AWS CloudFront CDN with Terraform - Complete Guide

resource "aws_cloudfront_distribution" "cdn" {
  origin {
    domain_name = aws_s3_bucket.website.bucket_regional_domain_name
    origin_id   = "S3"
    origin_access_control_id = aws_cloudfront_origin_access_control.main.id
  }
  enabled             = true
  default_root_object = "index.html"
  default_cache_behavior {
    allowed_methods        = ["GET", "HEAD"]
    cached_methods         = ["GET", "HEAD"]
    target_origin_id       = "S3"
    viewer_protocol_policy = "redirect-to-https"
    cache_policy_id        = "658327ea-f89d-4fab-a63d-7e88639e58f6"
  }
  viewer_certificate {
    cloudfront_default_certificate = true
  }
  restrictions {
    geo_restriction { restriction_type = "none" }
  }
}

resource "aws_cloudfront_origin_access_control" "main" {
  name                              = "${var.project}-oac"
  origin_access_control_origin_type = "s3"
  signing_behavior                  = "always"
  signing_protocol                  = "sigv4"
}
 
resource "aws_s3_bucket" "website" {
  bucket = "${var.project}-website"
}
 
resource "aws_s3_bucket_policy" "cdn" {
  bucket = aws_s3_bucket.website.id
  policy = jsonencode({
    Version = "2012-10-17"
    Statement = [{
      Sid       = "AllowCloudFront"
      Effect    = "Allow"
      Principal = { Service = "cloudfront.amazonaws.com" }
      Action    = "s3:GetObject"
      Resource  = "${aws_s3_bucket.website.arn}/*"
      Condition = {
        StringEquals = {
          "AWS:SourceArn" = aws_cloudfront_distribution.cdn.arn
        }
      }
    }]
  })
}

resource "aws_cloudfront_distribution" "cdn" {
  origin {
    domain_name              = aws_s3_bucket.website.bucket_regional_domain_name
    origin_id                = "S3Origin"
    origin_access_control_id = aws_cloudfront_origin_access_control.main.id
  }
 
  enabled             = true
  is_ipv6_enabled     = true
  default_root_object = "index.html"
  aliases             = [var.domain_name]
  price_class         = "PriceClass_100"  # US, Canada, Europe only
 
  default_cache_behavior {
    allowed_methods        = ["GET", "HEAD", "OPTIONS"]
    cached_methods         = ["GET", "HEAD"]
    target_origin_id       = "S3Origin"
    viewer_protocol_policy = "redirect-to-https"
    compress               = true
 
    cache_policy_id          = aws_cloudfront_cache_policy.static.id
    origin_request_policy_id = null
  }
 
  custom_error_response {
    error_code         = 404
    response_code      = 404
    response_page_path = "/404.html"
  }
 
  custom_error_response {
    error_code         = 403
    response_code      = 404
    response_page_path = "/404.html"
  }
 
  viewer_certificate {
    acm_certificate_arn      = aws_acm_certificate.main.arn
    ssl_support_method       = "sni-only"
    minimum_protocol_version = "TLSv1.2_2021"
  }
 
  restrictions {
    geo_restriction {
      restriction_type = "none"
    }
  }
 
  tags = { Environment = var.environment }
}

resource "aws_cloudfront_cache_policy" "static" {
  name        = "${var.project}-static-cache"
  default_ttl = 86400    # 1 day
  max_ttl     = 31536000 # 1 year
  min_ttl     = 0
 
  parameters_in_cache_key_and_forwarded_to_origin {
    cookies_config {
      cookie_behavior = "none"
    }
    headers_config {
      header_behavior = "none"
    }
    query_strings_config {
      query_string_behavior = "none"
    }
    enable_accept_encoding_gzip   = true
    enable_accept_encoding_brotli = true
  }
}

provider "aws" {
  alias  = "us_east_1"
  region = "us-east-1"
}
 
resource "aws_acm_certificate" "main" {
  provider          = aws.us_east_1
  domain_name       = var.domain_name
  validation_method = "DNS"
 
  subject_alternative_names = ["*.${var.domain_name}"]
 
  lifecycle {
    create_before_destroy = true
  }
}
 
resource "aws_route53_record" "cert_validation" {
  for_each = {
    for dvo in aws_acm_certificate.main.domain_validation_options : dvo.domain_name => dvo
  }
  zone_id = aws_route53_zone.main.zone_id
  name    = each.value.resource_record_name
  type    = each.value.resource_record_type
  records = [each.value.resource_record_value]
  ttl     = 60
}
 
resource "aws_acm_certificate_validation" "main" {
  provider                = aws.us_east_1
  certificate_arn         = aws_acm_certificate.main.arn
  validation_record_fqdns = [for r in aws_route53_record.cert_validation : r.fqdn]
}

resource "aws_cloudfront_distribution" "api" {
  origin {
    domain_name = aws_lb.main.dns_name
    origin_id   = "ALBOrigin"
 
    custom_origin_config {
      http_port              = 80
      https_port             = 443
      origin_protocol_policy = "https-only"
      origin_ssl_protocols   = ["TLSv1.2"]
    }
  }
 
  default_cache_behavior {
    allowed_methods        = ["DELETE", "GET", "HEAD", "OPTIONS", "PATCH", "POST", "PUT"]
    cached_methods         = ["GET", "HEAD"]
    target_origin_id       = "ALBOrigin"
    viewer_protocol_policy = "redirect-to-https"
 
    cache_policy_id          = "4135ea2d-6df8-44a3-9df3-4b5a84be39ad" # CachingDisabled
    origin_request_policy_id = "216adef6-5c7f-47e4-b989-5492eafa07d3" # AllViewer
  }
}