Dynamic blocks in Terraform are a powerful feature that allows you to generate repeated nested blocks within resources, data sources, providers, and provisioners based on complex data structures. They provide a way to programmatically create multiple similar configuration blocks using iteration.
T…Dynamic blocks in Terraform are a powerful feature that allows you to generate repeated nested blocks within resources, data sources, providers, and provisioners based on complex data structures. They provide a way to programmatically create multiple similar configuration blocks using iteration.
The syntax for a dynamic block includes the 'dynamic' keyword followed by a label that represents the type of nested block you want to generate. Inside, you use a 'for_each' argument to specify the collection to iterate over, and a 'content' block that defines the structure of each generated nested block.
Here's the basic structure:
dynamic "block_name" {
for_each = var.collection
content {
attribute = block_name.value.some_property
}
}
Within the content block, you can access the current iteration using the iterator variable, which defaults to the dynamic block's label. You can customize this with the 'iterator' argument. The iterator object provides two attributes: 'key' (the index or map key) and 'value' (the current element).
Dynamic blocks are particularly useful when working with resources that require multiple similar nested configurations, such as AWS security group rules, Azure network security rules, or GCP firewall rules. Instead of manually writing each nested block, you can define them in a variable and let Terraform generate the appropriate configuration.
Best practices include using dynamic blocks sparingly to maintain code readability, providing clear variable structures, and documenting the expected input format. Overusing dynamic blocks can make configurations harder to understand and debug.
Common use cases include:
- Security group ingress/egress rules
- Load balancer listeners and target groups
- IAM policy statements
- Storage lifecycle rules
Dynamic blocks help reduce code duplication and make Terraform configurations more maintainable by centralizing repeated patterns into data-driven definitions, enabling infrastructure as code to be more flexible and scalable.
Dynamic Blocks in Terraform: Complete Guide
What are Dynamic Blocks?
Dynamic blocks are a special Terraform feature that allows you to generate multiple nested blocks within a resource, data source, provider, or provisioner based on a collection or expression. They provide a way to create repetitive nested configuration blocks programmatically rather than writing them out manually.
Why Dynamic Blocks are Important
Dynamic blocks solve a critical problem in Terraform configurations:
1. Reducing Code Duplication: When you need multiple similar nested blocks (like multiple ingress rules in a security group), dynamic blocks eliminate repetitive code.
2. Flexibility: They allow configurations to adapt based on variable inputs, making modules more reusable.
3. Maintainability: Changes to repeated configurations only need to be made in one place.
4. Scalability: Easily handle scenarios where the number of nested blocks is unknown until runtime.
How Dynamic Blocks Work
The syntax for a dynamic block includes:
dynamic "block_name" { for_each = collection content { # block arguments using block_name.key and block_name.value }}
Key Components:
- dynamic: The keyword that starts the block - block_name: The label matching the nested block type you want to generate - for_each: The collection to iterate over (list, set, or map) - content: The nested block that defines the body of each generated block - iterator: Optional argument to change the name of the temporary variable (defaults to the block name)
- Dynamic blocks can only generate arguments that belong to the resource type being configured - Overusing dynamic blocks can make configurations harder to read - They should be used when dealing with collections of similar nested blocks - Dynamic blocks can be nested within each other for complex scenarios
Exam Tips: Answering Questions on Dynamic Blocks
1. Remember the Required Arguments: The for_each and content arguments are mandatory in every dynamic block.
2. Know the Default Iterator Name: If no iterator is specified, the iterator name defaults to the dynamic block label name.
3. Understand the Object Properties: Each iterator object has two properties: key (the map key or list index) and value (the value at that key/index).
4. Recognize Valid Use Cases: Dynamic blocks are used for nested blocks within resources, not for creating multiple resources (use for_each or count for that).
5. Syntax Recognition: Be able to identify correct dynamic block syntax and spot errors in malformed examples.
6. Content Block Requirement: Always remember that the actual configuration goes inside the content block, not at the dynamic block level.
7. Collection Types: The for_each argument accepts lists, sets, and maps - know how each affects the iterator values.
8. Distinguish from for_each: Dynamic blocks handle nested blocks, while resource-level for_each creates multiple resource instances.