Define Lambda Function Configuration Variables

Lambda Function Configuration Variables

Lambda functions have several configurable parameters that benefit from variable definitions — especially when the same function module is used across environments with different resource allocations.

Variable Definitions

variable "lambda_runtime" {
  type        = string
  description = "Lambda function runtime"
  default     = "nodejs20.x"

  validation {
    condition     = contains(["nodejs18.x", "nodejs20.x", "python3.11", "python3.12", "go1.x", "java17", "java21"], var.lambda_runtime)
    error_message = "Must be a supported Lambda runtime."
  }
}

variable "lambda_memory" {
  type        = number
  description = "Memory allocated to the Lambda function in MB"
  default     = 256

  validation {
    condition     = var.lambda_memory >= 128 && var.lambda_memory <= 10240
    error_message = "Lambda memory must be between 128 MB and 10,240 MB."
  }
}

variable "lambda_timeout" {
  type        = number
  description = "Lambda function timeout in seconds"
  default     = 30

  validation {
    condition     = var.lambda_timeout >= 1 && var.lambda_timeout <= 900
    error_message = "Lambda timeout must be between 1 and 900 seconds."
  }
}

variable "lambda_env_vars" {
  type        = map(string)
  description = "Environment variables for the Lambda function"
  default     = {}
  sensitive   = true
}

Key Design Patterns

1. Runtime validation: The contains() check limits to supported runtimes, preventing deployment errors
2. Memory bounds: AWS Lambda supports 128 MB to 10,240 MB — the validation enforces these limits
3. Timeout bounds: Lambda max timeout is 900 seconds (15 minutes)
4. Sensitive env vars: Environment variables often contain API keys, so the entire map is marked sensitive

Environment-Specific Settings

# dev.tfvars
lambda_memory  = 128
lambda_timeout = 10
lambda_env_vars = {
  LOG_LEVEL = "debug"
  API_URL   = "https://api.dev.example.com"
}

# prod.tfvars
lambda_memory  = 1024
lambda_timeout = 60
lambda_env_vars = {
  LOG_LEVEL = "warn"
  API_URL   = "https://api.example.com"
}

Usage in Resource

resource "aws_lambda_function" "api" {
  function_name = "${var.project_name}-${var.environment}-api"
  runtime       = var.lambda_runtime
  memory_size   = var.lambda_memory
  timeout       = var.lambda_timeout

  environment {
    variables = var.lambda_env_vars
  }
}