Infrastructure as Code Patterns

What are the key principles and patterns of Infrastructure as Code? How do you structure IaC for multiple environments?

Infrastructureintermediate

// interview question

What are the key principles and patterns of Infrastructure as Code? How do you structure IaC for multiple environments?

Sample answer

Key IaC principles: declarative over imperative, idempotent operations, version control everything, and immutable infrastructure. For multiple environments, use modules for reusable components, separate state files per environment, use workspaces or directory structures (dev/staging/prod), parameterize with variables and tfvars files, and implement DRY (Don't Repeat Yourself) through modules. Always test changes in lower environments first.

Why this matters

IaC is the foundation of modern DevOps practices. Well-structured IaC enables reproducible infrastructure, reduces configuration drift, facilitates disaster recovery, and allows infrastructure changes to go through the same code review process as application code.

Code examples

Terraform module structure

hcl

# Directory structure:
# infrastructure/
#   modules/
#     vpc/
#     eks/
#   environments/
#     dev/
#       main.tf
#       terraform.tfvars
#     prod/
#       main.tf
#       terraform.tfvars

# environments/dev/main.tf
module "vpc" {
  source = "../../modules/vpc"
  
  environment = var.environment
  cidr_block  = var.vpc_cidr
}

module "eks" {
  source = "../../modules/eks"
  
  vpc_id      = module.vpc.vpc_id
  subnet_ids  = module.vpc.private_subnet_ids
  environment = var.environment
}

Common mistakes to avoid

Hardcoding environment-specific values
Not using remote state with locking
Creating overly complex module hierarchies

Likely follow-ups

How do you handle secrets in Infrastructure as Code?
What is the difference between Terraform workspaces and directory-based separation?
How do you test infrastructure code before applying?

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