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Azure Front Door IP Group Updater

Simple application that updates IP Groups in Microsoft Azure with the IP Ranges currently configured for Azure Front Door. While Network Security Groups have the required service tags to limit acccess to Azure Front Door, Azure Firewall does not. This aims to mitigate that.

Usage

Create a Service Principal

The Application requires a Service Principal with Contributor access to the IP Group you intend to use. The below assumes you've already created the relevant resource.

Firstly, create a Service Principal with the following:

$ az ad sp create-for-rbac -n "Azure Front Door IP Group Updater"

This should return a payload similar to the below, make a note of it for later:

{
  "appId": "8fcd040b-6966-452e-b006-83670131e941",
  "displayName": "Azure Front Door IP Group Updater",
  "password": "some_super_secret_secret",
  "tenant": "e457378e-e0b3-4edc-95a8-20de1ea662f1"
}

Note: by default the secret created for this user will expire in 12 months, make sure to setup a way to detect this and handle it appropriately.

Assign the Application to the IP Group

Get the Principal ID of the new Service Principal you just created:

$ az ad sp show --id "{appId}" | jq -r .id

Now use that to assign the Service Principal to the AzureRM Resource.

$ az role assignment create \
  --assignee "{princial_ip}" \
  --role "Contributor" \
  --scope "/subscriptions/{your_subscription}/resourceGroups/{your_resource_group}/providers/Microsoft.Network/ipGroups/{ip_group_name}"

Create and Assign a Custom Role for viewing Service Tags

Create a file called role.json with the following content

{
    "Name": "Service Tag Reader",
    "IsCustom": true,
    "Description": "Reads Service Tags via Rest API",
    "Actions": [
        "Microsoft.Network/locations/serviceTagDetails/read"
    ],
    "NotActions": [],
    "AssignableScopes": [
        "/subscriptions/{your_subscription}",
    ]
}

Now apply this with:

$ az role definition create --role-definition role.json

Finally, assign the role with:

$ az role assignment create \
  --assignee "{princial_ip}" \
  --role "Service Tag Reader" \
  --scope "/subscriptions/{your_subscription}"

Run the Application

The Application can be run in one of four ways:

  1. Locally in Python 3.10, use a .env or config.toml file, or manually do a bunch of export commands if you're into that.
  2. Locally via Docker
  3. Azure Kubernetes Service using Environment Variables
  4. Azure Kubernetes Service using config.toml

Below is an example of running this with Environment Variables using Docker:

$ docker run --rm --name frontdoor-iprange-updater \
    -e application_id="8fcd040b-6966-452e-b006-83670131e941" \
    -e application_secret="some_super_secret_secret" \
    -e tenant_id="e457378e-e0b3-4edc-95a8-20de1ea662f1" \
    -e subscription_id="3fbfae19-cdb6-49b7-b2cb-b297d067fa92" \
    -e resource_group_name="uksouth-firewall" \
    -e ip_group_name="frontdoor_ips" \
    ghcr.io/cpressland/frontdoor-ipgroup-updater:latest

For an AKS install, I'd recommend you use Flux v2 and use a configMapGenerator to inject a config.toml file into /app, and inject the application_secret into a file called /var/run/secrets/frontdoor-ipgroup-updater/application_secret, using a secretGenerator or whatever mechanism you prefer. config.toml example:

application_id = "8fcd040b-6966-452e-b006-83670131e941"
tenant_id = "e457378e-e0b3-4edc-95a8-20de1ea662f1"
subscription_id = "3fbfae19-cdb6-49b7-b2cb-b297d067fa92"
resource_group_name = "uksouth-firewall"
ip_group_name = "frontdoor_ips"

Note, application_secret is missing from the config file as its expected that you'd inject it via the aformentioned file in /var/run/secrets. Pydantic allows any configuration to be stored as a file, config, or environment variable. So you can mix and match for whatever works for you.