Azure App Service quotas and metrics
Azure App Service provides built-in monitoring functionality for web, mobile, and API apps in the Azure portal.
In the portal, you can review quotas and metrics for an app and App Service plan. You can set up alerts and autoscaling rules based on metrics.
Quotas
Apps that are hosted in App Service are subject to certain limits on the resources that they can use. The App Service plan that's associated with the app defines the limits.
Note
App Service Free and Shared (preview) service plans are base tiers that run on the same Azure virtual machines as other App Service apps. Some apps might belong to other customers. These tiers are intended only for development and testing purposes.
If the app is hosted in a Free or Shared plan, quotas define the limits on the resources that the app can use. Quotas for apps in a Free or Shared plan are:
| Quota | Description |
|---|---|
| CPU (Short) | The amount of CPU allowed for this app in a five-minute interval. This quota resets every five minutes. |
| CPU (Day) | The total amount of CPU allowed for this app in a day. This quota resets every 24 hours at midnight UTC. |
| Memory | The total amount of memory allowed for this app. |
| Bandwidth | The total amount of outgoing bandwidth allowed for this app in a day. This quota resets every 24 hours at midnight UTC. |
| Filesystem | The total amount of storage allowed. |
If the app is hosted in a Basic, Standard, or Premium plan, the limits on the resources that it can use are set by the size (small, medium, large) and instance count (1, 2, 3, and so on) of the App Service plan. The only quota applicable to apps that are hosted in a Basic, Standard, or Premium plan is Filesystem.
For more information about the specific quotas, limits, and features available to the App Service tiers, see Azure App Service limits.
Quota enforcement
If an app exceeds the CPU (Short), CPU (Day), or Bandwidth quota, the app is stopped until the quota resets. During this time, all incoming requests result in an HTTP 403 error.
If the app exceeds its Memory quota, it's stopped temporarily.
If app exceeds the Filesystem quota, any write operation fails. Write operation failures include any writes to logs.
You can increase or remove quotas from your app by upgrading your App Service plan.
Metrics
Metrics provide information about the app's or the App Service plan's behavior. App Service plan metrics are available only for plans in Basic, Standard, Premium, and Isolated tiers.
For a list of available metrics for apps or for App Service plans, see Supported metrics for Microsoft.Web.
Note
Metrics for an app include the requests to the app's Source Control Manager (SCM) site, also known as Kudu. This includes requests to view the site's log stream by using Kudu. Log-stream requests might span several minutes, which will affect the Request Time metrics. Be aware of this relationship when you're using these metrics with autoscale logic.
HTTP Server Errors records only requests that reach the back-end service (the workers that host the app). If the requests are failing at the front end, they're not recorded as HTTP server errors. You can use the health check feature and Application Insights availability tests for outside-in monitoring.
CPU time vs. CPU percentage
Two metrics reflect CPU usage:
CPU Time: Useful for apps hosted in Free or Shared plans, because one of their quotas is defined in CPU minutes that the app uses.
CPU Percentage: Useful for apps hosted in Basic, Standard, and Premium plans, because they can be scaled out. CPU percentage is a good indication of the overall usage across instances.
Retention policy
The service logs and aggregates metrics for an app and for an App Service plan. The metrics are retained according to these rules.
Monitoring quotas and metrics in the Azure portal
To review the status of the quotas and metrics that affect an app, go to the Azure portal.
To find quotas, select Settings > Quotas. On each chart, you can review this information about the quota:
- Name
- Reset interval
- Current limit
- Current value
You can access metrics directly from the resource Overview page. This page shows charts that represent some of the app metrics. Selecting any of those charts takes you to the Metrics view, where you can create custom charts, query various metrics, and much more.
To learn more about metrics, see Azure Monitor data platform.
Alerts and autoscale
Metrics for an app or an App Service plan can be connected to alerts. For more information, see Alerts.
Apps hosted in Basic or higher App Service plans support autoscale. With autoscale, you can configure rules that monitor the App Service plan metrics. Rules can increase or decrease the instance count, which can provide additional resources as needed. Rules can also help you save money when the app is overprovisioned.
For more information about autoscale, see Get started with autoscale in Azure and Best practices for autoscale.