Azure Virtual WAN Route Maps and Reflected Routes

Microsoft have make controlling routing within a Virtual WAN much easier thanks to a combination of Routing Intent and Route Maps (in preview at time of writing). Route Maps work in the same manner (at least theoretically) to route map configuratons network administrators are used to in on-premises equipment.

In testing tehm out for a customer, I ran straight into a problem. I like to keep things tidy, and when I looked at the output of the outbound route map configuration for a site to site VPN with AWS, I didn’t like that it showed all my AWS routes being published back out to the VPN. So I configured a route map rule to drop reflected routes.

Grant Admin Consent for an Azure AD application with Terraform

One challenge we often run into when provisioning Azure AD applications with Terraform is a need to grant admin consent for API permissions. Sadly there is not a native resource within Terraform to make this happen, however with some creative use of provisioners (yes, I feel bad about it too) we can ensure that admin consent is granted for our applications.

To start with, we deploy our Azure AD application as normal. As part of the configuration, we also assign the required API permissions.

Authenticating Terraform with a GitHub App

In my current role, I configured Terraform to manage our GitHub organisation. As with all providers, we need need to provide credentials for authentication. I didn’t want to use an access token, as they are tied to an individual user and will cause breakage should the user depart the organisation. Thankfully, GitHub supports using an application for authentication.

Create the GitHub Application

The first step in the process is to create a new GitHub application. While this can be done either in a personal account or within an organisation, I recommend doing this within the organisation. That way, if someone leaves the organisation the application doesn’t go with.

App Service, App Settings, and Container Registry with Managed Identity

Managed Identities in Azure are a wonderful thing. No passwords to change, no keys to rotate. The biggest shame is that frequently they seem to be implemented as an afterthought.

One example I recently ran into was the use of an App Service Managed Identity to pull a container from Azure Container Registry. While you can configure an App Service to pull from ACR with a Managed Identity, what the documentation doesn’t tell you is that you still need the DOCKER_REGISTRY_SERVER_USERNAME and DOCKER_REGISTRY_SERVER_PASSWORD App Settings to be configured on the App Service. It doesn’t matter what values you put in these, the point is they must exist. If they don’t, the container will fail to pull with a credential error.

Using Table Storage as an Alternative to Remote State

Terraform is a fantastic tool for Infrastructure as Code. From the YAML-like HCL syntax (no JSON!), to importing files (linting JSON files FTW!), to retrieving the results of previous runs to link resources, Terraform has made a massive difference in my work. However, like all technologies, it is not without its weaknesses. Terraform uses state files to keep track of what the world looked like when it last ran, which is wonderful for identifying drift. The default pattern is to use these state files for passing data between Terraform modules. But this is actually an anti-pattern, for HashiCorp recommend not using remote state for passing data, in large part because to read the outputs from a state file the caller must have full access to read the entire remote state file, which include secrets they probably shouldn’t be allowed to access.

Deploying Terraform via a DevOps Pipeline

Not everyone is privileged to be able to use Terraform Cloud for deploying their Terraform infrastructure. This means that teams need to use their existing DevOps tooling to deploy their infrastructure via Terraform.

While I’ve seen many examples of pipelines for deploying Terraform code with various services, it felt like something was missing. Most example pipelines were designed to just run once a code review had occurred, and often would automatically deploy the changed code without any intervention. This wasn’t going to fly for us in a recent project. We needed a more robust plan for deployment, one that would cater for not only deployment of the infrastructure, but an opportunity to wait for approval of a specific plan, plus checks to make sure that the newly-committed code was up to standard.

Allow Traffic Manager Probes Through Azure Firewall

Traffic Manager is an essential component of any resilient deployment within Azure. Whether you have a multi-region behemoth, or simply want a simple way to activate DR instances should the primary go down, Traffic Manager has a configuration for you. One key component of Traffic Manager is its probes—by frequently checking the status of your application, Traffic Manager can make intelligent decisions about where to direct the traffic.

As with all services, there are a specific set of IP addresses from which the probes will originate. Microsoft even helpfully provide a Service Tag AzureTrafficManager which is kept up-to-date with the latest IP addresses used by Traffic Manager probes. They even tell us that this Service Tag is supported for use in Azure Firewall.¹ Except… that is not the whole story.