inside a cluster

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This is where we start looking at the infrastructure of the LIC. Things get more technical from here. All the technology is explained in the following pages.

The customer services available in the LIC advertise the goods and take the orders. These layers need skilled technical people to keep them running. A service runs on a host. A host is combination of hardware and software that provide one set of system services. An Internet server is the software that gives access to Internet resources. Internet resources are data files containing electronic representations of just about everything.

what it is

This chapter gives an overview what the LIC is, its place in the big wide world and what makes up the LIC. There are all sorts of technological things in the LIC. so to keep things simple we start with concepts and finish with the small details. I assume that writing a horribly complicated shopping list of all the parts that an LIC contains will twist your melon.

All sorts of technological things make up the LIC. It contains everything needed to run web sites: computers, operating systems, web servers, website content and so on. Some things you can touch, such as the computer boxes, and most you can't, like Internet services. Luckily, you don't need to understand these things at this point. It is all explained later. The way all these things fit together is the architecture of the LIC.

LIC table: things
type of thing things description
applications firewalls, ISP links, web servers, application servers, database servers, NIDS, backup servers, reporting servers, event monitors These are the programs that make the LIC do things.
languages bourne shell, php, perl, sql, C Some programming is done in these languages.
protocols CGI, DNS, FTP, HTML, HTTP, HTTPS IP, LDAP, LDIF, RAID, SMTP, SSH, SSL, TCP, VPN A protocol is a common format that two computers use to talk to each other. A service
operating systems solaris, linux, cisco IOS, Microsoft XP We use utilities supplied with these OSs.
data center components cables, routers, hubs, patch panels, racks, air conditioners, fire suppressors, alarm systems, computers These are the things in the LIC that can be touched.

The architecture of the LIC has something in common with the architecture of a building. Half the components are used to build the network - the structure of the LIC. The other half are applications and services that use the LIC. If the LIC was a office block, the network would be the bricks, mortar and crappy coffee machine and the applications would be the employees who do the work. The rest of this chapter describes the components of the network architecture and the components of the application architecture.

the network architecture

The network architecture describes the wet string and baked bean tins that connect the Internet on one side to the enterprise network on the other.The LIC network lies between the Internet and the enterprise network and so is a target for every fun-loving Internet pirate. To make it more difficult to get from the nasty Internet to the delicate unprotected enterprise network, the LIC network has three lines of defense. An Internet bad guy has to cross all three to make it to the enterprise network. Inside each line of defense is an area called a DMZ (De-Militarised Zone).

LIC topology:
groups of computers

Computers in the LIC are grouped together according to the function they provide. That function may be straightforward, such as providing an extranet web service, or a little more abstract such as providing business logic services. Each group of computers forms a LAN (Local Area Network). A LAN is a group of computers that share network traffic. Each DMZ in the LIC contains a few LANs.

Like Tupperware parties, each Internet service is provided by a host. A host is the hardware and software that provide one set of system services. A web service can be provided by an IBM PC, the Linux operating system and the Apache web server application: the PC and the OS together make up the host. All computers in the LIC, except for some of the network computers, are hosts. The busier the LIC is, the more hosts it needs to provide services. Each group of hosts that do a similar thing are connected together to form a LAN.

All the physical bits and pieces are represented in the coming pages using simple shapes and pretty pictures. In reality they are a clunky collection of ugly boxes and spaghetti cabling that needs to be housed somewhere. That somewhere is the data center.

the application architecture

The structure of the network supports the structure of the applications. The services that a web site provides are made up of lots of applications. The LIC provides all popular applications so web site engineers can use them to build their sites. If new or unusual applications are required then it is easy to add them. The application architecture describes what applications are in the LIC and the way applications are used to build a web site.

All the types of applications and services are listed in the final part of this chapter. Some of the services are at the business end of the LIC and are used directly by customers, such as DNS servers and web servers. Others work behind the scenes, such as database servers and LDAP servers.

Web site architects usually design sites based on a three tier model. The three tier model divides a service into a client tier, a business logic tier and a business data tier. The Internet is the client tier (where the customers are), the LIC is the business logic tier and the enterprise network is the business data tier.

what it isn't

Complete. This is an abstract view, not a nook and cranny view. For instance, it does not cover the ISP links which are essential to connect an Internet data center to the Internet. The pages in car-size cluster architecture make a detailed guide to what makes up the LIC.

where it is

These pages show the components of the LIC in one pretty network picture. In the real world, the components of an LIC may all be in the same room or half a world apart.