Terraform: Creating Resources Before Destroying Them
In the realm of infrastructure as code (IaC), Terraform reigns supreme. It empowers you to manage your cloud infrastructure efficiently, using declarative configurations to define your desired state. However, a common challenge arises when you need to update resources. The natural inclination is to destroy the old version and create a new one. This is where the "terraform create before destroy" strategy shines.
Why Create Before Destroy?
What if you need to maintain continuity? Imagine managing a production environment with sensitive data residing in a database. Destroying and recreating the database could lead to data loss. This is where the "create before destroy" principle becomes crucial. By creating the new version of a resource before destroying the old one, you ensure smooth transitions and minimize downtime.
The "create before destroy" Strategy in Action
Let's consider a practical scenario: You want to upgrade a virtual machine instance to a new version. Instead of instantly replacing the old instance, you can utilize Terraform's capabilities to create the new instance first, configure it, and only then tear down the outdated one. This approach ensures seamless migration and avoids service interruptions.
Implementing "create before destroy" with Terraform
Terraform allows you to implement this strategy effectively using various techniques.
1. Utilizing lifecycle blocks: The lifecycle block in your Terraform configuration provides granular control over resource creation and destruction. You can leverage the create_before_destroy option to specify that the new resource should be created before the old one is destroyed.
Example:
resource "aws_instance" "example" {
# ... other instance attributes
lifecycle {
create_before_destroy = true
}
}
2. Using the depends_on meta-argument: The depends_on meta-argument allows you to define dependencies between resources. You can create a dependency where a new resource must be created before destroying the old one.
Example:
resource "aws_instance" "old" {
# ... old instance attributes
}
resource "aws_instance" "new" {
# ... new instance attributes
depends_on = [aws_instance.old]
}
Benefits of the "create before destroy" Strategy
- Zero downtime: This method minimizes downtime during upgrades or updates by creating the new resource first.
- Data preservation: For resources like databases, this strategy ensures that data remains intact during updates.
- Rollback capability: If anything goes wrong with the new resource, you can roll back to the old resource without losing data.
Considerations for the "create before destroy" Approach
- Increased resource consumption: Creating a new resource before destroying the old one temporarily increases resource consumption.
- Complexity: Implementing "create before destroy" might add complexity to your Terraform configuration.
- Not suitable for all scenarios: This approach might not be ideal for all resources, particularly those where creation and destruction are quick and effortless.
Conclusion
The "terraform create before destroy" strategy offers a powerful way to manage resource updates in Terraform. It prioritizes data preservation and minimal downtime, making it a crucial technique for sensitive environments. By understanding this approach and its implementation, you can effectively navigate resource updates in Terraform, ensuring smooth transitions and minimizing disruptions to your infrastructure.