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Federate Coder's control plane to Azure

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January 26, 2024

This guide will walkthrough how to authenticate a Coder Provisioner to Microsoft Azure, using a Service Principal with a client certificate. You can use this guide for authenticating Coder to Azure, regardless of where Coder is run, either on-premise or in a non-Azure cloud. This method is one of several recommended by Terraform.

Step 1: Generate Client Certificate & PKCS bundle

We'll need to create the certificate Coder will use for authentication. Run the below command to generate a private key and self-signed certificate:

openssl req -subj '/CN=myclientcertificate/O=MyCompany, Inc./ST=CA/C=US' \
  -new -newkey rsa:4096 -sha256 -days 730 -nodes -x509 -keyout client.key -out client.crt

Next, generate a .pfx file to be used by Coder's Provisioner to authenticate the AzureRM provider:

openssl pkcs12 -export -password pass:"Pa55w0rd123" -out client.pfx -inkey client.key -in client.crt

Step 2: Create Azure Application & Service Principal

Navigate to the Azure portal, and into the Microsoft Entra ID section. Select the App Registration blade, and register a new application. Fill in the following fields:

Name: this is a friendly identifier and can be anything (for example, "Coder")
Supported Account Types: - set to "Accounts in this organizational directory only (single-tenant)"

The Redirect URI field does not need to be set in this case. Take note of the Application (client) ID and Directory (tenant) ID values, which will be used by Coder.

Step 3: Assign Client Certificate to the Azure Application

To upload the certificate we created in Step 1, select Certificates & secrets on the left-hand side, and select Upload Certificate. Upload the public key file, which is service-principal.crt from the example above.

Step 4: Set Permissions on the Service Principal

Now that the Application is created in Microsoft Entra ID, we need to assign permissions to the Service Principal so it can provision Azure resources for Coder users. Navigate to the Subscriptions blade in the Azure Portal, select the Subscription > Access Control (IAM) > Add > Add role assignment.

Set the Role that grants the appropriate permissions to create the Azure resources you need for your Coder workspaces. Contributor will provide Read/Write on all Subscription resources. For more information on the available roles, see the Microsoft documentation.

Step 5: Configure Coder to use the Client Certificate

Now that the client certificate is uploaded to Azure, we need to mount the certificate files into the Coder deployment. If running Coder on Kubernetes, you will need to create the .pfx file as a Kubernetes secret, and mount it into the Helm chart.

Run the below command to create the secret:

kubectl create secret generic -n coder azure-client-cert-secret --from-file=client.pfx=/path/to/your/client.pfx

In addition, create secrets for each of the following values from your Azure Application:

Client ID
Tenant ID
Subscription ID
Certificate password

Next, set the following values in Coder's Helm chart:

coder:
  env:
    - name: ARM_CLIENT_ID
      valueFrom:
        secretKeyRef:
          key: id
          name: arm-client-id
    - name: ARM_CLIENT_CERTIFICATE_PATH
      value: /home/coder/az/
    - name: ARM_CLIENT_CERTIFICATE_PASSWORD
      valueFrom:
        secretKeyRef:
          key: password
          name: arm-client-cert-password
    - name: ARM_TENANT_ID
      valueFrom:
        secretKeyRef:
          key: id
          name: arm-tenant-id
    - name: ARM_SUBSCRIPTION_ID
      valueFrom:
        secretKeyRef:
          key: id
          name: arm-subscription-id
  volumes:
    - name: "azure-client-cert"
      secret:
        secretName: "azure-client-cert-secret"
  volumeMounts:
    - name: "azure-client-cert"
      mountPath: "/home/coder/az/"
      readOnly: true

Upgrade the Coder deployment using the following helm command:

helm upgrade coder coder-v2/coder -n coder -f values.yaml