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Terraform

Terraform API Gateway: Variables in Request Paths

By Filip on 10/07/2024

Learn how to dynamically define API Gateway endpoint paths in Terraform using variables for flexible and reusable infrastructure deployments.

Terraform API Gateway: Variables in Request Paths

Table of Contents

Introduction

This guide explains how to define an API Gateway endpoint in Terraform with a variable path part, allowing you to create flexible and dynamic API endpoints.

Step-by-Step Guide

To define an API Gateway endpoint in Terraform with a variable path part, you'll need to utilize the aws_api_gateway_resource resource. This resource allows you to specify a path_part attribute, which can be set to the variable you want to use in your endpoint path.

For example, if you want an endpoint like /accounts/{account_id}, you would define an aws_api_gateway_resource with a path_part of accounts and then another aws_api_gateway_resource with a path_part of {account_id}. This {account_id} acts as a placeholder and will be replaced with the actual account ID when a request is made.

Remember that changes to resources like aws_api_gateway_integration, especially the request_template property, might not automatically trigger an update in aws_api_gateway_deployment. You might need to manually redeploy the API Gateway stage or introduce a dependency to ensure updates are reflected.

When working with Lambda proxy integrations, you can access the path variables within your Lambda function using API Gateway mapping templates. These templates use a specific syntax to reference variables like method.request.path.accountId to retrieve the value captured by the {account_id} path part.

For managing multiple path parts in your API Gateway configuration, using Terraform modules can help organize your code and make it more reusable. You can define variables within your module for different path parts and then reference them when creating your API Gateway resources.

Finally, always refer to the official Terraform documentation for the aws_api_gateway_resource and aws_api_gateway_integration resources for the most up-to-date information on available attributes and usage examples.

Code Example

This Terraform code sets up an API Gateway REST API with a variable path part for accessing resources by ID. It integrates a GET method with a Lambda function using a proxy integration. The code includes a placeholder for the Lambda function, deployment configuration, and an output for the API Gateway invoke URL.

# Configure the AWS Provider
terraform {
  required_providers {
    aws = {
      source  = "hashicorp/aws"
      version = "~> 4.0" # Adjust version as needed
    }
  }
}

# Configure variables for reusability
variable "api_gateway_name" {
  type = string
  default = "my-api-gateway"
}

variable "lambda_function_name" {
  type = string
  default = "my-lambda-function"
}

# Create an API Gateway REST API
resource "aws_api_gateway_rest_api" "example" {
  name        = var.api_gateway_name
}

# Create a root resource
resource "aws_api_gateway_resource" "root" {
  rest_api_id = aws_api_gateway_rest_api.example.id
  parent_id   = aws_api_gateway_rest_api.example.root_resource_id
  path_part   = "accounts"
}

# Create a resource with a variable path part
resource "aws_api_gateway_resource" "account_id" {
  rest_api_id = aws_api_gateway_rest_api.example.id
  parent_id   = aws_api_gateway_resource.root.id
  path_part   = "{account_id}"
}

# Create a GET method on the resource with the variable path part
resource "aws_api_gateway_method" "get" {
  rest_api_id   = aws_api_gateway_rest_api.example.id
  resource_id   = aws_api_gateway_resource.account_id.id
  http_method   = "GET"
  authorization = "NONE"
}

# Integrate the method with a Lambda function
resource "aws_api_gateway_integration" "integration" {
  rest_api_id             = aws_api_gateway_rest_api.example.id
  resource_id             = aws_api_gateway_resource.account_id.id
  http_method             = aws_api_gateway_method.get.http_method
  integration_http_method = "POST"
  type                    = "AWS_PROXY"
  integration_uri         = aws_lambda_function.example.invoke_arn
}

# Create a Lambda function (replace with your actual function)
resource "aws_lambda_function" "example" {
  function_name = var.lambda_function_name
  # ... other Lambda function configuration ...
}

# Create a deployment to make the changes live
resource "aws_api_gateway_deployment" "example" {
  rest_api_id = aws_api_gateway_rest_api.example.id
  # This dependency ensures the deployment happens after changes to the integration
  depends_on = [aws_api_gateway_integration.integration]
}

# Create an API Gateway stage
resource "aws_api_gateway_stage" "example" {
  stage_name        = "prod"
  rest_api_id      = aws_api_gateway_rest_api.example.id
  deployment_id   = aws_api_gateway_deployment.example.id
}

# Output the API Gateway endpoint URL
output "api_gateway_invoke_url" {
  value = "${aws_api_gateway_stage.example.invoke_url}/accounts/{account_id}"
}

Explanation:

  1. API Gateway Setup: The code defines an API Gateway REST API with a root resource (/accounts) and a child resource with a variable path part (/{account_id}).
  2. Method and Integration: A GET method is created on the /accounts/{account_id} resource and integrated with a Lambda function using a proxy integration.
  3. Lambda Function: A placeholder for your Lambda function is included. You'll need to replace this with your actual function code and configuration.
  4. Deployment and Stage: A deployment is created to publish the API Gateway changes, and a stage (prod) is created to make the API accessible.
  5. Output: The output variable api_gateway_invoke_url provides the base URL for invoking your API, including the variable path part.

Key Points:

  • Variable Path Part: The {account_id} in the path_part attribute of the aws_api_gateway_resource resource defines the variable segment in your API endpoint.
  • Lambda Integration: The aws_api_gateway_integration resource sets up the proxy integration with your Lambda function.
  • Deployment Dependency: The depends_on meta-argument in aws_api_gateway_deployment ensures that the deployment happens after changes to the integration.
  • Accessing Path Variables: Inside your Lambda function, you can access the value of account_id using the API Gateway mapping template syntax, such as method.request.path.accountId.

Remember:

  • Replace the placeholder Lambda function with your actual function code.
  • Configure the API Gateway authorization, request validation, and other settings as needed for your use case.
  • Refer to the official Terraform documentation for detailed information on the resources and attributes used in this example.

Additional Notes

  • Resource Naming: Use descriptive names for your API Gateway resources (aws_api_gateway_resource) to improve code readability. For instance, instead of "root", a name like "accounts_root" would be clearer.
  • Error Handling: Consider adding error handling logic to your Lambda function and configuring appropriate API Gateway responses for different error scenarios.
  • API Gateway Stages: Utilize different API Gateway stages (e.g., "dev", "test", "prod") to manage different environments and promote changes gradually.
  • Versioning: Implement API versioning in your path structure (e.g., /v1/accounts/{account_id}) to maintain backward compatibility as your API evolves.
  • Security: Don't forget to secure your API Gateway endpoints using authentication and authorization mechanisms like API keys, IAM roles, or Lambda authorizers.
  • Request Validation: Use API Gateway request validation to enforce data types, formats, and constraints on incoming requests to your API.
  • Terraform State: Securely store your Terraform state file to track your infrastructure configuration and enable collaboration within your team.
  • Testing: Thoroughly test your API Gateway endpoints, including variable path parts, using tools like Postman or curl to ensure they function as expected.
  • Monitoring: Set up monitoring and logging for your API Gateway and Lambda functions to track performance, identify errors, and gain insights into API usage.
  • Documentation: Document your API endpoints, including variable path parts and expected input/output, to help consumers understand and integrate with your API.

Summary

This article provides a concise guide on using Terraform to define API Gateway endpoints with variable path parts.

Key Takeaways:

  • aws_api_gateway_resource: This resource is crucial for defining variable paths. The path_part attribute allows you to specify static segments and placeholders (e.g., {account_id}) for dynamic values.
  • Placeholder Resolution: Placeholders in the path are replaced with actual values during request processing.
  • Manual Deployment Trigger: Changes to resources like aws_api_gateway_integration might not automatically trigger a deployment. Manual redeployment or dependency management might be necessary.
  • Lambda Integration and Mapping Templates: When using Lambda proxy integrations, API Gateway mapping templates allow you to access path variables within your Lambda function using a specific syntax (e.g., method.request.path.accountId).
  • Terraform Modules for Organization: For complex API Gateway configurations with multiple path parts, using Terraform modules can enhance code organization and reusability.
  • Official Documentation: Always consult the official Terraform documentation for the latest information on aws_api_gateway_resource and aws_api_gateway_integration resources.

Conclusion

By leveraging the aws_api_gateway_resource resource and its path_part attribute, Terraform empowers you to define API Gateway endpoints with variable path parts. This capability enables the creation of flexible and dynamic APIs that handle a wide range of requests. Remember to consider manual deployment triggers, utilize Lambda mapping templates for accessing path variables in your functions, and explore Terraform modules for managing complex API Gateway configurations. Always refer to the official Terraform documentation for the most up-to-date information on the resources and their attributes. By following these best practices, you can effectively design, deploy, and manage robust APIs using Terraform and AWS API Gateway.

References

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