5 minutes in a DBA's head - Separating the Application and Database server

I was in conversation with an Application owners who said “I have a new product we need to install. The vendor documentation supports both co-located application and database server , and also remote access to the database server”

This sort of comment is standard amongst product documentation and in architecture type of conversation. DBAs are asked to to review and ensure the product implementation is in line with the organisation standards and the standardisation standards required in managing large amounts of servers.   

We’re in the age of Server consolidation and services oriented development. Adding Solid State Disk (SSD)  , converged , hyperconverged, commodity hardware or Cloud,Containers ? The list is growing. The main point is it's changed the performance landscape.  In other words, assumptions about the "ideal" architecture are challenged .    

There are pros and cons to both approaches.

==> Instead of competing for CPU/RAM/Disk on the same machine, now they have their own dedicated compute. DB servers and application server often have much different IO patterns. Read\Write ratios can be vastly different, requiring different server configurations and IO path setups.  Working with your infrastructure  administrators and storage specialists you can design the optimal configuration for db server throughput

==> If database server become unavailable, a properly designed client could cache data, and then sync to the database server once it comes back online.

==> Distributing the risk of hardware outage or OS corruption causing an outage. For example, if the application server is unavailable – then at least the database server remains available, allowing some flexibility on HA & recovery

==> Security hardening around database server. 5 easy ways to protect SQL Server against Ransomware attacks

==> More options around Database clustering. High Availability can be a critical service for Enterprise services supporting business continuity

==> Implementing SQL Server Security Policy is potentially easier if database server is segregated

==> Horizontal Scaling – If you start with 1 database server and 1 application server , then it will be easier to expand out to 2 app servers, without reinstalling another db server

==> Cost – Maintaining multiple servers may have licensing and other costs associated