What is state locking in Terraform?
When we’re managing infrastructure as code (IAC) with Terraform, ensuring the safety and consistency of our infrastructure is paramount. Terraform’s state management is a crucial aspect of this and state locking is one of the techniques it employs to safeguard the infrastructure deployments.
Understanding Terraform state
In Terraform, the state represents the current state of our infrastructure. It contains the following properties:
Information about the resources we’ve created
Their attributes
Their dependencies
Terraform uses this state information to plan and execute changes to our infrastructure.
The need for state locking
Imagine a scenario where multiple team members are working on the same Terraform project simultaneously. Without state locking, there’s a risk of conflicts when two or more people try to apply changes to the same infrastructure concurrently. These conflicts can lead to unintended resource modifications or errors, potentially causing downtime or data loss.
This is where state locking becomes crucial. It prevents concurrent write operations to the Terraform state, ensuring that only one person can make changes at a time, thereby avoiding conflicts.
How state locking works
State locking operates as follows:
Remote backend: Terraform stores the state file remotely, often using services like Amazon S3 or Azure Blob Storage.
Dedicated locking mechanism: Terraform employs a dedicated locking mechanism, such as a DynamoDB table or a Consul cluster, to coordinate locks. This mechanism ensures that only one person can make changes to the state at any given time.
Lock check: Before executing any operation, Terraform checks if the state file is locked.
Wait mechanism: If a lock is detected, Terraform patiently waits until the lock is released. It prevents concurrent write operations to avoid conflicts.
Exclusive access: Only one operation can modify the state at any given time, ensuring exclusive access and preventing unintended changes.
Note: Most remote backends used by Terraform support state locking. When we initiate a
terraform applycommand, the tool automatically requests a lock on the state file. If a lock is already in place—indicating that another process is making changes—Terraform will wait for the lock to be released. To customize this behavior, we can use the-lock-timeout=<TIME>parameter, allowing us to specify the maximum time Terraform should wait for the lock to be released.
The illustration below gives an overview of how this process works:
Example
Here’s an example of how state locking can be enabled using a remote back-end configuration in a Terraform configuration file:
terraform {backend "s3" {bucket = "my-terraform-state"key = "terraform.tfstate"region = "us-east-1"encrypt = truedynamodb_table = "tf-state-lock"}}
The components of the code above are listed as follows:
backend "s3": This specifies the use of Amazon S3 as the remote backend.bucket: This is the name of the S3 bucket where the state file will be stored.key: This is the name of the state file within the bucket.region: This is the AWS region where the S3 bucket is located.encrypt: This option enables encryption for the state file.dynamodb_table: This option specifies the DynamoDB table (tf-state-lock) for locking.
By configuring our Terraform projects in this manner, we can enhance security and ensure smooth collaboration while managing IAC.
Best practices for state locking
To effectively use state locking in Terraform, consider the following best practices:
Use a remote backend: Storing the Terraform state in a remote backend, such as Amazon S3 or Azure Blob Storage, is a good practice. These services provide built-in support for state locking and are highly available and durable.
Enable encryption: Always enable encryption for the state files to ensure the security of the infrastructure data.
Use a dedicated locking mechanism: Utilize a dedicated mechanism for state locking, such as a DynamoDB table or a Consul cluster. Avoid sharing locks with other systems or processes.
Implement locking strategy: Define a strategy for acquiring and releasing locks. Avoid long-running operations that could potentially block other users from making changes.
By adhering to these best practices, we can enhance the reliability and safety of our Terraform deployments when working collaboratively.
Conclusion
State locking in Terraform is a fundamental feature that helps maintain the integrity of our IAC projects, particularly in multiuser and collaborative environments. By understanding its importance and implementing best practices, we can ensure the smooth and secure management of our infrastructure with Terraform.
