Partial backend configuration in Terraform - Commands & Configuration

Introduction

When using Terraform, you can set up the backend partially to share some settings while allowing others to be configured later. This helps teams reuse common backend settings but customize details like workspace or key per environment.

When multiple Terraform projects share the same backend type but differ in specific settings like workspace or key.

When you want to enforce some backend settings centrally but allow developers to override others locally.

When you want to commit partial backend configuration to version control but keep sensitive details out.

When you want to migrate backend settings gradually without breaking existing infrastructure.

When you want to reuse backend configuration blocks across multiple Terraform modules or repos.

Config File - main.tf

main.tf

terraform {
  backend "s3" {
    bucket = "example-terraform-state"
    region = "us-east-1"
  }
}

provider "aws" {
  region = "us-east-1"
}

resource "aws_s3_bucket" "example" {
  bucket = "example-bucket-terraform"
  acl    = "private"
}

This Terraform configuration sets a partial backend for S3 with the bucket and region fixed. Other backend settings like the key or workspace can be set later by the user or environment.

The provider block configures AWS region for resource creation.

The resource block creates an S3 bucket as an example resource.

Commands

Initializes Terraform, reads the partial backend configuration, and prompts for missing backend settings like the key or workspace.

Terminal

terraform init

Expected Output

Initializing the backend...



Do you want to configure a backend? (yes/no) yes



Backend configuration required. Please enter the missing settings.



key [default]: env:dev/terraform.tfstate



Successfully configured the backend "s3"!



Terraform has been successfully initialized!



You may now begin working with Terraform. Try running "terraform plan" to see any changes.

Shows the execution plan for the resources defined, verifying that the backend is configured and state is stored remotely.

Terminal

terraform plan

Expected Output

Refreshing Terraform state in-memory prior to plan...



An execution plan has been generated and is shown below.

Resource actions are indicated with the following symbols:

  + create



Terraform will perform the following actions:



  # aws_s3_bucket.example will be created

  + resource "aws_s3_bucket" "example" {

      + acl    = "private"

      + bucket = "example-bucket-terraform"

      + id     = (known after apply)

    }



Plan: 1 to add, 0 to change, 0 to destroy.

Applies the planned changes, creating the S3 bucket and storing state in the configured backend.

Terminal

terraform apply -auto-approve

Expected Output

aws_s3_bucket.example: Creating...

aws_s3_bucket.example: Creation complete after 2s [id=example-bucket-terraform]



Apply complete! Resources: 1 added, 0 changed, 0 destroyed.

→

-auto-approve - Skips interactive approval prompt to apply changes immediately

Key Concept

Partial backend configuration lets you fix some backend settings in code while supplying others interactively or per environment.

Common Mistakes

Defining all backend settings in the config file but expecting Terraform to prompt for missing ones.

Terraform will not prompt if all backend settings are present; partial config requires some settings to be omitted.

Omit the settings you want to supply later, like 'key' or 'workspace', to enable partial backend configuration.

Running 'terraform init' without supplying missing backend settings interactively or via CLI/environment.

Terraform initialization will fail or hang waiting for backend configuration input.

Provide missing backend settings when prompted or supply them via CLI flags or environment variables.

Summary

Create a Terraform config with partial backend settings, omitting some keys like 'key' or 'workspace'.

Run 'terraform init' to initialize and supply missing backend settings interactively.

Use 'terraform plan' and 'terraform apply' to manage infrastructure with the backend storing state remotely.