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How to use managed identities with Azure Container Instances

  • บทความ

Use managed identities for Azure resources to run code in Azure Container Instances that interacts with other Azure services - without maintaining any secrets or credentials in code. The feature provides an Azure Container Instances deployment with an automatically managed identity in Microsoft Entra ID.

In this article, you learn more about managed identities in Azure Container Instances and:

  • Enable a user-assigned or system-assigned identity in a container group
  • Grant the identity access to an Azure key vault
  • Use the managed identity to access a key vault from a running container

Adapt the examples to enable and use identities in Azure Container Instances to access other Azure services. These examples are interactive. However, in practice your container images would run code to access Azure services.

Why use a managed identity?

Use a managed identity in a running container to authenticate to any service that supports Microsoft Entra authentication without managing credentials in your container code. For services that don't support AD authentication, you can store secrets in an Azure key vault and use the managed identity to access the key vault to retrieve credentials. For more information about using a managed identity, see What is managed identities for Azure resources?

Enable a managed identity

When you create a container group, enable one or more managed identities by setting a ContainerGroupIdentity property. You can also enable or update managed identities after a container group is running - either action causes the container group to restart. To set the identities on a new or existing container group, use the Azure CLI, a Resource Manager template, a YAML file, or another Azure tool.

Azure Container Instances supports both types of managed Azure identities: user-assigned and system-assigned. On a container group, you can enable a system-assigned identity, one or more user-assigned identities, or both types of identities. If you're unfamiliar with managed identities for Azure resources, see the overview.

Use a managed identity

To use a managed identity, the identity must be granted access to one or more Azure service resources (such as a web app, a key vault, or a storage account) in the subscription. Using a managed identity in a running container is similar to using an identity in an Azure Virtual Machine (VM). See the VM guidance for using a token, Azure PowerShell or Azure CLI, or the Azure SDKs.

Prerequisites

  • This article requires version 2.0.49 or later of the Azure CLI. If using Azure Cloud Shell, the latest version is already installed.

Create an Azure key vault

The examples in this article use a managed identity in Azure Container Instances to access an Azure key vault secret.

First, create a resource group named myResourceGroup in the eastus location with the following az group create command:

az group create --name myResourceGroup --location eastus

Use the az keyvault create command to create a key vault. Be sure to specify a unique key vault name.

az keyvault create \
  --name mykeyvault \
  --resource-group myResourceGroup \
  --location eastus

Store a sample secret in the key vault using the az keyvault secret set command:

az keyvault secret set \
  --name SampleSecret \
  --value "Hello Container Instances" \
  --description ACIsecret --vault-name mykeyvault

Continue with the following examples to access the key vault using either a user-assigned or system-assigned managed identity in Azure Container Instances.

Example 1: Use a user-assigned identity to access Azure key vault

Create an identity

First create an identity in your subscription using the az identity create command. You can use the same resource group used to create the key vault, or use a different one.

az identity create \
  --resource-group myResourceGroup \
  --name myACIId

To use the identity in the following steps, use the az identity show command to store the identity's service principal ID and resource ID in variables.

# Get service principal ID of the user-assigned identity
SP_ID=$(az identity show \
  --resource-group myResourceGroup \
  --name myACIId \
  --query principalId --output tsv)

# Get resource ID of the user-assigned identity
RESOURCE_ID=$(az identity show \
  --resource-group myResourceGroup \
  --name myACIId \
  --query id --output tsv)

Grant user-assigned identity access to the key vault

Run the following az keyvault set-policy command to set an access policy on the key vault. The following example allows the user-assigned identity to get secrets from the key vault:

 az keyvault set-policy \
    --name mykeyvault \
    --resource-group myResourceGroup \
    --object-id $SP_ID \
    --secret-permissions get

Enable user-assigned identity on a container group

Run the following az container create command to create a container instance based on Microsoft's azure-cli image. This example provides a single-container group that you can use interactively to run the Azure CLI to access other Azure services. In this section, only the base operating system is used. For an example to use the Azure CLI in the container, see Enable system-assigned identity on a container group.

The --assign-identity parameter passes your user-assigned managed identity to the group. The long-running command keeps the container running. This example uses the same resource group used to create the key vault, but you could specify a different one.

az container create \
  --resource-group myResourceGroup \
  --name mycontainer \
  --image mcr.microsoft.com/azure-cli \
  --assign-identity $RESOURCE_ID \
  --command-line "tail -f /dev/null"

Within a few seconds, you should get a response from the Azure CLI indicating that the deployment completed. Check its status with the az container show command.

az container show \
  --resource-group myResourceGroup \
  --name mycontainer

The identity section in the output looks similar to the following, showing the identity is set in the container group. The principalID under userAssignedIdentities is the service principal of the identity you created in Microsoft Entra ID:

[...]
"identity": {
    "principalId": "null",
    "tenantId": "aaaabbbb-0000-cccc-1111-dddd2222eeee",
    "type": "UserAssigned",
    "userAssignedIdentities": {
      "/subscriptions/aaaa0a0a-bb1b-cc2c-dd3d-eeeeee4e4e4e/resourcegroups/danlep1018/providers/Microsoft.ManagedIdentity/userAssignedIdentities/myACIId": {
        "clientId": "00001111-aaaa-2222-bbbb-3333cccc4444",
        "principalId": "aaaaaaaa-bbbb-cccc-1111-222222222222"
      }
    }
  },
[...]

Use user-assigned identity to get secret from key vault

Now you can use the managed identity within the running container instance to access the key vault. First launch a bash shell in the container:

az container exec \
  --resource-group myResourceGroup \
  --name mycontainer \
  --exec-command "/bin/bash"

Run the following commands in the bash shell in the container. To get an access token to use Microsoft Entra ID to authenticate to key vault, run the following command:

client_id="00001111-aaaa-2222-bbbb-3333cccc4444"
curl "http://169.254.169.254/metadata/identity/oauth2/token?api-version=2018-02-01&resource=https%3A%2F%2Fvault.azure.net&client_id=$client_id" -H Metadata:true -s

Output:

{"access_token":"xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx1QiLCJhbGciOiJSUzI1NiIsIng1dCI6Imk2bEdrM0ZaenhSY1ViMkMzbkVRN3N5SEpsWSIsImtpZCI6Imk2bEdrM0ZaenhSY1ViMkMzbkVRN3N5SEpsWSJ9......xxxxxxxxxxxxxxxxx","refresh_token":"","expires_in":"28799","expires_on":"1539927532","not_before":"1539898432","resource":"https://vault.azure.net/","token_type":"Bearer"}

To store the access token in a variable to use in subsequent commands to authenticate, run the following command:

TOKEN=$(curl 'http://169.254.169.254/metadata/identity/oauth2/token?api-version=2018-02-01&resource=https%3A%2F%2Fvault.azure.net' -H Metadata:true | jq -r '.access_token')

Now use the access token to authenticate to key vault and read a secret. Be sure to substitute the name of your key vault in the URL (https://mykeyvault.vault.azure.net/...):

curl https://mykeyvault.vault.azure.net/secrets/SampleSecret/?api-version=7.4 -H "Authorization: Bearer $TOKEN"

The response looks similar to the following, showing the secret. In your code, you would parse this output to obtain the secret. Then, use the secret in a subsequent operation to access another Azure resource.

{"value":"Hello Container Instances","contentType":"ACIsecret","id":"https://mykeyvault.vault.azure.net/secrets/SampleSecret/xxxxxxxxxxxxxxxxxxxx","attributes":{"enabled":true,"created":1539965967,"updated":1539965967,"recoveryLevel":"Purgeable"},"tags":{"file-encoding":"utf-8"}}

Example 2: Use a system-assigned identity to access Azure key vault

Enable system-assigned identity on a container group

Run the following az container create command to create a container instance based on Microsoft's azure-cli image. This example provides a single-container group that you can use interactively to run the Azure CLI to access other Azure services.

The --assign-identity parameter with no additional value enables a system-assigned managed identity on the group. The identity is scoped to the resource group of the container group. The long-running command keeps the container running. This example uses the same resource group used to create the key vault, which is in the scope of the identity.

# Get the resource ID of the resource group
RG_ID=$(az group show --name myResourceGroup --query id --output tsv)

# Create container group with system-managed identity
az container create \
  --resource-group myResourceGroup \
  --name mycontainer \
  --image mcr.microsoft.com/azure-cli \
  --assign-identity --scope $RG_ID \
  --command-line "tail -f /dev/null"

Within a few seconds, you should get a response from the Azure CLI indicating that the deployment completed. Check its status with the az container show command.

az container show \
  --resource-group myResourceGroup \
  --name mycontainer

The identity section in the output looks similar to the following, showing that a system-assigned identity is created in Microsoft Entra ID:

[...]
"identity": {
    "principalId": "bbbbbbbb-cccc-dddd-2222-333333333333",
    "tenantId": "aaaabbbb-0000-cccc-1111-dddd2222eeee",
    "type": "SystemAssigned",
    "userAssignedIdentities": null
},
[...]

Set a variable to the value of principalId (the service principal ID) of the identity, to use in later steps.

SP_ID=$(az container show \
  --resource-group myResourceGroup \
  --name mycontainer \
  --query identity.principalId --out tsv)

Grant container group access to the key vault

Run the following az keyvault set-policy command to set an access policy on the key vault. The following example allows the system-managed identity to get secrets from the key vault:

 az keyvault set-policy \
   --name mykeyvault \
   --resource-group myResourceGroup \
   --object-id $SP_ID \
   --secret-permissions get

Use container group identity to get secret from key vault

Now you can use the managed identity to access the key vault within the running container instance. First launch a bash shell in the container:

az container exec \
  --resource-group myResourceGroup \
  --name mycontainer \
  --exec-command "/bin/bash"

Run the following commands in the bash shell in the container. First, sign in to the Azure CLI using the managed identity:

az login --identity

From the running container, retrieve the secret from the key vault:

az keyvault secret show \
  --name SampleSecret \
  --vault-name mykeyvault --query value

The value of the secret is retrieved:

"Hello Container Instances"

Enable managed identity using Resource Manager template

To enable a managed identity in a container group using a Resource Manager template, set the identity property of the Microsoft.ContainerInstance/containerGroups object with a ContainerGroupIdentity object. The following snippets show the identity property configured for different scenarios. See the Resource Manager template reference. Specify a minimum apiVersion of 2018-10-01.

User-assigned identity

A user-assigned identity is a resource ID of the form:

"/subscriptions/{subscriptionId}/resourceGroups/{resourceGroupName}/providers/Microsoft.ManagedIdentity/userAssignedIdentities/{identityName}"

You can enable one or more user-assigned identities.

"identity": {
    "type": "UserAssigned",
    "userAssignedIdentities": {
        "myResourceID1": {
            }
        }
    }

System-assigned identity

"identity": {
    "type": "SystemAssigned"
    }

System- and user-assigned identities

On a container group, you can enable both a system-assigned identity and one or more user-assigned identities.

"identity": {
    "type": "SystemAssigned, UserAssigned",
    "userAssignedIdentities": {
        "myResourceID1": {
            }
        }
    }
...

Enable managed identity using YAML file

To enable a managed identity in a container group deployed using a YAML file, include the following YAML. Specify a minimum apiVersion of 2018-10-01.

User-assigned identity

A user-assigned identity is a resource ID of the form

'/subscriptions/{subscriptionId}/resourceGroups/{resourceGroupName}/providers/Microsoft.ManagedIdentity/userAssignedIdentities/{identityName}'

You can enable one or more user-assigned identities.

identity:
  type: UserAssigned
  userAssignedIdentities:
    {'myResourceID1':{}}

System-assigned identity

identity:
  type: SystemAssigned

System- and user-assigned identities

On a container group, you can enable both a system-assigned identity and one or more user-assigned identities.

identity:
  type: SystemAssigned, UserAssigned
  userAssignedIdentities:
   {'myResourceID1':{}}

Managed Identity on Windows containers

Managed Identity on Windows container groups works differently than Linux container groups. For Windows containers, metadata server (169.254.169.254) is not available for getting the Microsoft Entra ID token. Customers can follow a different pattern to get the access token in Windows containers. The pattern involves sending token request to the IDENTITY_ENDPOINT along with additional information such as principal id and secret as shown below. The IDENTITY_ENDPOINT and IDENTITY_HEADER are injected as environmental variable in your container.

curl -G -v %IDENTITY_ENDPOINT% --data-urlencode resource=https://vault.azure.net --data-urlencode principalId=<principal id> -H secret:%IDENTITY_HEADER%

A sample powershell script

identityEndpoint = $env:IDENTITY_ENDPOINT
$identityHeader = $env:IDENTITY_HEADER
$resource = "https://vault.azure.net"
$principalId = "b2ee9347-623c-4794-85af-2d5261356f67"
 
Invoke-RestMethod -Uri "$identityEndpoint" `
    -Method Get `
    -Headers @{secret = $identityHeader} `
    -Body @{resource = $resource; principalId = $principalId} `
    -ContentType "application/x-www-form-urlencoded"

Az Login module and other client libraries which depend on metadata server (169.254.169.254) will not work in a Windows Container. Additionally, Windows containers in vNet won't be able to connect to the endpoint; hence, a managed identity token can't be generated in a Windows virtual network container.

Next steps

In this article, you learned about managed identities in Azure Container Instances and how to:

  • Enable a user-assigned or system-assigned identity in a container group
  • Grant the identity access to an Azure key vault
  • Use the managed identity to access a key vault from a running container