Understanding the Application Health Score

Overview

When you log in to the NGINX Controller user interface, you will see the Analytics Dashboard Overview page. This page contains an Application Health Score (AHS) that reflects your application’s performance.

The AHS is a customizable Apdex-like numerical measure that can be used to estimate the quality of experience for your web application. It lets you configure service-level monitoring for your applications.

You can select any combination of the following three service-level indicators (SLI) to create your AHS:

  • Successful requests (selected by default),
  • (Optional) Request time (95th percentile), and
  • (Optional) NGINX Controller Agent availability.

Successful requests are determined according to the total observed average request time (P95) either below the low threshold (100% satisfying) or between the low and high threshold (partially satisfying).

A simplified formula for AHS is as follows:

AHS = (Successful Requests %) * (Timely Requests %) * (Agent Availability %)

When you select the Request Time (95th percentile) for inclusion in the AHS, you can set two thresholds for the total observed average request time (P95):

  • Low threshold for satisfying requests.
  • High threshold for partially satisfying requests.

If the average request time (P95) for the selected time period is below the low threshold, this is considered as a “100% satisfying” state of requests.

If the request time is above the low threshold and below the high threshold, a “satisfaction ratio” is calculated accordingly. Requests above the high threshold are considered to be “0%”, or “unsatisfying”.

For example: If the low threshold is 0.2s and the high threshold is 1s, a request time greater than 1s would be considered unsatisfying and the resulting score would be 0%.

The algorithm for calculating the AHS is as follows. Here, T1 represents the low threshold and T2 represents the high threshold.

successful_req_pct = (nginx.http.request.count - nginx.http.status.5xx) / nginx.http.request.count

if (nginx.http.request.time.pctl95 < T1)
   timely_req_pct = 1
else
   if (nginx.http.request.time.pctl95 < T2)
       timely_req_pct = 1 - (nginx.http.request.time.pctl95 - T1) / (T2 - T1)
   else
       timely_req_pct = 0

m1 = successful_req_pct
m2 = timely_req_pct
m3 = agent_up_pct

app_health_score = m1 * m2 * m3

Customize the Application Health Score

Take the steps below to customize the Application Health Score (AHS) that displays on the Overview page.

Note:
By default, the AHS and other metrics on the Overview page are calculated for all of the Instances monitored by the Controller Agent.
  1. Open the NGINX Controller user interface and log in.

  2. On the Overview page, select the Settings (gear) icon in the Application Health Score panel.

  3. In the Service Level Monitoring window, define the following:

    • (Optional) Create a custom name for the monitor (replaces “Application Health Score”).

    • (Optional) Select tags to narrow the data source(s) to a specific Instance or set of Instances.

    • Select the Service Indicators that you want to include in the score calculation.

      • Successful requests (selected by default).
      • Request time (95th percentile): Set a low threshold and a high threshold, in seconds.
      • Agent availability.
  4. Select Save.

What’s Next


This documentation applies to the following versions of NGINX Controller Documentation: 3.0, 3.1, 3.2, 3.3, 3.4, 3.5, 3.6, 3.7, 3.8, 3.9, 3.10, 3.11, 3.12, 3.13, 3.14, 3.15 and 3.16.