varnish on CentOS/RedHat/SL 5 or 6

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Varnish Cache is a web application accelerator also known as a caching HTTP reverse proxy. It is installed in front of the web application and it speeds up the web application significantly.

Since varnish is not available in CentOS repo, you have to add the EPEL repo. However Varnish suggests you to add its own repo to always get the latest version.

rpm –nosignature -i http://repo.varnish-cache.org/redhat/varnish-3.0/el5/noarch/varnish-release-3.0-1.noarch.rpm

The –no-signature is only needed on initial installation, since the Varnish GPG key is not yet in the yum keyring

Now lets install varnish

# yum install varnish

Make sure it can handle server reboots 🙂

# chkconfig varnish on

Lets change some parameters to suit our enviornment.

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Configuring A High Availability Cluster (Heartbeat) On CentOS

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This guide shows how you can set up a two node, high-availability HTTP cluster with heartbeat on CentOS. Both nodes use the Apache web server to serve the same content.

Pre-Configuration Requirements

Assign hostname node01 to primary node with IP address 172.16.4.80 to eth0.
Assign hostname node02 to slave node with IP address 172.16.4.81.

Note: on node01

uname -n

must return node01.

On node02

uname -n

must return node02.

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Suse Repository for CAS

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Adding up OSS repository for CAS med and app server-

Oss

The main repository, open source software only.

Version: 12.2http://download.opensuse.org/distribution/12.2/repo/oss/

Version: 12.1http://download.opensuse.org/distribution/12.1/repo/oss/

Version: 11.4http://download.opensuse.org/distribution/11.4/repo/oss/

Version: 11.3http://download.opensuse.org/distribution/11.3/repo/oss/

Version: 11.2http://download.opensuse.org/distribution/11.2/repo/oss/

Version: 11.1http://download.opensuse.org/distribution/11.1/repo/oss/

Version: 11.0http://download.opensuse.org/distribution/11.0/repo/oss/

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Install Webmin on Debian Linux

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If you are using the DEB version of webmin, first download the file from the downloads page , or run the command :wget http://prdownloads.sourceforge.net/webadmin/webmin_1.610_all.debthen run the command :

dpkg --install webmin_1.610_all.deb

The install will be done automatically to /usr/share/webmin, the administration username set toroot and the password to your current root password. You should now be able to login to Webmin at the URL http://localhost:10000/. Or if accessing it remotely, replace localhost with your system's IP address.

If Debian complains about missing dependencies, you can install them with the command :

apt-get install perl libnet-ssleay-perl openssl libauthen-pam-perl libpam-runtime libio-pty-perl apt-show-versions pythonIf

you are installing on Ubuntu and the apt-get command reports that some of the packages cannot be found, edit /etc/apt/sources.list and make sure the lines ending with universe are not commented out.

Some Debian-based distributions (Ubuntu in particular) don't allow logins by the root user by default. However, the user created at system installation time can use sudo to switch to root. Webmin will allow any user who has this sudo capability to login with full root privileges.

If you want to connect from a remote server and your system has a firewall installed, see this page for instructions on how to open up port 10000.

Src: http://www.webmin.com/deb.html

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Using FastCGI with Nginx for Performance on a VM

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This weekend I decided to play around with the configuration on my Rackspace Cloud Server. Since our various websites have been doing well lately, the relatively low-powered machine I am running on is starting to fill up its available RAM. So far so good but as everyone quickly learns – running out of memory and hitting the swap space is a performance killer. Since I want my sites to continue to do well, I decided to take action before they hit the RAM limit and start swapping to disk.

This is the old architecture I had deployed. Apache – the Internet’s workhorse – to perform all of the PHP processing, with Nginx as a reverse proxy, passing dynamic (PHP) requests to Apache but serving static files directly to give Apache a break and cut down its footprint.

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PHP accelerator

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Even though compilation is very fast, it still has a resource and time cost, especially on high-traffic servers. We can improve our response times by more than 5x by pre-caching our compiled opcode for direct execution later. There are a few PHP accelerators which accomplish this for us:

Xcache
Xcache is my favourite and is the one I use in my own configurations. It works by caching the compiled PHP opcode in memory so PHP can be directly executed by the web server without expensive disk reads and processing time. Many caching schemes also use Xcache to store the results of PHP rendering so individual pages don’t need to be re-processed.

APC (Alternative PHP Cache)
APC is a very similar product to XCache – in fact XCache was released partially as a response to the perceived lag APC’s support for newer PHP versions. APC is essentially the standard PHP Accelerator – in fact, it will be included by default in PHP 6. As much as I like XCache, it will be hard to compete with built-in caching.

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Install Memcache

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By default PHP loads and saves sessions to disk. Disk storage has a few problems:

1. Slow IO: Reading from disk is one of the most expensive operations an application can perform, aside from reading across a network.
2. Scale: If we add a second server, neither machine will be aware of sessions on the other.

Enter Memcached
I hinted at Memcached before as a content cache that can improve application performance by preventing trips to the database. Memcached is also perfect for storing session data, and has been supported in PHP for quite some time.

Why use memcached rather than file-based sessions? Memcache stores all of its data using key-value pairs in RAM – it does not ever hit the hard drive, which makes it F-A-S-T. In multi-server setups, PHP can grab a persistent connection to the memcache server and share all sessions between multiple nodes.

Installation
Before beginning, you’ll need to have the Memcached server running. I won’t get into the details for building and installing the program as it is different in each environment. On Ubuntu it’s as easy as aptitude install memcached. Most package managers have a memcached installation available.

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Understanding Linux CPU Load

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You might be familiar with Linux load averages already. Load averages are the three numbers shown with the uptime and top commands – they look like this:

load average: 0.09, 0.05, 0.01

Most people have an inkling of what the load averages mean: the three numbers represent averages over progressively longer periods of time (one, five, and fifteen minute averages), and that lower numbers are better. Higher numbers represent a problem or an overloaded machine. But, what's the the threshold? What constitutes "good" and "bad" load average values? When should you be concerned over a load average value, and when should you scramble to fix it ASAP?

First, a little background on what the load average values mean. We'll start out with the simplest case: a machine with one single-core processor.

The traffic analogy

A single-core CPU is like a single lane of traffic. Imagine you are a bridge operator … sometimes your bridge is so busy there are cars lined up to cross. You want to let folks know how traffic is moving on your bridge. A decent metric would be how many cars are waiting at a particular time. If no cars are waiting, incoming drivers know they can drive across right away. If cars are backed up, drivers know they're in for delays.

So, Bridge Operator, what numbering system are you going to use? How about:

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Reset root Password for Redhat/CentOS/Sl Linux 5.x

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You can log in using single-user mode and create a new root password.

To enter single-user mode, reboot your computer. If you use the default boot loader, GRUB, you can enter single user mode by performing the following:

  1. At the boot loader menu, use the arrow keys to highlight the installation you want to edit and type [A] to enter into append mode.

  2. You are presented with a prompt that looks similar to the following:

    grub append> ro root=LABEL=/

  3. Press the Spacebar once to add a blank space, then add the word single to tell GRUB to boot into single-user Linux mode. The result should look like the following:

    ro root=LABEL=/ single

  4. Press [Enter] and GRUB will boot single-user Linux mode. After it finishes loading, you will be presented with a shell prompt similar to the following:

    sh-2.05b#

  5. You can now change the root password by typing

    passwd root

    You will be asked to re-type the password for verification. Once you are finished, the password will be changed. You can then reboot by typing reboot at the prompt; then you can log in to root as you normally would.

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