Azure Event Grid: Correct Syntax For --mi-user-assigned

Aug 20, 2025 by Kenji Nakamura 56 views

Hey guys! Ever wrestled with Azure Event Grid and user-assigned managed identities? It can be a bit tricky, but let's break it down and get it working. This article will walk you through the correct syntax for the --mi-user-assigned parameter when updating an Event Grid system topic using the Azure CLI. We'll cover common pitfalls and ensure you can seamlessly assign user-managed identities to your Event Grid resources. So, buckle up, and let’s dive into the world of Azure Event Grid!

Understanding Managed Identities in Azure

Before we jump into the syntax, let’s quickly recap managed identities. Managed identities allow your Azure services to securely access other Azure resources without embedding credentials in your code. Think of it as giving your services an Azure Active Directory (Azure AD) identity, making authentication a breeze. There are two types:

System-assigned: Tied to the lifecycle of the Azure resource.
User-assigned: Standalone Azure resources that can be assigned to multiple services.

We're focusing on user-assigned managed identities here because they offer more flexibility. You can share them across multiple resources and manage their permissions centrally. It is a good practice to understand this part before moving into the next one.

The Challenge: Updating Event Grid with User-Assigned Identity

The user in question was trying to update an Event Grid system topic to use a user-assigned managed identity. They were using the az eventgrid system-topic update command, which is the correct approach. However, they encountered a usage error when using the --mi-user-assigned parameter. The command they were attempting looked something like this:

az eventgrid system-topic update -n $eGridName -g $rgName --mi-user-assigned $identity.clientId

The issue lies in how the identity is being specified. The Azure CLI expects a specific format for this parameter, and simply passing the client ID might not cut it. So, what's the right way to do it? Let's find out.

The Correct Syntax for --mi-user-assigned

The --mi-user-assigned parameter requires the resource ID of the user-assigned managed identity. Not just the client ID, but the full resource ID. This ensures Azure can correctly identify and associate the identity with your Event Grid system topic.

Here's the breakdown of why this matters:

Clarity for Azure: The resource ID is the unique identifier for any Azure resource. It provides a complete path, including the subscription, resource group, and identity name.
Avoiding Ambiguity: Client IDs, while unique within a tenant, might not be globally unique. The resource ID eliminates any potential ambiguity.
Underlying API Requirements: The Azure Resource Manager (ARM) API, which the CLI uses under the hood, expects the resource ID for identity assignments.

So, how do you get the resource ID? There are a couple of ways:

1. Using the Azure CLI

The easiest way is to use the az identity show command. This command retrieves information about a managed identity, including its resource ID.

identityResourceId=$(az identity show -n <identity-name> -g <resource-group-name> --query id --output tsv)
echo $identityResourceId

Replace <identity-name> and <resource-group-name> with the actual name of your user-assigned identity and its resource group. The --query id part extracts just the resource ID, and --output tsv formats the output for easy use in scripts.

2. Using the Azure Portal

If you prefer a graphical interface, you can find the resource ID in the Azure Portal:

Navigate to your User-assigned managed identity resource.
In the Overview section, you'll see the Resource ID listed.

Putting It All Together: The Correct Command

Now that we know how to get the resource ID, let's construct the correct az eventgrid system-topic update command:

az eventgrid system-topic update -n $eGridName -g $rgName --mi-user-assigned $identityResourceId

Here, $identityResourceId is the variable we populated in the previous step using az identity show. This command tells Azure Event Grid to use the specified user-assigned managed identity for authentication. This is the most crucial step in understanding this specific case.

Example Scenario: Step-by-Step Guide

Let’s walk through a complete example to solidify your understanding. Imagine you have:

An Event Grid system topic named myEventGrid in the resource group myResourceGroup.
A user-assigned managed identity named myIdentity in the resource group myResourceGroup.

Here are the steps to assign the identity to the Event Grid topic:

Get the identity's resource ID:

identityResourceId=$(az identity show -n myIdentity -g myResourceGroup --query id --output tsv)
echo $identityResourceId

Update the Event Grid system topic:

az eventgrid system-topic update -n myEventGrid -g myResourceGroup --mi-user-assigned $identityResourceId

Verify the assignment:

You can verify the assignment in the Azure Portal by navigating to your Event Grid system topic, selecting Identity, and checking the User assigned tab. You should see your identity listed there. Alternatively, you can use the Azure CLI to view the Event Grid topic's properties:
```
az eventgrid system-topic show -n myEventGrid -g myResourceGroup --query identity
```
This command will output a JSON object containing the identity information, including the user-assigned identities.

Common Pitfalls and Troubleshooting Tips

Even with the correct syntax, things can sometimes go wrong. Here are some common pitfalls and how to troubleshoot them:

Incorrect Resource ID: Double-check that you have the correct resource ID for your user-assigned identity. A typo can lead to errors.
Permissions: Ensure the managed identity has the necessary permissions to access the resources you need. Event Grid might require specific roles, such as the