HowtoForge - Linux Howtos and Tutorials - High-Availability

The Perfect Load-Balanced & High-Availability Web Cluster With 2 Servers Running Xen On Ubuntu 8.04 Hardy Heron

Thu, 09 Oct 2008 21:17:43 +0200

The Perfect Load-Balanced & High-Availability Web Cluster With 2 Servers Running Xen On Ubuntu 8.04 Hardy Heron

In this howto we will build a load-balanced and high-availability web cluster on 2 real servers with Xen, hearbeat and ldirectord. The cluster will do http, mail, DNS, MySQL database and will be completely monitored. This is currently used on a production server with a couple of websites. The goal of this tutorial is to achieve load balancing & high availability with as few real servers as possible and of course, with open-source software. More servers means more hardware & hosting cost.

Centralized Backup Server With Amanda On CentOS

Tue, 30 Sep 2008 14:43:06 +0200

Centralized Backup Server With Amanda On CentOS

This document describes how to set up a centralized network backup with Amanda. We will use virtual tape to store the backup.

How To Set Up DHCP Failover On Centos 5.1

Wed, 25 Jun 2008 19:14:39 +0200

How To Set Up DHCP Failover On Centos 5.1

This tutorial will walk you through setting up DHCP fail over on CentOS 5.1 using the default ISC dhcp server, this can easily be adapted to any other Linux distro out there. You will most likely need Failover in environments where network down time can not be tolerated. My home is running a DLNA setup so I need my devices to be able to obtain network parameters at all times.

How To Set Up A Load-Balanced MySQL Cluster With MySQL 5.1

Sun, 15 Jun 2008 19:21:08 +0200

How To Set Up A Load-Balanced MySQL Cluster With MySQL 5.1

This tutorial is based on Falko Timme's tutorial for MySQL Cluster 5.0. It shows how to configure a MySQL 5.1 cluster with five nodes: 1 x management, 2 x storage nodes and 2 x balancer nodes. This cluster is load-balanced by an Ultra Monkey package which provides heartbeat (for checking if the other node is still alive) and ldirectord (to split up the requests to the nodes of the MySQL cluster).

How To Set Up A Loadbalanced High-Availability Apache Cluster Based On Ubuntu 8.04 LTS

Tue, 10 Jun 2008 19:09:27 +0200

How To Set Up A Loadbalanced High-Availability Apache Cluster Based On Ubuntu 8.04 LTS

This tutorial shows how to set up a two-node Apache web server cluster that provides high-availability. In front of the Apache cluster we create a load balancer that splits up incoming requests between the two Apache nodes. Because we do not want the load balancer to become another "Single Point Of Failure", we must provide high-availability for the load balancer, too. Therefore our load balancer will in fact consist out of two load balancer nodes that monitor each other using heartbeat, and if one load balancer fails, the other takes over silently.

Monitoring UPS Power Status Using Network UPS Tools (NUT) 2.2.0 on Multiple OpenSuSE 10.3 Servers

Mon, 14 Apr 2008 16:54:44 +0200

Monitoring UPS Power Status Using Network UPS Tools (NUT) 2.2.0 on Multiple OpenSuSE 10.3 Servers

Network UPS Tools is a collection of programs which provide a common interface for monitoring and administering UPS hardware. The primary goal of the Network UPS Tools (NUT) project is to provide reliable monitoring of UPS hardware and ensure safe shutdowns of the systems which are connected. This document describes how to configure one machine connected to the UPS so it monitors the power status. This can relay alerts to other machines that are running off the same power line. This way, multiple servers can perform a safe shutdown in case of power failure.

Setting Up A High-Availability Load Balancer (With Failover and Session Support) With HAProxy/Heartbeat On Fedora 8

Thu, 28 Feb 2008 18:16:33 +0100

Setting Up A High-Availability Load Balancer (With Failover and Session Support) With HAProxy/Heartbeat On Fedora 8

This document describes how to set up a two-node load balancer in an active/passive configuration with HAProxy and heartbeat on Fedora 8. The load balancer acts between the user and two (or more) Apache web servers that hold the same content. The load balancer passes the requests to the web servers and it also checks their health. If one of them is down, all requests will automatically be redirected to the remaining web server(s). In addition to that, the two load balancer nodes monitor each other using heartbeat. If the master fails, the slave becomes the master - users won't notice any disruption of the service. HAProxy is session-aware - you can use it with any web application that makes use of sessions like forums, shopping carts, etc.

Master-Master Replication With MySQL 5 On Fedora 8

Sun, 17 Feb 2008 19:06:15 +0100

Master-Master Replication With MySQL 5 On Fedora 8

This document describes how to set up master-master replication with MySQL 5 on Fedora 8. Since version 5, MySQL comes with built-in support for master-master replication, solving the problem that can happen with self-generated keys. In former MySQL versions, the problem with master-master replication was that conflicts arose immediately if node A and node B both inserted an auto-incrementing key on the same table. The advantages of master-master replication over the traditional master-slave replication are that you don't have to modify your applications to make write accesses only to the master, and that it is easier to provide high-availability because if the master fails, you still have the other master.

Sample Configuration of DRBD On CentOS 4.5

Thu, 20 Dec 2007 10:12:45 +0100

Sample Configuration of DRBD On CentOS 4.5

DRBD is an abbreviation of Distributed Replicated Block Device. DRBD is a block device which is designed to build high-availability clusters. This is done by mirroring a whole block device via (a dedicated) network. You could see it as a network RAID1.

Setting Up A High-Availability Load Balancer (With Failover and Session Support) With HAProxy/Heartbeat On Debian Etch

Tue, 06 Nov 2007 12:50:26 +0100

Setting Up A High-Availability Load Balancer (With Failover and Session Support) With HAProxy/Heartbeat On Debian Etch

This article explains how to set up a two-node load balancer in an active/passive configuration with HAProxy and heartbeat on Debian Etch. The load balancer sits between the user and two (or more) backend Apache web servers that hold the same content. Not only does the load balancer distribute the requests to the two backend Apache servers, it also checks the health of the backend servers. If one of them is down, all requests will automatically be redirected to the remaining backend server. In addition to that, the two load balancer nodes monitor each other using heartbeat, and if the master fails, the slave becomes the master, which means the users will not notice any disruption of the service. HAProxy is session-aware, which means you can use it with any web application that makes use of sessions (such as forums, shopping carts, etc.).

Setting Up A High-Availability Load Balancer (With Failover and Session Support) With Pound/Keepalived On Debian Etch

Fri, 02 Nov 2007 18:53:38 +0100

Setting Up A High-Availability Load Balancer (With Failover and Session Support) With Pound/Keepalived On Debian Etch

This article explains how to set up a two-node load balancer in an active/passive configuration with Pound and keepalived on Debian Etch. The load balancer sits between the user and two (or more) backend Apache web servers that hold the same content. Not only does the load balancer distribute the requests to the two backend Apache servers, it also checks the health of the backend servers. If one of them is down, all requests will automatically be redirected to the remaining backend server. In addition to that, the two load balancer nodes monitor each other using keepalived, and if the master fails, the slave becomes the master, which means the users will not notice any disruption of the service. Pound is session-aware, which means you can use it with any web application that makes use of sessions (such as forums, shopping carts, etc.).

Merging Multiple Apache Access Logs Into One Overall Access Log

Mon, 29 Oct 2007 11:37:58 +0100

Merging Multiple Apache Access Logs Into One Overall Access Log

Let's assume you have a web application that runs of a cluster of Apache nodes. Each node generates its own Apache access log from which you can generate page view statistics with tools such as Webalizer or AWStats. Obviously you do not want to have page view statistics for each Apache node, but overall page view statistics. To achieve this, we must merge the access logs from each node into one overall access log that we can then feed into Webalizer or AWstats. There is a Perl script called logresolvemerge.pl (part of the AWStats package) that can do this for us.

Setting Up A High-Availability Load Balancer (With Failover and Session Support) With HAProxy/Keepalived On Debian Etch

Fri, 26 Oct 2007 11:21:33 +0200

Setting Up A High-Availability Load Balancer (With Failover and Session Support) With HAProxy/Keepalived On Debian Etch

This article explains how to set up a two-node load balancer in an active/passive configuration with HAProxy and keepalived on Debian Etch. The load balancer sits between the user and two (or more) backend Apache web servers that hold the same content. Not only does the load balancer distribute the requests to the two backend Apache servers, it also checks the health of the backend servers. If one of them is down, all requests will automatically be redirected to the remaining backend server. In addition to that, the two load balancer nodes monitor each other using keepalived, and if the master fails, the slave becomes the master, which means the users will not notice any disruption of the service. HAProxy is session-aware, which means you can use it with any web application that makes use of sessions (such as forums, shopping carts, etc.).

Setting Up Master-Master Replication With MySQL 5 On Debian Etch

Tue, 23 Oct 2007 18:03:49 +0200

Setting Up Master-Master Replication With MySQL 5 On Debian Etch

Since version 5, MySQL comes with built-in support for master-master replication, solving the problem that can happen with self-generated keys. In former MySQL versions, the problem with master-master replication was that conflicts arose immediately if node A and node B both inserted an auto-incrementing key on the same table. The advantages of master-master replication over the traditional master-slave replication are that you don't have to modify your applications to make write accesses only to the master, and that it is easier to provide high-availability because if the master fails, you still have the other master.

Apache: Creating A Session-Aware Loadbalancer Using mod_proxy_balancer (Debian Etch)

Tue, 29 May 2007 17:42:21 +0200

Apache: Creating A Session-Aware Loadbalancer Using mod_proxy_balancer (Debian Etch)

Since Apache 2.1, a new module called mod_proxy_balancer is available which lets you turn a system that has Apache installed into a loadbalancer. This loadbalancer retrieves requested pages from two or more backend webservers and delivers them to the user's computer. Users get the impression that they deal with just one server (the loadbalancer) when in fact there are multiple systems behind the loadbalancer that process the users' requests. By using a loadbalancer, you can lower the load average on your webservers. One important feature of mod_proxy_balancer is that it can keep track of sessions which means that a single user always deals with the same backend webserver. Most websites are database-driven nowadays with user logins etc., and you'd get weird results if a user logs in on one backend webserver, and then his next request goes to another backend webserver, meaning he'd get logged out again. You can avoid this by using mod_proxy_balancer's session-awareness.