Our reporting was showing that our web app has 3 instances running on both an external report and in the Scale Out blade of the App Service. We only had 1 instance taking traffic/requests etc. Why is only 1 instance receiving requests?
Our reporting was showing that our web app has 3 instances running on both an external report and in the Scale Out blade of the App Service. We only had 1 instance taking traffic/requests etc. Why is only 1 instance receiving requests?
Likely the two other instances are unhealthy.
This can happen for a number of reasons such as High CPU / instance resource exhaustion.
To mitigate, you can try to-
Scale Out / In, By Scaling Out this will help to check if resource consumption is an issue and assign more resources to your app while also letting additional instances receive traffic for your app again. Then if you believe that your app should be within resource limits, by Scaling Back In the two instances which were causing issue may be replaced.
Scale Down / Up, This is another option to try and get new instances allocated for your app. However, note that if scaling to a new tier (i.e. from Standard to Premium) that this may change the IPs of your app.
More information on scaling can be found here.
For the future, consider enabling the Health Check feature, this will ping the instances hosting your app and if a response is not received then removes the instance from rotation: https://docs.microsoft.com/en-us/azure/app-service/monitor-instances-health-check
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