AWS multi-region Terraform.
A Terraform module set that builds the same infrastructure in 16 AWS regions from one locals map per region.
Problem
The same resources had to exist in many regions. More regions meant more copied code and a higher risk that regions drift apart.
Approach
A locals map per region declares the wanted state, and module plus for_each creates it all. Each region has a provider alias that assumes the same role. Terraform cannot choose a provider dynamically inside for_each, so the module block repeats per region.
Implementation
- Terraform
- AWS
- EKS
- CloudWatch
- AWS Chatbot
Scale · 16 regions · 24 modules · 3 examples
Each of the 16 AWS regions gets its own provider alias.
Every alias assumes the same role. The Americas connect first.
Six Asia Pacific regions join through the same role.
Five European regions join, and all 16 regions are on.
Adding a region means one more locals entry and one more module block.
Read every step
- Each of the 16 AWS regions gets its own provider alias.
- Every alias assumes the same role. The Americas connect first.
- Six Asia Pacific regions join through the same role.
- Five European regions join, and all 16 regions are on.
- Adding a region means one more locals entry and one more module block.
Result
A change is one map entry, and stable keys mean reordering never recreates anything. The 24 modules carry defaults for encryption, IMDSv2, and private S3, and three examples cover networks, EKS, and alerting.
- 16
- Regional provider aliases
- 24
- Terraform modules
- 3
- Validated examples
What I learned
Stable keys mattered as much as less repetition. count identifies resources by their position in a list, so inserting or reordering an entry can recreate everything after it, while for_each identifies them by map key, so the same resource is addressed whatever the order. Terraform cannot pick a provider inside for_each, and instead of hiding that limit, I repeated the module block per region in plain sight, which turned out easier to read and change. Since then, when the same structure has to exist in many places, I separate data (the map) from code (the module) first, and I judge the design by whether a change ends at one map entry.
16 regions — 24 modules, one locals map per region