Access policies vs RBAC in Azure - Performance Comparison

Time Complexity: Access policies vs RBAC

O(n)

Understanding Time Complexity

We want to understand how the time to check permissions grows when using access policies versus role-based access control (RBAC) in Azure.

How does the system handle more users or resources when deciding access?

Scenario Under Consideration

Analyze the time complexity of permission checks using access policies and RBAC.

// Access policy check
var isAllowed = CheckAccessPolicy(user, resource);

// RBAC check
var roles = GetUserRoles(user);
var isAllowed = CheckRolePermissions(roles, resource);

This sequence checks if a user can access a resource either by direct access policies or by roles assigned to the user.

Identify Repeating Operations

Look at what repeats when checking access for many users or resources.

• Primary operation: Checking user permissions via policies or roles.
• How many times: Once per access request, repeated for each user-resource pair.

How Execution Grows With Input

As the number of users or resources grows, the checks increase accordingly.

Input Size (n)	Approx. API Calls/Operations
10	10 permission checks
100	100 permission checks
1000	1000 permission checks

Pattern observation: The number of permission checks grows directly with the number of access requests.

Final Time Complexity

Time Complexity: O(n)

This means the time to check permissions grows linearly with the number of access requests.

Common Mistake

[X] Wrong: "Checking access policies or RBAC is instant and does not depend on the number of users or resources."

[OK] Correct: Each access check requires looking up policies or roles, so more users or resources mean more checks and more time.

Interview Connect

Understanding how permission checks scale helps you design systems that stay fast as they grow, a key skill in cloud architecture.

Self-Check

"What if we cached user roles after the first check? How would that affect the time complexity of RBAC permission checks?"

Practice

1. What is the main difference between Azure Access Policies and RBAC?

easy

A. RBAC controls network traffic; Access Policies manage user passwords.

B. Access Policies grant permissions directly on resources; RBAC assigns roles at scopes.

C. Access Policies are used only for virtual machines; RBAC is for databases.

D. RBAC is a legacy system; Access Policies are the modern replacement.

Solution

1. Step 1: Understand Access Policies

   Access Policies give permissions directly on specific resources, like a key vault.

2. Step 2: Understand RBAC

   RBAC assigns roles with permissions at different levels like subscription or resource group.

3. Final Answer:

   Access Policies grant permissions directly on resources; RBAC assigns roles at scopes. -> Option B

4. Quick Check:

   Access Policies = direct resource permissions, RBAC = role-based scopes [OK]

Hint: Access Policies = direct, RBAC = role at scope [OK]

Common Mistakes:

• Confusing Access Policies with RBAC roles
• Thinking RBAC only applies to virtual machines
• Assuming Access Policies control network settings

2. Which of the following is the correct way to assign an RBAC role using Azure CLI?

easy

A. az network policy add --role <role> --user <user>

B. az accesspolicy set --user <user> --permission <perm>

C. az vm assign-role --user <user> --role <role>

D. az role assignment create --assignee <user> --role <role> --scope <scope>

Solution

1. Step 1: Identify correct RBAC command

   The Azure CLI command to assign RBAC roles is 'az role assignment create' with assignee, role, and scope parameters.

2. Step 2: Verify other options

   Other options mention access policies or unrelated commands which are invalid for RBAC role assignment.

3. Final Answer:

   az role assignment create --assignee <user> --role <role> --scope <scope> -> Option D

4. Quick Check:

   RBAC role assignment uses 'az role assignment create' [OK]

Hint: RBAC role assignment uses 'az role assignment create' [OK]

Common Mistakes:

• Using access policy commands for RBAC
• Mixing VM or network commands with RBAC
• Omitting the scope parameter

3. Given this Azure CLI command output snippet for a key vault access policy:

"permissions": {"keys": ["get", "list"], "secrets": ["get"]}

What permissions does this policy grant?

medium

A. Allows only listing keys, no secret access.

B. Allows creating and deleting keys and secrets.

C. Allows getting and listing keys, and getting secrets.

D. Allows full control over keys and secrets.

Solution

1. Step 1: Read the permissions for keys

   The keys permission includes 'get' and 'list', so it allows reading and listing keys.

2. Step 2: Read the permissions for secrets

   The secrets permission includes only 'get', so it allows reading secrets but no other actions.

3. Final Answer:

   Allows getting and listing keys, and getting secrets. -> Option C

4. Quick Check:

   Permissions match get/list keys and get secrets [OK]

Hint: Check each permission list carefully for allowed actions [OK]

Common Mistakes:

• Assuming 'get' means create or delete
• Confusing 'list' with full control
• Ignoring secret permissions

4. You assigned an RBAC role to a user but they still cannot access a key vault secret. What is the most likely cause?

medium

A. The user lacks an access policy granting secret permissions on the key vault.

B. The RBAC role was assigned at subscription level, which is too broad.

C. The user needs to restart their Azure portal session.

D. RBAC roles do not control access to key vault secrets.

Solution

1. Step 1: Understand RBAC vs Access Policies for Key Vault

   Key vault secrets require access policies to grant permissions, RBAC alone may not suffice.

2. Step 2: Analyze the problem

   Even if RBAC role is assigned, without an access policy granting secret permissions, access is denied.

3. Final Answer:

   The user lacks an access policy granting secret permissions on the key vault. -> Option A

4. Quick Check:

   Key vault secret access requires access policies [OK]

Hint: Key vault secrets need access policies, not just RBAC [OK]

Common Mistakes:

• Assuming RBAC alone controls key vault secrets
• Thinking subscription-level RBAC restricts access
• Believing portal restart fixes permission issues

5. You want to secure an Azure Key Vault so that only a specific user can read secrets, and a group can manage keys. Which approach follows best practices?

hard

A. Assign specific RBAC roles to the user for secret read (Key Vault Secrets User) and to the group for key management (Key Vault Crypto Officer).

B. Create an access policy granting the user secret read permission; assign an RBAC role to the group for key management.

C. Use access policies for both user and group to grant all permissions.

D. Assign the user an RBAC role for secrets and the group an access policy for keys.

Solution

1. Step 1: Choose RBAC as best practice

   Azure recommends RBAC for Key Vault. Disable access policies and enable RBAC authorization on the Key Vault.

2. Step 2: Assign granular roles at Key Vault scope

   Assign 'Key Vault Secrets User' role to user (get/list secrets). Assign 'Key Vault Crypto Officer' role to group (manage keys).

3. Final Answer:

   Assign specific RBAC roles to the user for secret read (Key Vault Secrets User) and to the group for key management (Key Vault Crypto Officer). -> Option A

4. Quick Check:

   RBAC Secrets User + Crypto Officer roles [OK]

Hint: RBAC best practice: Secrets User + Crypto Officer roles [OK]

Common Mistakes:

• Trying to mix Access Policies and RBAC (not possible)
• Using access policies for everything (legacy method)
• Assigning overly broad roles or permissions