Collaborate easier with Terraform remote backend

Collaborating on infrastructure as code (IaC) projects with Terraform can be both empowering and challenging, especially when multiple team members need to work simultaneously on the same resources. The potential for conflicting changes and unintended disruptions looms large without a structured approach. Enter Terraform’s remote backend solutions, offering a lifeline in the storm of collaborative development. By leveraging remote backends, teams can centralize their state management, maintain version control integrity, and ensure seamless collaboration across distributed teams. This blog explores the nuances of using Terraform in a team setting, the pitfalls of concurrent resource modification, and the transformative benefits of adopting remote backends to streamline development workflows and enhance project scalability and stability.

How a Remote Backend Enhances Collaboration in Terraform

Using a remote backend for Terraform state management offers several key benefits that enhance collaboration among developers:

Centralized State Management:

A remote backend allows the Terraform state file to be stored in a central location accessible to all team members. This ensures that everyone is working with the same state information, avoiding discrepancies and conflicts that can arise from using local state files.

State Locking:

Remote backends like AWS S3 paired with DynamoDB provide state locking, which prevents multiple developers from making concurrent changes to the state file. This mechanism ensures that only one operation modifies the state at a time, maintaining consistency and preventing race conditions.

Versioning and History:

Using remote storage solutions like S3 enables versioning of the state file. This allows teams to track changes, revert to previous states if needed, and audit state changes over time.

Access Control:

Centralized storage allows you to apply strict access control policies using AWS IAM, ensuring that only authorized users can modify or view the state file.

How It Works

Setting Up AWS S3 and DynamoDB for Terraform State

Create an S3 Bucket:

The S3 bucket will store the Terraform state file. Enabling versioning on the bucket allows you to maintain a history of state file changes. This can be a S3 bucket in each account.

Create a DynamoDB Table for State Locking:

The DynamoDB table will handle state locks, preventing multiple operations from occurring simultaneously. This can either be shared between accounts or one per account. (I do not have any preference except that it would cost more if we go with a DynamoDB per account)

Configure Terraform to Use the Remote Backend:

Update your Terraform configuration to point to the remote backend using the S3 bucket and DynamoDB table. This setup ensures that the state is stored remotely and locked during operations. eg.

terraform {
  backend "s3" {
    bucket         = "your-terraform-state-bucket"
    key            = "path/to/your/terraform.tfstate"
    region         = "your-region"
    dynamodb_table = "terraform-locks"
  }
}

Workflow with Remote Backend

1. Initialization:

When a developer initializes Terraform (terraform init), it configures the backend and sets up the necessary connection to the S3 bucket and DynamoDB table.

2. State Retrieval and Locking:

When running a Terraform command like terraform plan or terraform apply, Terraform retrieves the state file from the S3 bucket. If the operation modifies the state, Terraform first acquires a lock from the DynamoDB table. This lock prevents other Terraform operations from running simultaneously.

3. State Updates:

After acquiring the lock, Terraform performs the necessary operations and updates the state file in the S3 bucket. The state file is then versioned, providing a history of changes.

4. Releasing the Lock:

Once the operation is complete, Terraform releases the lock in the DynamoDB table, allowing other operations to proceed.

Terraform Remote Backend Workflow Visualization

The diagram above illustrates the workflow of using a remote backend for Terraform state management, enhancing collaboration among developers.

1. Initialization:

• Developer A and Developer B run terraform init, which configures the Terraform backend and connects to the S3 bucket and DynamoDB table.

2. State Retrieval:

• When a developer runs terraform plan or terraform apply, Terraform retrieves the current state from the S3 bucket.

3. State Locking:

• Terraform acquires a lock from the DynamoDB table to prevent other operations from modifying the state concurrently.

4. Apply Changes:

• The developer applies changes to the infrastructure. Terraform updates the state file in the S3 bucket with the new configuration.

5. State Update:

• The updated state file is versioned and stored in the S3 bucket.

6. Release Lock:

• After the changes are applied and the state is updated, Terraform releases the lock in the DynamoDB table, allowing other operations to proceed.

Handling Concurrent Operations in Terraform

When two developers try to run terraform init or terraform apply at the same time, Terraform’s backend configuration ensures that operations are handled safely and consistently. Here’s how this is managed:

1. terraform init

No Conflict: The terraform init command is safe to run concurrently because it primarily involves setting up the backend configuration and downloading provider plugins. It doesn’t modify the state file, so no state locking is needed.

2. terraform plan

No State Locking: Unlike terraform apply, terraform plan does not modify the state file. Therefore, it does not require state locking. Safe to Run Concurrently: Multiple developers can run terraform plan at the same time without any conflict, as this command only reads the state and configuration files to generate the plan.

3. terraform apply

State Locking Mechanism: When multiple developers attempt to run terraform apply simultaneously, the backend configuration (specifically using AWS S3 and DynamoDB) will manage this using state locking.

• Lock Acquisition: Terraform tries to acquire a lock from the DynamoDB table before making any changes to the state.
• Lock Contention: If one developer has already acquired the lock, other attempts will be blocked until the lock is released.
• Retry Mechanism: The blocked operations will retry acquiring the lock after a short delay, ensuring that changes are applied sequentially.

Workflow with Concurrent terraform apply Commands

• Developer A runs terraform apply.

• Terraform connects to the S3 bucket to retrieve the state file.

• Terraform acquires a lock from the DynamoDB table.

• Developer A’s changes are applied to the infrastructure.

• Terraform updates the state file in the S3 bucket and releases the lock.

• Developer B runs terraform apply at the same time.

• Terraform connects to the S3 bucket to retrieve the state file.

• Terraform attempts to acquire a lock from the DynamoDB table.

• If Developer A already holds the lock, Developer B’s operation is blocked.

• Once Developer A’s operation completes and the lock is released, Developer B’s operation proceeds.

• Developer B’s changes are then applied, and the state file is updated.

Visual Workflow of Concurrent terraform apply

Developer A: terraform apply
|
|--- State file retrieved from S3
|--- Lock acquired from DynamoDB
|--- Changes applied to infrastructure
|--- State file updated in S3
|--- Lock released in DynamoDB
|                    |
Developer B: terraform apply (simultaneously)
|
|--- State file retrieved from S3
|--- Attempt to acquire lock from DynamoDB
|                    |--- Lock not available (blocked)
|                    |--- Lock acquired after Developer A releases it
|--- Changes applied to infrastructure
|--- State file updated in S3
|--- Lock released in DynamoDB

Ensuring Smooth Collaboration

To minimize conflicts and ensure smooth collaboration, consider the following best practices:

Communication:

Encourage team members to communicate and coordinate when making significant infrastructure changes.

Granular Work:

Break down infrastructure changes into smaller, more manageable pieces to reduce the likelihood of conflicts.

Lock Timeout:

Configure appropriate lock timeout settings in Terraform to avoid long wait times if a lock is not released due to an issue.

Conclusion

In the realm of infrastructure as code (IaC), successful collaboration hinges not only on technical prowess but also on effective communication and change management practices. Terraform’s remote backend solutions play a pivotal role in this equation, offering a structured framework for managing state and version control across teams. By centralizing state management and implementing robust change management processes, teams can mitigate the risks of conflicting modifications and ensure consistent deployment outcomes. Embracing tools like Terraform remote backend underscores the importance of fostering a collaborative environment where transparency, communication, and shared understanding pave the way for scalable, efficient, and reliable infrastructure management. As teams navigate the complexities of modern IT landscapes, these tools serve as indispensable allies in achieving agility, resilience, and innovation in cloud infrastructure deployment.