Although I know something about Linux, apache, DNS, IIS, DHCP, IP addresses and working of Internet I still I cannot find the answer which I am looking for.

What I need:

I am planning to setup a small company which can hosts companies’ websites (maximum 500 companies) and email as well. By the way I don’t want to be ISP (Internet service provider). My target is for small companies, (only those sites, which are about max 100 pages, and are static, HTML pages, later on may be small databases MySql, and PHP)

My questions are:

1. How many computer I will need, and for what purposes, like Web Server, email server, FTP server, etc?
2. How many DNS server I need?
3. Can I make DNS sever, Web server (apache) and mail server on same PC, If not why?
4. What about security and database support? What if I need to expand later on, how difficult is that?
5. Which platform is easy and secure for my company, Linux or Windows?

It's generally best to keep these services on their own machines for many reasons. Here's a few reasons:

1) You start to get a lot of clients who start generating a lot of traffic, thus keeping DNS, APACHE, SMTP and POP3 pretty active.. This is going to slow down the machine and piss your clients off because it's taking 8 seconds for their entire site to load instead of the previous 3 seconds, clients end up leaving you and posting bad reviews about you..

2) If you decide to expand the business in the future, it's going to be a LOT easier to upgrade individual machines with services on them, instead of having to migrate the services over to new machines. This is especially true for apache and dns. If you get 500 clients, it's going to be a pain the arse to migrate DNS and APACHE off to their own machines..

3) And most importantly.. If someone hacks one of your services, that means they've hacked ALL of your services. For example, i exploit your Apache release.. Now I have controll over your apache server, sendmail server, DNS server, pop3 server and whatever else interesting you might have stored on that machine because you wished to only use one machine.

Hope this helps you some.. I'm sure other people will have their 2 cents to add to this..

Also,
If you are up to the cost, then you could buy cpanel so that the clients could edit their sites from anywhere. It would be a better idea for you to have your different services on different computers so that they wouldn't be easily hijacked. Also, it would be good to have your dns servers at least in different cities. It would also be good for the other computers, but if it's easier, just keep them in the same place. I'm not going to use multiple computers only because I'm just going to host like 3 websites.

Thank you everybody for replying very fast and keeping this forum alive.
In my case, how many computer I need?
One for DNS, one for Apache (web hosting) another for mail server. Any more.. server I need???

You will also need a computer have the internet connection, which will have to connect to the internet then share it with the other computers. That computer can be any of those computers, or another. How would you be connecting to the internet. Then I will tell you what I think your set up should be..

Consider:
High Speed Internet
Business Internet
xDSL
DSL

Thank 'esher2292'
I hope you will guide me to setup all these Machines...
DNS, Apache, POP3, SMTP, etc....

You are welcome. For one thing, dial-up is not a good option. Most of the time you will connect to some sort of modem using an ethernet cable. So you will need two cards if you want to use a wired network. One to connect to the internet and one to go out to a router. Then you would connect the other pc's to the router. Then you can go and set everything up! I hope that you get everything set up right. If you need help with anything, I'm sure that either I or someone will be able to help you

If you need help, just ask. In case I don't respond email me telling me to look at the site because sometimes I forget to look here!

Also, you'll need to have two DNS servers, one primary, one backup. You can run BIND (the DNS server) on an old 486 or Pentium, so other than the Internet connection, this shouldn't be a problem.

I am going to connect my PC to Internet via broadband line. I hope this is good option (I don't know about other option apart from dial-up, which is very slow!!!!), you can advice me any other option in my case!!!

Can some one advice me what software I need to install on Linux system for DNS, and Mail server, and how can I monitor network traffic and security, what software I need to install.

I know about apache and MySql, and have successfully installed, but still some problem with PHP!!! What bout CGI, and JSP how can I provide these facility on my Linux web server, what software I need to Install and configure?

OK, guy thanks, I will ask you people when I face the problem.

If you're going to be setting up a hosting company, you'll need servers with static IP address. Most broadband concerns these days assign IP addresses dynamically, and generally charge extra for static IP addresses. You'll need to do a bit of shopping around to see what sort of deals are available in your area. You may get lucky and find a broadband provider that assigns static addresses by default. You will need, at minimum, three static IP addresses, 1 each for your primary and secondary name server, and one for a router/firewall behind which sits your other servers (you could get by with two static IP addresses, and have the router also serve DNS, but this is inadvisable for the reasons given earlier in this thread). Please check your broadband provider's terms of service -- many will want to charge extra if you will be hosting servers on the connection -- again, this will depend on the exact sort of deal you get.

Going into the nuts and bolts of administering everything would require a lot of space. Your best bet is to go to a bookstore, surf the Web, and do some reading up. Briefly here's the list of things you'll probably need to be running:

Domain Name Service (DNS): BIND -- go for version 9.
Mail Transport Agent: I use Sendmail, though Postfix or Qmail would probably be better if you are just starting off (they're easier and more foolproof, or so I hear).
POP3/IMAP Server: I like Dovecot because it's simple to get set up. Look at Courier too.
Web server: Apache (duh) -- get it configured to handle CGIs, PHP, etc. and you're set.
Java (JSPs, Servlets, etc.): I use Tomcat. It's pretty easy to configure and can be integrated w/ Apache, though I've never actually tried the latter.

I'm sure others will have more opinions on software -- I'm mostly going with what I know/have used here.

Also, if you're going to be selling these services you'll need to manage things like backups, disaster recovery. What happens if power goes out at your home (or wherever you're hosting this)? You might look at colocating your servers at a facility that will take care of this for you, but that can get very expensive in a hurry. At the minimum, you'll need a good UPS on all the machines.

Anyhow, good luck with it all...

Thank you
btmiller

Your technical detail will help Me very much, yeah you are right I have to survey the market!!! Any advice you are welcome most!!!

qmail is rather hard to set up but very secure if you are looking for a mailserver.

Also for serving DNS requests you will need two static IPs.