100 Days of Cloud – Day 42: Azure Bastion

Its Day 42 of my 100 Days of Cloud Journey, and today I’m taking a look at Azure Bastion.

Azure Bastion is a PaaS VM that you provision inside your virtual network, providing secure and seamless RDP or SSH connectivity to your IAAS VMs directly from the Azure portal over TLS. When you connect via Azure Bastion, your virtual machines do not need a public IP address, agent, or special client software.

We saw in previous posts that when we create a VM in Azure, it automatically creates a Public IP Address, access to which we then need to control using Network Security Groups. Azure Bastion does away with the need for controlling access – all you need to do is create rules to allow RDP/SSH access from the subnet where Bastion is deployed to the subnet where your IAAS VMs are deployed.

Deployment

Image Credit – Microsoft
  • We can see in the diagram a typical Azure Bastion deployment. In this diagram:
    • The bastion host is deployed in the VNet.
      • Note – The protected VMs and the bastion host are connected to the same VNet, although in different subnets.
    • A user connects to the Azure portal using any HTML5 browser over TLS.
    • The user selects the VM to connect to.
    • The RDP/SSH session opens in the browser.
  • To deploy an Azure Bastion host by using the Azure portal, start by creating a subnet in the appropriate VNet. This subnet must:
    • Be named AzureBastionSubnet
    • Have a prefix of at least /27
    • Be in the VNet you intend to protect with Azure Bastion

Cross-VNET Connectivity

Bastion can also take advantage of VNET Peering rules in order to connect to VMs in Multiple VNETs that are peered with the VNET where the Bastion host is located. This negates the need for having multiple Bastion hosts deployed in all of your VNETs. This works best in a “Hub and Spoke” configuration, where the Bastion is the Hub and the peered VNETs are the spokes. The diagram below shows how this would work:

Design and Architecture diagram
Image Credit – Microsoft
  • To connect to a VM through Azure Bastion, you’ll require:
    • Reader role on the VM.
    • Reader role on the network information center (NIC) with the private IP of the VM.
    • Reader role on the Azure Bastion resource.
    • The VM to support an inbound connection over TCP port 3389 (RDP).
    • Reader role on the virtual network (for peered virtual networks).

Security

One of the key benefits of Azure Bastion is that its a PAAS Service – this means it is managed and hardened by the Azure Platform and protects againsts zero-day exploits. Because your IAAS VMs are not exposed to the Internet via a Public IP Address, your VMs are protected against port scanning by rogue and malicious users located outside your virtual network.

Conclusion

We can see how useful Bastion can be in protecting our IAAS Resources. You can run through a deployment of Azure Bastion using the “How-to” guides on Microsoft Docs, which you will find here.

Hope you enjoyed this post, until next time!

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