when to use system-assigned managed identities? when to use user-assigned managed identity

In Azure, Managed Identities are a way to securely provide credentials to Azure resources without storing sensitive information in your code or configuration files. There are two types of managed identities: system-assigned managed identities and user-assigned managed identities. The choice between these two depends on your specific use case and requirements.

System-Assigned Managed Identity:

1. Use Case:

   • Use system-assigned managed identities when the identity needs to be tied to the lifecycle of the Azure resource itself, such as an Azure Virtual Machine or an Azure App Service.

2. Lifecycle:

   • The system-assigned managed identity is created when you create the Azure resource, and it is deleted when the resource is deleted. It is directly associated with and managed by the Azure resource.

3. Simplicity:

   • It simplifies the management of identity because you don't need to create or delete it separately. The identity is provisioned and deprovisioned with the associated resource.

4. One-to-One Relationship:

   • Each system-assigned managed identity is unique to a single Azure resource.

User-Assigned Managed Identity:

1. Use Case:

   • Use user-assigned managed identities when you need to share an identity across multiple Azure resources or when you want to assign the identity to an existing resource.

2. Lifecycle:

   • User-assigned managed identities are created as standalone Azure resources. You create them independently of any Azure resource, and they persist even if the associated resources are deleted.

3. Flexibility:

   • It provides flexibility because you can assign a user-assigned managed identity to multiple Azure resources. This is useful in scenarios where you want to reuse the same identity across different resources.

4. Many-to-Many Relationship:

   • One user-assigned managed identity can be associated with multiple Azure resources, and multiple user-assigned managed identities can be associated with a single Azure resource.

Choosing Between Them:

• Resource Lifecycle:

  • If the identity's lifecycle is tightly coupled with the Azure resource, use a system-assigned managed identity.
  • If you need more flexibility and want to manage identities independently of the resource lifecycle, use user-assigned managed identities.

• Reuse Across Resources:

  • If you need to share an identity across multiple resources, use a user-assigned managed identity.
  • If the identity is specific to a single resource, a system-assigned managed identity may be sufficient.

• Granular Control:

  • If you want more granular control over the identity assignment process, consider using user-assigned managed identities.

In summary, choose system-assigned managed identities when the identity's lifecycle is tied to a specific Azure resource, and choose user-assigned managed identities when you need more flexibility and want to share the identity across multiple resources or manage it independently. The decision depends on the specific requirements and architecture of your Azure solution.