Merge pull request #220683 from zhenlan/faq

Add an FAQ about how to estimate requests sent to AppConfig

Author: 19BMG00

articles/azure-app-configuration/faq.yml

@@ -52,13 +52,13 @@ sections:
         answer: |
           There's a limit of 10 KB for a single key-value, including attributes such as label, content-type, tags, and other metadata.
 
-          This limit should be sufficient for a single setting in most applications. If you find that your setting is larger than this limit, you may consider storing your data elsewhere and [add a reference of that data](./howto-best-practices.md#references-to-external-data) in App Configuration.
+          This limit should be sufficient for a single setting in most applications. If you find that your setting is larger than this limit, you may consider storing your data elsewhere, and [add a reference of that data](./howto-best-practices.md#references-to-external-data) in App Configuration.
 
       - question: How should I store configurations for multiple environments (test, staging, production, and so on)?
         answer: |
           You control who can access App Configuration at a per-store level. Use a separate store for each environment that requires different permissions. This approach provides the best security isolation.
           
-          If you do not need security isolation between environments, you can use labels to differentiate between configuration values. [Use labels to enable different configurations for different environments](./howto-labels-aspnet-core.md) provides a complete example.
+          If you don't need security isolation between environments, you can use labels to differentiate between configuration values. [Use labels to enable different configurations for different environments](./howto-labels-aspnet-core.md) provides a complete example.
           
       - question: What are the recommended ways to use App Configuration?
         answer: |
@@ -109,14 +109,14 @@ sections:
           Azure App Configuration supports Azure availability zones to protect your application and data from single datacenter failures. All availability zone enabled regions consist of a minimum of 3 availability zones, where each is a physically independent datacenter. For resiliency, this support in App Configuration is enabled for all customers at no extra cost. Following are regions that App Configuration has enabled availability zone support. For more information, see [Regions and Availability Zones in Azure.](../reliability/availability-zones-service-support.md)
           
           [!INCLUDE [Azure App Configuration availability zones table](../../includes/azure-app-configuration-availability-zones.md)]
-          
+
       - question: Are there any limits on the number of requests made to App Configuration?
         answer: |
           Configuration stores in the Free tier are limited to 1,000 requests per day. Configuration stores in the Standard tier may experience temporary throttling when the request rate exceeds 30,000 requests per hour.
           
           When a store reaches its limit in the standard tier, it may return HTTP status code 429 for some requests made until the end of the hour. The `retry-after-ms` header in the response gives a suggested wait time (in milliseconds) before retrying the request.
           
-          If your application regularly experiences HTTP status code 429 responses, consider redesigning it to reduce the number of requests made. For more information, see [Reduce requests made to App Configuration](./howto-best-practices.md#reduce-requests-made-to-app-configuration)
+          If your application regularly experiences HTTP status code 429 responses, consider redesigning it to reduce the number of requests made. For more information, see [how to reduce requests made to App Configuration](./howto-best-practices.md#reduce-requests-made-to-app-configuration).
           
       - question: My application receives HTTP status code 429 responses. Why?
         answer: |
@@ -132,13 +132,23 @@ sections:
           
           †A configuration store may experience momentary throttling if it receives a large burst of requests. App Configuration clients, such as the Azure SDK, configuration provider libraries, and Azure Pipeline tasks, automatically retry on throttled requests. For any applications using one of these clients, or a custom client that retries on throttled requests, this momentary throttling should go unnoticed, should it occur.
 
+      - question: How do I estimate the number of requests my application may send to App Configuration?
+        answer: |
+          Let's take an example and assume you have an application with 1,000 configuration settings. Your application loads all those settings from App Configuration upon startup. After that, it checks for a sentinel key for configuration changes every 30 seconds. Whether you are running on Kubernetes, App Service, or VMs, let's assume you have 50 instances of your application running simultaneously.
+
+          Firstly, let's estimate the requests for configuration monitoring. Each instance of your application will send one request for the sentinel key to App Configuration every 30 seconds, so it will send 120 (=3600/30) requests in an hour. Given you have 50 instances of your application, your application sends 6,000 (=120x50) total requests every hour for configuration monitoring.
+
+          Secondly, let's estimate the requests for configuration loading/reloading. Your application loads all settings at the startup or whenever a sentinel key change is detected. Each request to App Configuration can retrieve up to 100 key-values, so it will take 10 (=1000/100) requests to load all settings. Given you have 50 application instances, you send 500 (=10x50) total requests when your application restarts or reloads its configuration.
+
+          Finally, let's put it together. Assuming you updated the sentinel key twice within an hour, your App Configuration store will thus receive 7,000 (=6,000+500x2) total requests for that hour. Update the numbers in this example to match your specific setup and design accordingly so you have a sufficient buffer against the hourly throttling limit. For more information, see [how to reduce requests made to App Configuration](./howto-best-practices.md#reduce-requests-made-to-app-configuration).
+          
       - question: Why can't I create an App Configuration store with the same name as one that I just deleted?
         answer: |
           All App Configuration stores in the standard tier have automatically enabled the [soft-delete](concept-soft-delete.md) feature. When a standard tier App Configuration store is deleted, its name is reserved for the retention period. To recreate a store with the same name before the retention period expires, you need to [purge the soft-deleted store](howto-recover-deleted-stores-in-azure-app-configuration.md#list-recover-or-purge-a-soft-deleted-app-configuration-store) first, provided the store doesn't have purge protection enabled. If the purge protection is enabled, you must wait for the retention period to elapse. Use the purge function or set a shorter retention period if you often need to recreate a store with the same name.
 
       - question: How can I restore an App Configuration store that I deleted mistakenly?
         answer: |
-          All App Configuration stores in the standard tier support the [soft-delete](concept-soft-delete.md) feature, which cannot be disabled. You can recover a deleted store within its retention period. Follow these [instructions](howto-recover-deleted-stores-in-azure-app-configuration.md) to recover a mistakenly deleted App Configuration store.
+          All App Configuration stores in the standard tier support the [soft-delete](concept-soft-delete.md) feature, which can't be disabled. You can recover a deleted store within its retention period. Follow these [instructions](howto-recover-deleted-stores-in-azure-app-configuration.md) to recover a mistakenly deleted App Configuration store.
 
       - question: Can I create and update feature flags or Key Vault references programmatically?
         answer: |
@@ -150,7 +160,7 @@ sections:
         answer: |
           Spring profiles provide a way to separate parts of your application, including configuration, and make it only available in certain environments or when specific libraries are used.
 
-          You are recommended to set the label of your key-values to match your Spring profiles. By default, the App Configuration Spring provider library will load the key-values with the label(s) matching the current active Spring profile(s) (`${spring.profiles.active}`) if the label filter isn't set explicitly. If there is no active Spring profile set, key-values with "no label" will be loaded.
+          You're recommended to set the label of your key-values to match your Spring profiles. By default, the App Configuration Spring provider library will load the key-values with the label(s) matching the current active Spring profile(s) (`${spring.profiles.active}`) if the label filter isn't set explicitly. If there's no active Spring profile set, key-values with "no label" will be loaded.
 
           For example, with profiles `dev` and `prod`, you create key-values accordingly with the following labels.
 
@@ -167,7 +177,7 @@ sections:
           spring.cloud.azure.appconfiguration.stores[0].selects[0].label-filter: my-label
           ```
           
-          To select other labels and your Spring profile(s), you can use selects like `',${spring.profiles.active}'` which will select all keys without a label and the ones matching your Spring profiles. The rightmost label(s) take priority when duplicate keys are found.
+          To select other labels and your Spring profile(s), you can use a label filter like `',${spring.profiles.active}'`, which will select all keys without a label and the ones matching your Spring profiles. The rightmost label(s) take priority when duplicate keys are found.
 
       - question: How can I receive announcements on new releases and other information related to App Configuration?
         answer: |