S3 Terraform Backend

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Adam Gordon Bell %
Adam Gordon Bell

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The article simplifies the complexities of managing Terraform state. Earthly guarantees reproducible builds for Terraform projects in CI workflows. Learn more about Earthly.

In the previous article I ported all my AWS infrastructure to Terraform. But in doing so, I was left tracking all my Terraform state in a terraform.tfstate file. This has a number of problems.

First, it leaks details into a git repo that don’t need to be there. I’m not setting up an RDS database or anything, but if I did, terraform.tfstate would have my db credentials in it.

Second, if multiple people were making infra changes we would have a problem, because there would effectively be two versions of terraform.tfstate out there.

There are a number of ways to fix this. One is to move to Terraform Cloud, another is env0, but the simplest is to just to put my terraform.tfstate into an S3 bucket. And that is what I’m going to do.

Creating the Bucket

First, I’ll create a terraform bucket:

## S3 state bucket
resource "aws_s3_bucket" "tfstate" {
  bucket        = "cloudservices-terraform-state"
resource "aws_s3_bucket_acl" "tfstate" {
  bucket = aws_s3_bucket.tfstate.id
  acl    = "private"

Then I’ll apply it:

Initializing the backend...

│ Error: Error loading state:
│     AuthorizationHeaderMalformed: The authorization header is malformed; the region 'us-east-1' is wrong; expecting 'eu-west-1'
│       status code: 400, request id: ZB4DTZVN1X27HVR2, host id: 5eZcTebhqUzdTjqRmONR5MWp6orwhKcxJrmdY8+9Y5w/lVZuni3uwmLgWUDtLgci/Tsj02DFAek=

│ Terraform failed to load the default state from the "s3" backend.
│ State migration cannot occur unless the state can be loaded. Backend
│ modification and state migration has been aborted. The state in both the
│ source and the destination remain unmodified. Please resolve the
│ above error and try again.

Oh no! This confusing error means I have a name collision with someone else’s S3 bucket in us-east-1. A rename fixes things:

 resource "aws_s3_bucket" "tfstate" {
-  bucket        = "cloudservices-terraform-state"
+  bucket        = "blog-cloudservices-terraform-state"

And with that I can apply:

Plan: 2 to add, 0 to change, 0 to destroy.

Do you want to perform these actions?
  Terraform will perform the actions described above.
  Only 'yes' will be accepted to approve.

  Enter a value: yes

aws_s3_bucket.tfstate: Creating...
aws_s3_bucket.tfstate: Creation complete after 1s [id=blog-cloudservices-terraform-state]
aws_s3_bucket_acl.tfstate: Creating...
aws_s3_bucket_acl.tfstate: Creation complete after 0s [id=blog-cloudservices-terraform-state,private]

Apply complete! Resources: 2 added, 0 changed, 0 destroyed.

Next I need to add the S3 backend to my terraform section:

 terraform {
   required_providers {
     aws = {
       source = "hashicorp/aws"
+  backend "s3" {
+    bucket = "blog-cloudservices-terraform-state"
+    key    = "lambda-api"
+    region = "us-east-1"
+  }

Then Terraform walks me through the rest of the process:

$ terraform plan

Error: Backend initialization required: please run "terraform init"

Reason: Backend configuration block has changed

The "backend" is the interface that Terraform uses to store state,
perform operations, etc. If this message is showing up, it means that the
Terraform configuration you're using is using a custom configuration for
│ the Terraform backend.

│ Changes to backend configurations require reinitialization. This allows
│ Terraform to set up the new configuration, copy existing state, etc. Please run
│ "terraform init" with either the "-reconfigure" or "-migrate-state" flags to
│ use the current configuration.

│ If the change reason above is incorrect, please verify your configuration
│ hasn't changed and try again. At this point, no changes to your existing
configuration or state have been made.

Following the lead of the error message, I run terraform init -migrate-state:

$ terraform init -migrate-state

Initializing the backend...
Do you want to copy existing state to the new backend?
  Pre-existing state was found while migrating the previous "local" backend to the
  newly configured "s3" backend. No existing state was found in the newly
  configured "s3" backend. Do you want to copy this state to the new "s3"
  backend? Enter "yes" to copy and "no" to start with an empty state.

  Enter a value: yes

Successfully configured the backend "s3"! Terraform will automatically
use this backend unless the backend configuration changes.

Initializing provider plugins...
- Reusing previous version of hashicorp/aws from the dependency lock file
- Using previously-installed hashicorp/aws v4.18.0

Terraform has been successfully initialized!

You may now begin working with Terraform. Try running "terraform plan" to see
any changes that are required for your infrastructure. All Terraform commands
should now work.

If you ever set or change modules or backend configuration for Terraform,
rerun this command to reinitialize your working directory. If you forget, other
commands will detect it and remind you to do so if necessary.

And with that, all my state is now stored in S3. I can delete terraform.tfstate and terraform.tfstate.backup and I’m done.

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Adam Gordon Bell %
Spreading the word about Earthly. Host of CoRecursive podcast. Physical Embodiment of Cunningham's Law.
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