Implement Azure Bastion Host through Terraform

0 CommentsDecember 26, 2024

Let’s implement ‘Azure Bastion’ through Terraform as part of our Terraform hands-on scenarios/series

Do you already know what is ‘Azure Bastion’ ? if not, please refer here for details

Let’s first look at our Architecture diagram shown below to understand what all is needed for the successful implementation

In order to achieve the above, we need to first break down in to small steps— Let’s do that now as shown below

Build the basic Terraform Folder Structure

Create a folder named Az_Bastion_Laband ensure to follow and implement ‘Pre-requisites’ , 2nd and 3rd sections of my previous blog before proceeding to the next steps
Configure the backend.tf accordingly in that folder which is used to store the Terraform State remotely in the respective Azure Storage Account/Container

Create provider.tf in the same folder and have the below code which helps to configure infrastructure in Microsoft Azure platform. If you are wondering what are those under key_vault section, feel free to refer my previous blog which covers the explanation

Create variables.auto.tfvars having the default declared values like below. We defined address spaces for VNet, Subnet and also for AzureFirewallSubnet as per the needs shown in the architecture above. firewall_allocation_method and firewall_sku will be consumed for building virtual_networks in the later section and definedscale_units as 2 for AzureBastionHost for later use as well

Create variables.tf like below

Create a Resource Group

Files rg_main.tf, rg_variables.tf, rg_outputs.tf look like below. We’ve already covered the explanation of how to create Resource Groups using Terraform in our previous blogs. Hence, avoiding the duplication of explanation here but showing the code necessary for implementing this scenario [Similarly, I’ll not repeat explaining the VNets, KV and all other modules which we’ve covered in our previous blog/s. Feel free to refer them if required here and here as appropriate]

2. Create a VNet and a Subnet in that Resource Group

Apart from the VNet and Subnet, we are creating a Network Interface for our LinuxVM so that Private IP can be assigned to it

Now, our main.tf looks like below

Now perform terraform init, terraform plan and terraform apply –auto-approve one after the other successful command execution. Feel free to make use ofterraform validate and terraform fmt commands in between
You should be able to see the VNet, and Subnet in the respective RG in the portal

3. Create Azure Bastion Host and necessary components required

For a successful, Bastion Host deployment, we should create a subnet with name AzureBastionSubnet and assign a public ip to it as well. Let’s do it now
Create a folder az_bastion under modules and have the azb_main.tf, azb_variables.tf and azb_outputs.tf files as shown below

You can notice that with azb_main.tf, we are creating the AzureBastionSubnet subnet, azure publicIp and Azure Bastion Host which uses the subnet and the public-ip we created. You may notice some warning/error messages in your code as some variables like location, rg-test-name are not yet declared under az_bastion module. We’ll fix those issues in our next step with azb_variables.tf

We need resources such as public-Ip and AzureFirewallSubnet-id for our other module consumption hence they are mentioned in azb_outpputs.tf as below

Now, time to call this az_bastionmodule from main.tf

Now perform terraform init, terraform plan and terraform apply –auto-approve one after the other successful command execution.
You should be able to see the intended resources in the Azure Portal successfully

4. Use Azure Key Vault and create Secret for the LinuxVM

Let’s call the az_key_vault module from the main.tf

Now perform terraform init, terraform plan and terraform apply –auto-approve one after the other successful command execution.
You should be able to see the intended resources including the KV in the Azure Portal successfully

5. Create the LinuxVM

We’ll create the LinuxVM and assign the NIC we created before during virtual_networks module to this VM

Let’s call the vm module from the main.tf

Now perform terraform init, terraform plan and terraform apply –auto-approve one after the other successful command execution.
You should be able to see the intended resources including the VM in the Azure Portal successfully

6. Define the NSG Rules for AzureBastionHost and also for LinuxVM

Before proceeding further, I strongly recommend you to read through this excellent documentation from Microsoft explaining the NSG needs for the Bastion
We should define NSG rules for both Ingress and Egress traffic from/to the Bastion and also Ingress traffic rules for the Linux VM
Recommended Ingress and Egress rules are like below for Bastion

In order to implement the above NSG rules, let’s define traffic_rules module and implement the rules accordingly

Now, associate the NSG defined to the subnet AzureBastionSubnet like below

Define NSG rule for LinuxVM and associate it to the NIC [You can also associate it with the subnet in which this VM is present like vnet1-subnet1 in case if you want to try that option. I suggest you to understand what difference it makes associating it with the NIC vs Subnet]

[When the file contains many lines, it is not feasible to show in one shot and explain at the same time, hence I’ve divided them in to multiple snippets such as rules_main.tf Snippet_*, where * represents numbering like 1,2,3 and so on…. I believe that allows you to follow the sequence of code accordingly. Same is true for files such as main.tf. You can notice that as main.tf Snippet_*]

We don’t really have anything from the traffic_rules module to output. Hence, rules_outputs.tf is blank and it just sits there idle for the terraform schema/structure purpose
Finally, your Terraform folder structure looks like below for your visibility [Please ignore images folderand .md file ]

7. Deploy and Validate the Infrastructure

Now perform terraform init, terraform plan and terraform apply –auto-approve one after the other successful command execution. I encourage you to also use terraform validate and terraform fmt commands and fix any errors by following the blog carefully
With this, the deployment of resources is complete can be observed in your Azure Portal