Why is it not advisable to have the database and web server on the same machine?

Question

Listening to Scott Hanselman\'s interview with the Stack Overflow team (part 1 and 2), he was adamant that the SQL server and application server should be on separate machin

Answer 1

It doesn't really matter (you can quite happily run your site with web/database on the same machine), it's just the easiest step in scaling..

It's exactly what StackOverflow did - starting with single machine running IIS/SQL Server, then when it started getting heavily loaded, a second server was bought and the SQL server was moved onto that.

If performance is not an issue, do not waste money buying/maintaining two servers.

Answer 2

I agree with Daniel Earwicker - the security question is pretty much flawed.

If you have a single box setup with a webserver and only the database for that webserver on it, if that webserver is compromised you lose both the webserver and only the database for that specific application.

This is exactly the same as what happens if you lose the webserver on a 2-server setup. You lose the web server, and just the database for that specific application.

The argument that 'the rest of the DB server's integrity is maintained' where you have a 2-server setup is irrelevant, because in the first scenario, every other database server relating to every other application (if there are any) remain unaffected as well - being, as they are, hosted elsewhere.

Similarly, to the question posed by Kev 'what about all the other databases residing on the DB server? All you've lost is one database.'

• if you were hosting an application and database on one server, you would only host databases on that server which related to that application. Therefore, you would not lose any additional databases in a single server setup when compared to a multiple server setup.

By contrast, in a 2 server setup, where the attacker had access to the Web Server, and by proxy, limited rights (in the best case scenario) to the database server, they could put the databases of every other application at risk by carrying out slow, memory intensive queries or maximising the available storage space on the database server. By separating the applications out into their own concerns, very much like virtualisation, you also isolate them for security purposes in a positive way.

Answer 3

Wow, No one brings up the fact that if you actually buy SQL server at 5k bucks, you might want to use it for more than your web application. If your using express, maybe you don't care. I see SQL servers run Databases for 20 to 30 applicaitions, so putting it on the webserver would not be smart.

Secondly, depends on whom the server is for. I do work for financial companies and the govt. So we use a crazy pain in the arse approach of using only sprocs and limiting ports from webserver to SQL. So if the web app gets hacked. The only thing the hacker can do is call sprocs as the user account on the webserver is locked down to only see/call sprocs on the DB. So now the hacker has to figure out how to get into the DB. If its on the web server well its kind of easy to get to.

Answer 4

Tom is correct on this. Some other reasons are that it isn't cost effective and that there are additional security risks.

Webservers have different hardware requirements than database servers. Database servers fare better with a lot of memory and a really fast disk array while web servers only require enough memory to cache files and frequent DB requests (depending on your setup). Regarding cost effectiveness, the two servers won't necessarily be less expensive, however performance/cost ratio should be higher since you don't have to different applications competing for resources. For this reason, you're probably going to have to spend a lot more for one server which caters to both and offers equivalent performance to 2 specialized ones.

The security concern is that if the single machine is compromised, both webserver and database are vulnerable. With two servers, you have some breathing room as the 2nd server will still be secure (for a while at least).

Also, there are some scalability benefits since you may only have to maintain a few database servers that are used by a bunch of different web applications. This way you have less work to do applying upgrades or patches and doing performance tuning. I believe that there are server management tools for making these tasks easier though (in the single machine case).

Answer 5

I listened to that podcast, and it was amusing, but the security argument made no sense to me. If you've compromised server A, and that server can access data on server B, then you instantly have access to the data on server B.

Answer 6

It depends on the application and the purpose. When high availability and performance is not critical, it's not bad to not to separate the DB and web server. Especially considering the performance gains - if the appliation makes a large amount of database queries, a considerable amount of network load can be removed by keeping it all on the same system, keeping the response times low.