Friday, May 1, 2015

Production Support Incident 6: Bad Architecture Design Database server Box having IIS webserver

Architecture Scenario:
A shared database SQL Server physical box or VM contains shared databases which is connected to different web servers hosted with different website. Lets assume within that database box we have IIS configured with WCF hosted service. The initial objective would be the wcf service which is present within database server must be using database table for storing service data. This is bad design.

What is the problem?
Now when we allocate RAM to SQL server box , sql server consumes all the RAM and keep very little RAM for OS activity. Now lets assume we have IIS configured with wcf service with database server and there is very little RAM available for IIS and OS as SQL server consumes most of the RAM memory . In such case there is going to be memory overflow or Network IO wait conditions for website request that are sending requests to this wcf service hosted in IIS that resides within this database server.

Workaround: You have to explicitly allocate RAM for sql server and for IIS to process the requests. The flipside is your sql server may started getting load and RAM consumption may shoot up to peek which may results in Suspended transactions and process requests with latency.

This is design flaw at infrastructure Level hence it is always important to make assessment and revisit architecture.

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