Bastion (Transit) Networks Are the DMZ to Protect Your Cloud from Your Datacenter

By Rich

In an earlier post I mentioning bastion accounts or virtual networks. Amazon calls these “transit VPCs” and has a good description. Before I dive into details, the key difference is that I focus on using the concept as a security control, and Amazon for network connectivity and resiliency. That’s why I call these “bastion accounts/networks”.

Here is the concept and where it comes from:

  • As I have written before, we recommend you use multiple account with a partitioned network architecture structure, which often results in 2-4 accounts per cloud application stack (project). This limits the ‘blast radius’ of an account compromise, and enables tighter security control on production accounts.
  • The problem is that a fair number of applications deployed today still need internal connectivity. You can’t necessarily move everything up to the cloud right away, and many organizations have entirely legitimate reasons to keep some things internal. If you follow our multiple-account advice, this can greatly complicate networking and direct connections to your cloud provider.
  • Additionally, if you use a direct connection with a monolithic account & network at your cloud provider, that reduces security on the cloud side. Your data center is probably the weak link – unless you are as good at security as Amazon/Google/Microsoft. But if someone compromises anything on your corporate network, they can use it to attack cloud assets.
  • One answer is to create a bastion account/network. This is a dedicated cloud account, with a dedicated virtual network, fo the direct connection back to your data center. You then peer the bastion network as needed with any other accounts at your cloud provider. This structure enables you to still use multiple accounts per project, with a smaller number of direct connections back to the data center.
    • It even supports multiple bastion accounts, which only link to portions of your data center, so they only gain access to the necessary internal assets, thus providing better segregation. Your ability to do this depends a bit on your physical network infrastructure, though.
    • You might ask how this is more secure. It provides more granular access to other accounts and networks, and enables you to restrict access back to the data center. When you configure routing you can ensure that virtual networks in one account cannot access another account. If you just use a direct connect into a monolithic account, it becomes much harder to manage and maintain those restrictions.
    • It also supports more granular restrictions from your data center to your cloud accounts (some of which can be enforced at a routing level – not just firewalls), and because you don’t need everything to phone home, accounts which don’t need direct access back to the data center are never exposed.

A bastion account is like a weird-ass DMZ to better control access between your data center and cloud accounts; it enables multiple account architectures which would otherwise be impossible. You can even deploy virtual routing hardware, as per the AWS post, for more advanced configurations.

It’s far too late on a Friday for me to throw a diagram together, but if you really want one or I didn’t explain clearly enough, let me know via Twitter or a comment and I’ll write it up next week.

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