What Is Apdex and How Can It Help Monitor App Health?

February 16, 2021 Scott Rogers

VMware recently announced that Apdex is now available in Tanzu Observability by Wavefront. Users can access it by selecting Apdex when viewing the application status page. 

What is Apdex?

Apdex is a “numerical measure of user satisfaction with the performance of enterprise applications," according to the Apdex Alliance website. Similar to how request, error, and duration (RED) metrics measure the health of a service, we can use Apdex to score response time based upon a self-defined target. Apdex can express this health score across disparate applications and services in a consistent, or normalized, way.

How does it work?

Calculating Apdex is simple and requires just three steps:

Step 1: Set a threshold (T) value indicating the desired or accepted response time for the service. 

Step 2: Count and group actual responses into three buckets:

  • Happy < T-value

  • Tolerating > T-value and < 4x T-value

  • Frustrated > 4x T-value

Step 3: Using the buckets, calculate the Apdex score like so:

  • Apdex = ( Happy + ( 1/2 Tolerating) ) / Total responses

The result is a score between 1 and 0, where one (1) indicates all responses were less than or equal to the T-value. The Apdex Alliance suggests a rating scale where:

  • Excellent > .94

  • Good > .85

  • Fair > .7

  • Poor > .5

  • Unacceptable <= .5

How can it help?

I'll draw from my own experience to answer this question. I used to lead IT service management for a large, U.S.-based company that operated several highly trafficked websites. We used response time as an analog for customer satisfaction. But while using response time made good sense, leadership wanted a single score shown as a stoplight. This situation presented a challenge because we never quite agreed on how to translate response times into a single red/yellow/green score. It seems we were always making changes to accommodate different ideas.

Apdex to the rescue!

Apdex would have been a great solution to this challenge. A single score with a defined scale is easy to explain. Apdex also helps standardize quality reporting for different services by setting the T-value, which anyone can easily understand.

How do you get started with Apdex?

Apdex is easy to calculate, and many tools will do it for you, including Tanzu Observability, which shows Apdex for services alongside the SRE RED metrics. Together, this provides a comprehensive view of service quality. Take a look at Apdex, as you will likely find that it is yet another excellent tool to help understand the quality of your services.

Visit the Tanzu Observability page to sign up for a free trial and start using Apdex for your microservices today!


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