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 machines   Is this just to make sure that if one server is compromised  both systems aren t accessible   Do the security concerns outweigh the complexity of two servers  extra cost  dedicated network connection between the two  more maintenance  etc    especially for a small application  where neither piece is using too much CPU or memory   Even with two servers  with one server compromised  an attacker could still do serious damage  either by deleting the database  or messing with the application code     Why would this be such a big deal if performance isn t an issue

User · Answer

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.

User · Answer

Ok  Here is the thing  it is more Secure to have your DB Server installed on another Machine and your Application on the Web Server  You then connect your application to the DB with a Web Link  Thanks it

User · Answer

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

User · Answer

Security  Your web server lives in a DMZ  accessible to the public internet and taking untrusted input from anonymous users  If your web server gets compromised  and you ve followed least privilege rules in connecting to your DB  the maximum exposure is what your app can do through the database API  If you have a business tier in between  you have one more step between your attacker and your data  If  on the other hand  your database is on the same server  the attacker now has root access to your data and server  Scalability  Keeping your web server stateless allows you to scale your web servers horizontally pretty much effortlessly  It is very difficult to horizontally scale a database server  Performance  2 boxes   2 times the CPU  2 times the RAM  and 2 times the spindles for disk access     All that being said  I can certainly see reasonable cases that none of those points really matter

User · Answer

I think its because the two machines usually would need to be optimized in different ways   Other than that I have no idea  we run all our applications with the server-database on the same machine - granted we re not public facing - but we ve had no problems   I can t imagine that too many people care about one machine being compromised over both since the web application will usually have nearly unrestricted access to at the very least the data if not the schema inside the database   Interested in what others might say

User · Answer

Security is a major concern  Ideally your database server should be sitting behind a firewall with only the ports required to perform data access opened  Your web application should be connecting to the database server with a SQL account that has just enough rights for the application to function and no more  For example you should remove rights that permit dropping of objects and most certainly you shouldn t be connecting using accounts such as  sa    In the event that you lose the web server to a hijack  i e  a full blown privilege escalation to administrator rights   the worst case scenario is that your application s database may be compromised but not the whole database server  as would be the case if the database server and web server were the same machine   If you ve encrypted your database connection strings and the hacker isn t savvy enough to decrypt them then all you ve lost is the web server

User · Answer

I would think the big factor would be performance   Both the web server app code and SQL Server would cache commonly requested data in memory and you re killing your cache performance by running them in the same memory space

User · Answer

Database licences are not cheep and are often charged per CPU  therefore by separating out your web-servers you can reduce the cost of your database licences   E g if you have 1 server doing both web and database that contains 8 CPUs you will have to pay for an 8 cpu licence    However if you have two servers each with 4 CPUs and runs the database on one server you will only have to pay for a 4 cpu licences

User · Answer

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

User · Answer

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

User · Answer

Arguing that there is a real performance gain to be had by running a database server on a web server is a flawed argument   Since Database servers take query strings and return result sets  the data actually flowing from data server to web server is relatively small  but the horsepower required to process the query and generate the result set is relatively large   Optimizing performance around the data transfer time therefore is optimizing around the wrong thing   Regarding security  there are advantages to having the data server on a different box than the web server   Having such a setup is not the be all and end all of security  but it is a step in the right direction   Regarding scalability  it is easy and relatively cheap to add web servers and put them into cluster to handle increased traffic   It is not so easy and cheap to add data servers and cluster them   Also  web servers and data servers have different hardware needs  so multiple boxes help out with scalability   If you are starting small and have only one box  then a good way would go would be to use virtual machines   Running the web server and data server in different VMs on one host gives you all the gains of separate boxes at the cost of one large box price

User · Answer

I can speak from first hand experience that it is often a good idea to place the web server and database on different machines   If you have an application that is resource intensive  it can easily cause the CPU cycles on the machine to peak  essentially bringing the machine to a halt   However  if your application has limited use of the database  it would probably be no big deal to have them share a server

User · Answer

Operating system is another consideration  While your database may require larger memory spaces and therefore UNIX  your web server - or more specifically your app server since you mention only two tiers - may be a  Net-based  and therefore require Windows

User · Answer

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

User · Answer

On the other hand  referring to a different blogging Scott  Watermasyck  of Telligent  - they found that most users could speed up the websites  using Telligent s Community Server   by putting the database on the same machine as the web site   However  in their customer s case  usually the db  amp  web server are the only applications on that machine  and the website isn t straining the machine that much   Then  the efficiency of not having to send data across the network more that made up for the increased strain

User · Answer

An additional concern is that databases like to take up all the available memory and hold it in reserve for when it wants to use it  You can force it to limit the memory but this can considerably slow data access

User · Answer

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

User · Answer

One factor that hasn t been mentioned yet is load balancing   If you start off thinking of the web server and the database as separate machines  you optimize for fewer network round trips and also it gets easier to add a second web server or a second database engine as needs increase

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

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