Load Balancer Open Source Software

Posted on in Categories Hardware, High performance computing, Linux, Linux Scalability, Linux Virtualization, Monitoring, Networking, RedHat/Fedora Linux, Storage last updated March 11, 2008

I’ve worked with a various load balancing systems (LBS). They are complex pieces of hardware and software. In this post I will highlight some of the open source load balancing software. But what is load balancing?
It is nothing but a technique used to share (spared) load / services between two or more servers. For example, busy e-commerce or bank website uses load balancer to increase reliability, throughput, uptime, response time and better resource utilization. You can use following softwares as an advanced load balancing solution for web, cache, dns, mail, ftp, auth servers, VoIP services etc.

Linux Virtual Server (LVS)

LVS is ultimate open source Linux load sharing and balancing software. You can easily build a high-performance and highly available server for Linux using this software. From the project page:

Virtual server is a highly scalable and highly available server built on a cluster of real servers. The architecture of server cluster is fully transparent to end users, and the users interact with the cluster system as if it were only a single high-performance virtual server.

=> Project Web Site

Red Hat Cluster Suite

It is a high availability cluster software implementation from Linux leader Red Hat. It provide two type services:

  1. Application / Service Failover – Create n-node server clusters for failover of key applications and services
  2. IP Load Balancing – Load balance incoming IP network requests across a farm of servers

=> Product web page

The High Availability Linux Project

Linux-HA provides sophisticated high-availability (failover) capabilities on a wide range of platforms, supporting several tens of thousands of mission critical sites.

=> Project web site

Ultra Monkey

Ultra Monkey is a project to create load balanced and highly available network services. For example a cluster of web servers that appear as a single web server to end-users. The service may be for end-users across the world connected via the internet, or for enterprise users connected via an intranet.

Ultra Monkey makes use of the Linux operating system to provide a flexible solution that can be tailored to a wide range of needs. From small clusters of only two nodes to large systems serving thousands of connections per second.

=> Project web site

Personally, I’ve worked with both LVS and Red Hat Cluster Suite and I highly recommend these softwares.

FreeBSD List / Display Open Ports With sockstat Command

Posted on in Categories FreeBSD, Hardware, Howto, Monitoring, Networking last updated February 8, 2008

You can use traditional netstat / lsof command to lists open Internet or UNIX domain sockets on FreeBSD. FreeBSD comes with a simple and easy to use command called sockstat.
The -4 option only displays IPv4 sockets.

The -6 option only displays IPv6 sockets.

The -c option only displays connected sockets.

The -l option only displays listening sockets (open port).

For example, display IPv4 related open ports, enter:
# sockstat -4 -l

root     sendmail   653   3  tcp4          *:*
root     sshd       647   3  tcp4        *:*
root     ntpd       616   4  udp4   *:123                 *:*

Here the equivalent of netstat:
$ netstat -nat | grep LISTEN
For information read sockstat command man page:
$ man sockstat

Find and Fix Linux Latency Problem with LatencyTOP Software

Posted on in Categories GNU/Open source, Howto, Linux, Linux desktop, Monitoring, Troubleshooting, Tuning last updated January 19, 2008

A TOP-like tool for monitoring system latency and its causes for Linux system.

The Intel Open Source Technology Center is pleased to announce the release of version 0.1 of LatencyTOP, a tool for developers to visualize system latencies. Skipping audio, slower servers, everyone knows the symptoms of latency. But to know what’s going on in the system, what’s causing the latency, how to fix it… that’s a hard question without good answers right now.

LatencyTOP is a Linux tool for software developers (both kernel and userspace), aimed at identifying where in the system latency is happening, and what kind of operation/action is causing the latency to happen so that the code can be changed to avoid the worst latency hiccups.
Linux Latency Problem with LatencyTOP Software
(Fig. 01: LatencyTOP in Action [ Image Credit: Intel Corp. ])

Download LatencyTOP

=> Visit official project site to download LatencyTOP software. Please note that you also need to patch Linux kernel.

Security Tip: Avoid Detection with nmap Port Scan Decoys

Posted on in Categories Howto, Linux, Monitoring, Networking, Security, Sys admin, UNIX last updated January 8, 2008

You can test your IDS or IPS devices to monitor your scan traffic. Use this feature to avoid detection with nmap. You may not want to get caught performing a network scan. For example, using following technique you can test your own IDS / IPS / network security from remote location or home.

nmap Decoy option – Cloak a scan with decoys

nmap has -D option. It is called decoy scan. With -D option it appear to the remote host that the host(s) you specify as decoys are scanning the target network too. Thus their IDS might report 5-10 port scans from unique IP addresses, but they won’t know which IP was scanning them and which were innocent decoys. While this can be defeated through router path tracing, response-dropping, and other active mechanisms, it is generally an effective technique for hiding your IP address.

You can separate each decoy host with commas, and you can optionally use ME as one of the decoys to represent the position for your real IP address. If you put ME in the 6th position or later, some common port scan detectors (such as Solar Designer’s excellent scanlogd) are unlikely to show your IP address at all. If you don’t use ME, nmap will put you in a random position. Note that the hosts you use as decoys should be up or you might accidentally SYN flood your targets. Also it will be pretty easy to determine which host is scanning if only one is actually up on the network. You might want to use IP addresses instead of names (so the decoy networks don’t see you in their nameserver logs).

WARNING! These penetration testing (security testing) examples may be considered as Unauthorized Access or Illegal Behavior. Use examples on your own RISK and/or to secure your own network host / IPS /IDS.

Use the following syntax:
# nmap -n -Ddecoy-ip1,decoy-ip2,your-own-ip,decoy-ip3,decoy-ip4 remote-host-ip
# nmap -n -D192.168.1.5,,,

Host (or network IDS / IPS) will see 4 port scan and remote host / IDS has no way telling which one was real. Decoys are used both in the initial ping scan (using ICMP, SYN, ACK, or whatever) and during the actual port scanning phase. Decoys are also used during remote OS detection (-O). Decoys do not work with version detection or TCP connect scan. It is worth noting that using too many decoys may slow your scan and potentially even make it less accurate. Also, some ISPs will filter out your spoofed packets, but many do not restrict spoofed IP packets at all.

nmap ideal scan technique to hide your IP

Following example, uses an an idle scan technique. It uses port 1234 on IP as as a zombie to scan host –
# nmap -P0 -sI

This technique only hides your source address but remote IPS / IDS always record and logs scan. Please refer to nmap man page for more information:
man nmap

Linux display disk total statistics including time spent reading and writing data

Posted on in Categories File system, Hardware, Linux, Monitoring last updated January 3, 2008

Most Linux admins are not aware of hidden switch (undocumented switch) called -D. The -D option display a nice summery of disk I/O subsystem since boot time. Output includes total time spent reading and writing data, merged reads and merged writes (kernel disk i/o optimization technique) and other parameters.
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