Table of Contents
Why does my app fail to retrieve Key Vault secrets through App Configuration?
Troubleshoot runtime failures when retrieving Azure Key Vault secrets through App Configuration. Learn why a missing managed identity access policy or RBAC role is the most likely cause and how to configure the correct permissions for secure access.
Question
You are deploying an application that retrieves secrets from Azure Key Vault through App Configuration. The application fails to retrieve secrets at runtime. What could be the most likely cause?
A. The application is not assigned the correct Azure Key Vault access policy
B. The secret values are too large to be stored in Key Vault
C. The App Configuration service does not support Key Vault references
D. The application is using environment variables instead of App Configuration
Answer
A. The application is not assigned the correct Azure Key Vault access policy
Explanation
If the application lacks the necessary access policy or managed identity permissions in Azure Key Vault, it will fail to retrieve secrets at runtime. Ensuring proper role assignments and permissions is crucial. For more information, please refer to the “Secure app configuration data by using App Configuration or Azure Key Vault – Demo” lecture.
When an application uses Azure App Configuration to resolve Key Vault references, a two-step authentication process occurs. First, the application authenticates to the App Configuration store. Second, the App Configuration service itself must authenticate to the target Azure Key Vault to retrieve the secret’s value. The most frequent point of failure in this chain is the second step, which is an authorization problem between App Configuration and Key Vault.
Cause of Failure: Missing Permissions
For App Configuration to access a Key Vault, its managed identity (either system-assigned or user-assigned) must be granted permission on the Key Vault. If this permission is missing or incorrect, the App Configuration service will be unable to resolve the secret reference, leading to a runtime failure in the application.
The required permission can be granted in one of two ways:
- Key Vault Access Policy: Creating an access policy on the Key Vault that grants the App Configuration’s managed identity Get and List permissions for secrets.
- Azure Role-Based Access Control (RBAC): Assigning the App Configuration’s managed identity the Key Vault Secrets User role at the scope of the Key Vault.
A failure to configure either of these permissions correctly is the most common reason an application can connect to App Configuration but still fails to retrieve the final secret value.
Analysis of Incorrect Options
B. The secret values are too large to be stored in Key Vault. While secrets in Key Vault have a size limit of 25 kB, this is an unlikely root cause for a general failure to retrieve secrets. A permission issue is a far more common configuration error.
C. The App Configuration service does not support Key Vault references. This statement is factually incorrect. The ability to reference Key Vault secrets is a core feature of the Azure App Configuration service, designed to separate configuration from secrets.
D. The application is using environment variables instead of App Configuration. This describes a different application design. If the application is coded to use App Configuration for its settings, it would not be using environment variables for the same configuration values. This does not explain why the App Configuration retrieval process itself is failing.
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