Having Database and Web Server on single EC2 Instance:

On this post we’ll see advantages and disadvantages of Having Database and Web Server on single EC2 Instance. Recently when I was working with one of the client, they were planning for migrating their systems to AWS EC2 and they asked me a simple question “Can we have Database and Web server on single EC2 instance? What are all the advantages and disadvantages of having Database and Web Server on single EC2 instance?” There are several things needs to be considered to answer this question. We thought of document it which can be helpful for the future reference.

Advantages of having Database and Web Server on single EC2 Instance:

Category	Advantages
Security	No Advantages
Performance	Communication easier between App server and DB Server as both are in same host
	If the application 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.
	On AWS if we have App and DB on same machine we need not worry about the region, otherwise we should make sure both DB and App servers are in same availability zone and region.
Load Balancing	On AWS we can get the benefit from Auto Scaling
Maintenance	It makes easier to maintain all App and DB from one place
HA & DR	No Advantages
Cost	Since App and DB sharing the same host it reduces almost half of the price
Scalability	We start using the application and database and we’ll add more resources when required in future using Auto Scaling

Disadvantages of having Database and Web Server on single EC2 Instance:

Category	Disadvantages
Security	Webserver may need to be available for Public internet access and taking untrusted input from anonymous users.
Security	If web server gets compromised then there might be high chances that attacker can get root access on database server too
Performance	Both the web server/app and SQL Server would cache requested data in memory and it strains the cache performance by running them in the same memory space.
	May impact CPU cycles as sharing it between App and database
	Huge I/O impact when we need to share the Disk between App and Database files
	Usually Application and Database servers are having the different hardware requirements. 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.
Load Balancing	It shouldn’t be a problem as long as we are having a proper estimations on App and DB server resource utility, but an unbalanced resource utility might causes a App / DB hang or interruption
Maintenance	No Disadvantages
HA & DR	More recovery time required in-case of any disaster
Cost	Due to performance concern we can only have the databases related to the application sharing the instance, if we have a dedicated DB instance it can serve multiple applications effectively.
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.

Note: Please help us if we are missing anything. Please drop your suggestions in comments.