Setting up team permissions with custom RBAC role and ARM policy

Posted: 29th October 2016 by Anders Bengtsson in Azure

A common Azure infrastructure scenario is that subscription administrator setup one resource group per service/application. Service administrators or application administrators then are assigned permissions to the resource group and all resources within it. For a long time, it has been a challenge to limit what the service administrators could do within the resource group. For example, if you assigned them the permission to create a virtual machine they could create any size of virtual machine and name it anything they like. Another challenges have been two wide default security roles or two narrowed, for example if you assign service administrators the contributor role they could create any kind of resources within the resource group, but the virtual machine contributor role will not give permissions to work with public IP addresses for their services.

In this blogpost we will look into how ARM Policies and custom RBAC (Role Based Access Control) can be used to control what type of resources and how they are created within the resource group. In my example I have a resource group named CONTOSO-WE-AZFAE-RG. The naming convention is based on [ORGANIZATION]-[LOCATION West Europe in this example]-[service/workload in this example Azure Financial Analysis Engine]-[Azure Resource type in this example resource group].

The first thing is to assign permissions to the service administrators. In this scenario I want the service administrators team to have permissions to administrate everything around their virtual machines, including storage accounts, public IP addresses but not networking. The service administrators should also have permissions to connect (join) virtual machines to an existing virtual network hosted in another resource group. Azure Role-Based Access Control (RBAC) comes with a large number of security roles. Looking at the requirements in my scenario and the default roles, Virtual Machine contributor and Storage Account contributor are the two best options. I added the user account (could add a group too) as a virtual machine contributor and storage account contributor on the resource group level.

users

Now if ludvig@contoso.se, one of the service administrators, is trying to create a new virtual machine, including a new public IP and a Network Security Group, the deployment fails. This is due to the fact that the he only has permissions to virtual machines and storage accounts in the CONTOSO-WE-AZFAE-RG resource group. The Virtual Machine Contributor role have access to join machines to a subnet (Microsoft.Network/virtualNetworks/subnets/join/action) but the challenge in this scenario the VNET is hosted in another resource group. The Virtual Machine Contributor role is only for resources in the current resource group. Another challenge is that neither the Storage Account Contributor or the Virtual Machine contributor roles gives the user any permissions for public IP addresses or network security groups.

errordetails

To give the service administrators team permissions to create and administrator both public IP addresses and Network Security Groups we will create a new custom security role, as none of the built-in security roles meet the scenario requirements. We will also create a new custom security role to give the service administrator permissions to join virtual machines to the VNET. Just like built-in roles, custom roles can be assigned to users or groups and applications at subscription, resource group or resource scopes. Building custom security roles are described here. In this scenario we will build two custom security roles, the first to handle NSG and public IP permissions and second custom security role to handle join virtual machines to VNET.

This is the definition of the first role.

firstrole

This is the definition of the second role.

secondrole

To import these roles into Azure, save the definitions as for example TXT files, then run use the New-AzureRMRoleDefination Azure PowerShell cmdlet to import the file. For example, New-AzureRmRoleDefinition -InputFile ‘C:\Azure\CustomRoleOne.txt’

Once both roles are imported, assign the user these roles. The “Contoso – Read and Join VNET” role must be assigned to the users on the resource group that contains the VNET that virtual machines will be connected to.

rolesimplemented

 

A service administrator can now deploy a new virtual machine, including network security group and public IP address, in the CONTOSO-WE-AZFAE-RG resource group. A virtual machine can also be attached/connected to a VNET in another resource group, handled with the new “Contoso – Read and Join VNET” security role.

deploymentok

All good so far J

But the challenge now is that service administrators can create a virtual machine of any size and can also give the server any name. All servers should start with “AZFAE-SRV” and use a VM size from the D-family. To solve this, we will use ARM policies. With policies we can focus on resources actions, for example restrict locations or settings on a resource. If you think about this scenario we use RBAC to control what actions a user can do on virtual machines, network security groups, public IP addresses and storage accounts. We can add policies to control how these resources are provisioned, controlling the settings, for example to make sure virtual machines are always deployed in west Europe. More information about policies here.

The following script setup a new policy that restrict virtual machine name. The last three lines of the script assign the new policy to the CONTOSO-WE-AZFAE-RG resource group.

policy01

The following script setup a new policy that restrict virtual machine size. The last three lines of the script assign the new policy to the CONTOSO-WE-AZFAE-RG resource group.

policy02

If one of the Service Administrators now try to create a virtual machine with a size not D1, D2, D3 or D4 an error will occur during deployment, saying that the deployment action is disallowed by one or more policies.

errordetails2

Summary: We have now a mix of standard RBAC roles and custom RBAC roles to setup the permissions our service administrators needed. We then use ARM policies to control HOW resources are configured and deployed. The next challenge would be control how much resources the service administrator deploys. RBAC gives us control of WHAT the administrator do, ARM policies gives us control of HOW they do it. But there is no mechanism to control how many resources. For example, the service administrator in this blog post example can now deploy hundreds of D servers, if they have correct name and size.  This could be solved with an external self-service portal including approval steps , but that is out of scope for this blog post J

If you want to review policy related events, you can use the Get-AzureRMLog cmdlet and look for Microsoft.Authorization/policies events, see here for more examples.

If you want to keep track of all access changes you can use the Get-AzureRMAuthorizationChangeLog cmdlet to access the change history log. For example “Get-AzureRMAuthorizationChangeLog -StartTime ([DateTime]::Now – [TimeSpan]::FromDays(7)) | FT Caller,Action,RoleName,PrincipalType,PrincipalName,ScopeType,ScopeName” will give you a list of all access changes last week. More information about this log here.

psresult

Disclaimer: Cloud is very fast moving target. It means that by the time you’re reading this post everything described here could have been changed completely .