Strategies and Tactics: Defining SLA (Service Level Agreement)

SLA means different things to different people.   In many companies and organizations, the agreed upon definition can be different between departments and even individuals.

Simply put, an SLA is an agreement between two parties for a service to be provided.  Focusing on websites, the most commonly agreed upon metric comprising SLA is uptime. 

Since there is no gold-standard agreement on how uptime is defined, how do groups and departments within an organization define uptime?

System administrators may define uptime is the amount of time a server is up and running.  They may or may not include the amount of time that a service or application is up and running or that the server is connected to the network.  Advertisements for web hosting companies often tout “99.99% uptime guaranteed”, but rarely define how that number is measured or achieved.  Most likely, the number is based on the amount of uptime that the server is powered on and “online”

Application developers and webmasters may define uptime as the amount of time that a web server is up and running.  They may or may not include the amount of time that a specific page is being served error free.  If uptime were measured at the web service level, uptimes would realistically be between 95-98%.

People in Sales and Marketing may define uptime as the amount of time that the customer is not complaining that the website is down or cannot be used due to an error.  This group of people tend to have the strictest definition of what constitutes uptime because they are on the front line receiving the most feedback from the users.  If uptime were measured at the application level, uptimes would realistically be between 92-98%.

Differing definitions of uptime are neither right nor wrong.  The point is, organizations must come to an agreement of what constitutes downtime and decide on a realistic uptime goal for measurement.  Once monitoring begins, it will become apparent after a short time – one week – what the uptime is.  With that number, SLA agreements can be written with more detail and clarity.