This article continues mini-series started with the post Introduction to Firewall Builder 4.0. This article is also available as a section in the “Firewall Builder Cookbook” chapter of Firewall Builder Users Guide 4.0.
Firewall Builder 4.0 is currently in beta testing phase. If you find it interesting after reading this post, please download and try it out. Source code archives, binary deb and rpm packages for popular Linux distributions and commercially distributed Windows and Mac OS X packages are available for download here.
In this post I demonstrate how Firewall Builder can be used to generate firewall configuration for a clustered web server with multiple virtual IP addresses. The firewall is running on each web server in the cluster. This example assumes the cluster is built with heartbeat using “old” style configuration files, but which high availability software is used to build the cluster is not really essential. I start with the setup that consists of two identical servers running Linux but in the end of the article I am going to demonstrate how this configuration can be converted to OpenBSD with CARP.
This entry is part 1 of 4 in the series Linux Firewall Cluster Configuration with Firewall Builder v4.:
Condor is a specialized workload management system for compute-intensive jobs. It provides a job queuing mechanism, scheduling policy, priority scheme, and resource monitoring and management.
Xen is one of the leading Virtualization software. You can use Xen virtualization to implement HA clusters. However, there are few issues you must be aware of while handling failures in a high-availability environment. This article explains configuration options using Xen:
The idea of using virtual machines to build high available clusters is not new. Some software companies claim that virtualization is the answer to your HA problems, off course that’s not true. Yes, you can reduce downtime by migrating virtual machines to another physical machine for maintenance purposes or when you think hardware is about to fail, but if an application crashes you still need to make sure another application instance takes over the service. And by the time your hardware fails, it’s usually already too late to initiate the migration.
So, for each and every application you still need to look at whether you want to have it constantly available, if you can afford the application to be down for some time, or if your users won’t mind having to relogin when one server fails.
=> Using Xen for High Availability Clusters [onlamp.com]
My previous article related to iSCSI storage and NAS storage brought a couple of questions. An interesting question from my mail bag:
I’ve 5 Debian Linux servers with HP SAN box. Should I boot from SAN?
No, use centralized network storage for shared data or high availability configuration only. Technically you can boot and configure system. However I don’t recommend booting from SAN or any other central server until and unless you need diskless nodes:
[a] Use local storage – Always use local storage for /boot and / (root) filesystem
[b] Keep it simply – Booting from SAN volumes is complicated procedure. Most operating systems are not designed for this kind of configuration. You need to modify scripts and booting procedure.
[c] SAN booting support – Your SAN vendor must support platform booting a Linux server. You need to configure HBA and SAN according to vendor specification. You must totally depend upon SAN vendor for drivers and firmware (HBA Bios) to get thing work properly. General principle – don’t put all your eggs in one basket err one vendor ;)
[d] Other factors – Proper fiber channel topology must be used. Make sure Multipathing and redundant SAN links are used. The boot disk LUN is dedicated to a single host. etc
As you can see, complications started to increases, hence I don’t recommend booting from SAN.
Arun Singh shows us how to create shared storage on SUSE Linux Enterprise Server 10 using OCFS2 (Oracle Cluster File System v2 for shared storage) and Xen Virtualization technology. Enterprise grade shared storage can cost you lots of money but here no real expensive shared storage used. The information provided here works with real shared storage as well:
This paper is to help you to understand the steps involved in creating shared storage without using expensive shared storage. Using this information you can create shared storage used by all xen guest OS and Host, avoiding copying of files between guest OS’s. Hope you will find this paper useful.
You can easily port instructions to Redhat or any other Linux distro without a problem. You can also use Redhat’s Global File System (GFS) too. We often use Fibre Channel or iSCSI, devices for GFS shared storage.
Creating shared storage on SUSE Linux Enterprise Server 10 using Xen and OCFS2 [novell.com]
On a related note there is also article about creating a highly available VMware Server environment on a Debian Etch system.