Azure App Service Plan metrics vs Azure Web App Metrics 'Data Out' Metric

Question

Azure App Service Plan metrics vs Azure Web App Metrics 'Data Out' Metric

Mora 0

Looking for insight on how App Plan metrics work in relation to the underlying instance(s).

For example, 'Data Out' is a metric on both sides, originally I thought that the app service plan would simply aggregate the data from the instances, but I see lower numbers in general. On a single instance and plan, the web app for example might show 50GB data out for the day, but the plan its hosted on metrics shows no more than 150MB (under the same aggregations/timeframe/etc). What is 'Data Out' tracking specifically on each side?

Praneeth Maddali 2,715 Reputation points Microsoft External Staff Moderator

2025-11-06T22:02:33.1166667+00:00

Hi @Mora

I'm just reaching out to see if your issue has been resolved or if you've had a chance to review my previous comment?
Vimal Lalani 2,400 Reputation points Microsoft External Staff Moderator

2025-12-10T22:52:09.99+00:00
Hi @Mora

These two metrics are measured at different layers, so the numbers do not match.

Web App → Data Out (per app)

This shows the total outbound data sent by your specific web app, including HTTP/S responses, WebSocket data, File downloads, API responses

This is measured after your app processes the request, so it usually shows higher data usage.

App Service Plan → Data Out

This shows network data leaving the App Service VM, but it does not include all the data counted at the app level. It includes VM-level outbound traffic and does not include most client traffic handled by front-end.

It often counts infrastructure-level traffic, not per-app HTTP responses. A large part of your Web App’s outbound traffic is handled through the front-end load balancer, not the VM directly. So the App Service Plan “Data Out” metric usually stays much lower.

This is expected and normal. I hope this information helps address your query.
Vimal Lalani 2,400 Reputation points Microsoft External Staff Moderator

2025-12-12T01:00:39.5066667+00:00

Hi @Mora

Just following up to see if the above information was helpful. Feel free to post back if you need any further assistance.

1 answer

Your answer

Praneeth Maddali 2,715 Reputation points Microsoft External Staff Moderator

2025-11-06T22:02:33.1166667+00:00

Hi @Mora

I'm just reaching out to see if your issue has been resolved or if you've had a chance to review my previous comment?
Vimal Lalani 2,400 Reputation points Microsoft External Staff Moderator

2025-12-10T22:52:09.99+00:00

Hi @Mora

These two metrics are measured at different layers, so the numbers do not match.

Web App → Data Out (per app)

This shows the total outbound data sent by your specific web app, including HTTP/S responses, WebSocket data, File downloads, API responses

This is measured after your app processes the request, so it usually shows higher data usage.

App Service Plan → Data Out

This shows network data leaving the App Service VM, but it does not include all the data counted at the app level. It includes VM-level outbound traffic and does not include most client traffic handled by front-end.

It often counts infrastructure-level traffic, not per-app HTTP responses. A large part of your Web App’s outbound traffic is handled through the front-end load balancer, not the VM directly. So the App Service Plan “Data Out” metric usually stays much lower.

This is expected and normal. I hope this information helps address your query.
Vimal Lalani 2,400 Reputation points Microsoft External Staff Moderator

2025-12-12T01:00:39.5066667+00:00

Hi @Mora

Just following up to see if the above information was helpful. Feel free to post back if you need any further assistance.

Answer 1

Hi @Mora

This difference happens because the 'Data Out' metric is calculated in various ways in the Azure Portal based on context and default settings, rather than due to any limitation of the App Service Plan in displaying total volume.

Web App "Data Out"

Tracks the total outbound bytes sent by your app, including HTTP responses, API calls, and file downloads.
Uses Total (Sum) as the default aggregation, displaying the cumulative volume (e.g., 50 GB).
Provides accurate data for app-specific traffic and billing purposes.

App Service Plan "Data Out"

Measures outbound bandwidth at the VM infrastructure level across all instances.
Offers both Total and Average aggregations:
Total shows the full sum across all instances (matches Web App in single-instance scenarios).
Average displays bytes per instance per time interval (often the default chart view).
The metric description mentions "average" because it's the default view, but you can switch to Total.

Why You See 50 GB vs 150 MB

The Web App metric uses Total aggregation, resulting in 50 GB.
The App Service Plan metric likely uses Average aggregation, showing about 150 MB per 1-minute sample.
Switching the Plan metric to Total should display around 50 GB, with minor differences due to overhead.

Actionable Advice

In Azure Portal Metrics:

Navigate to the metrics for both the Web App and the App Service Plan.
Ensure that Aggregation is set to Total (Sum) for each.
Review and compare the results side by side.

Please utilize Web App 'Data Out' (Total) for the following purposes:

Obtaining precise application traffic volume
Estimating billing amounts
Receiving alerts regarding application behavior

Please utilize Plan 'Data Out' (Total) for the following purposes:

Aggregating egress data across applications
Conducting capacity planning

Please ensure that you do not compare Total (Web App) with Average (Plan); it is important to consistently align aggregation types for accurate analysis.

Reference:

https://dori-uw-1.kuma-moon.com/en-us/azure/azure-monitor/reference/supported-metrics/microsoft-web-sites-metrics#bytes-sent

https://dori-uw-1.kuma-moon.com/en-us/azure/azure-monitor/reference/supported-metrics/microsoft-web-serverfarms-metrics#bytes-sent

https://dori-uw-1.kuma-moon.com/en-us/azure/azure-monitor/metrics/metrics-aggregation-explained

Let us know if the above helps or you need further assistance on this issue.

Please "upvote" if the information helped you. This will help us and others in the community as well.

Mora 0 Reputation points

2025-12-10T21:57:55.54+00:00

Hi thanks for checking on this but this did not help. The metrics were both set to 'Data Out' and both set to the same time granularity and aggregation (Sum) as indicated originally. I double checked just now and can confirm that in a service plan with a single instance, the service plan shows much, much less data out.

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Azure App Service Plan metrics vs Azure Web App Metrics 'Data Out' Metric

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