Azure App Configuration Feature Flags in Blazor WASM App: Performance Concerns and Optimization

Question

Azure App Configuration Feature Flags in Blazor WASM App: Performance Concerns and Optimization

NavarathinamJaisankar-3207 0

Dear Team,

The implementation of Azure App Configuration Feature Flags in a Blazor WASM application allows for displaying a maintenance page based on feature flag status. However, there is a concern regarding performance when calling the API for feature flags on every page navigation. it is working fine as expected but concern is cost when every page navigation calling API to check state of the feature flags.

The current setup involves checking the feature flags via API on each navigation, with a caching strategy set to refresh every 60 seconds. The question is whether this approach may lead to performance issues and what optimized solutions exist to efficiently manage feature flag updates while still being able to display a maintenance page to end users when needed.

Additionally, cost implications related to the Azure App Service and Azure App Configuration are noted, along with considerations for using Event Grid for push/pull notifications, which may introduce further costs.

Looking for guidance on best practices to optimize this feature flag implementation without compromising performance or incurring unnecessary costs.

Thanks,
Jai

Siva Nair 2,340 Reputation points Microsoft External Staff Moderator

2025-05-28T20:28:51.1866667+00:00
Hi NavarathinamJaisankar-3207,

Have a look on below steps-

Instead of calling the API on every navigation, cache the feature flags in the browser (e.g., localStorage or sessionStorage) with a timestamp. Only refresh if the cache is older than your TTL (60 seconds).
// Pseudo-code if (cacheExists && cacheIsFresh) useCachedFlags(); else fetchFlagsFromAPI();
This reduces API calls significantly while still keeping flags reasonably fresh.

Use Azure App Configuration’s Built-in Caching- If you're using the Azure SDK in your backend API, leverage the AzureAppConfigurationRefreshOptions to cache feature flags and only refresh them periodically or based on a sentinel key.

Sentinel Key: A special key that, when changed, triggers a refresh of all feature flags.

This avoids polling and allows manual control over when flags are refreshed.

If you need near real-time updates (e.g., instantly show a maintenance page), you can:

Use Azure Event Grid to notify your backend when a feature flag changes.

Backend updates a cache or database.

Blazor WASM app checks this intermediate store (e.g., Redis, Cosmos DB, or a lightweight API endpoint).

This avoids direct frequent calls to Azure App Configuration from the client.

Load feature flags once during app initialization and store them in memory or local storage. This is especially useful for flags like "maintenance mode" that don’t change often.

Instead of calling Azure App Configuration directly from the client, route all flag checks through a lightweight API that handles caching and refresh logic. This centralizes control and reduces client complexity.

Note-

Use client-side caching with a 60-second TTL.

Optionally, use a sentinel key to control refreshes.

Avoid Event Grid unless you need instantaneous updates.

Consider a backend API that handles caching and serves flags to the client.

Refer this link- https://learn.microsoft.com/en-us/azure/azure-app-configuration/howto-best-practices

https://learn.microsoft.com/en-us/azure/azure-app-configuration/manage-feature-flags

https://learn.microsoft.com/en-us/azure/azure-app-configuration/concept-feature-management

If you have any further assistant, do let me know.
Pravallika Kothaveeranna Gari 955 Reputation points Microsoft External Staff Moderator

2025-06-02T07:46:23.07+00:00

Hi @NavarathinamJaisankar-3207, Just checking in to see if the above provided information helped. If you have any further queries, do let us know
Harshitha Veeramalla 1,301 Reputation points Microsoft External Staff Moderator

2025-06-03T06:13:20.4033333+00:00

Hi @NavarathinamJaisankar-3207, just checking in to see if above information was helpful. If you have any further updates on this issue, please feel free to post back.

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Pravallika Kothaveeranna Gari 955 Reputation points Microsoft External Staff Moderator

2025-06-02T07:46:23.07+00:00

Hi @NavarathinamJaisankar-3207, Just checking in to see if the above provided information helped. If you have any further queries, do let us know
Harshitha Veeramalla 1,301 Reputation points Microsoft External Staff Moderator

2025-06-03T06:13:20.4033333+00:00

Hi @NavarathinamJaisankar-3207, just checking in to see if above information was helpful. If you have any further updates on this issue, please feel free to post back.

Answer 1

Hi @NavarathinamJaisankar-3207,

The question is whether this approach may lead to performance issues

Yes, it can lead to the performance issues.
Every time when the user navigates to a new page, the application tries to call the backend to check the feature flag status. Which results in the repeated API traffic, even if the flag value hasn't changed.
API and App Configuration consumption increases with each page views.

UI rendering will be delayed with each network call leading to high latency.

Increases load on backend services, affecting the app performance and scalability.

what optimized solutions exist to efficiently manage feature flag updates

Load the feature flag only once on App Initialization.

This works well if flags won't change frequently, else you will see a delay of 1 or 2 min.

Or else you can cache feature flag in backend using IMemoryCache mechanism.
When Blazor WASM clients request feature flags, the backend responds from the cache instead of querying Azure App Configuration each time.

This option Reduces Azure Load, Improves Performance, Minimizes Costs and Scales Better

Refer this MSDoc which explains how to Reduce requests made to App Configuration

Hope this helps

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Azure App Configuration Feature Flags in Blazor WASM App: Performance Concerns and Optimization

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