When provisioning SSL/TLS certificates through AWS Certificate Manager (ACM) for CloudFront distributions, specifying a wildcard domain like *.example.com offers undeniable convenience. However, this approach comes with specific technical implications that architects should evaluate:

ACM doesn't charge extra for wildcard certificates - they're included in the free tier. However, indirect costs emerge from:

• Increased management complexity for multiple CloudFront distributions
• Potential over-provisioning of subdomains that may never be used
• Additional CloudFront distribution costs if you create separate instances for each subdomain

Wildcards introduce security considerations that often go unnoticed:

// Example of security policy that becomes harder to enforce
{
  "Version": "2012-10-17",
  "Statement": [
    {
      "Effect": "Deny",
      "Principal": "*",
      "Action": "cloudfront:CreateDistribution",
      "Resource": "arn:aws:cloudfront::123456789012:distribution/*",
      "Condition": {
        "StringNotLike": {
          "aws:RequestedRegion": ["us-east-1"],
          "aws:ResourceTag/Environment": ["production"]
        }
      }
    }
  ]
}

The certificate's broad coverage might lead to:

• Reduced certificate revocation granularity
• Increased attack surface if any subdomain gets compromised
• Potential compliance issues in regulated environments

Wildcard certificates in ACM create specific technical boundaries:

• Cannot be exported for use outside AWS ecosystem
• Limited to 100 fully qualified domain names per certificate
• Public certificates can't be used with EC2 instances directly

Here's how to programmatically check certificate coverage using AWS CLI:

#!/bin/bash
# Check if certificate covers specific domains
CERT_ARN=$(aws acm list-certificates --query 'CertificateSummaryList[?DomainName==example.com].CertificateArn' --output text)

DOMAINS_COVERED=$(aws acm describe-certificate --certificate-arn $CERT_ARN \
  --query 'Certificate.DomainValidationOptions[].DomainName' --output text)

if [[ $DOMAINS_COVERED == *"*.example.com"* ]]; then
  echo "Wildcard coverage confirmed"
else
  echo "No wildcard coverage found"
fi

• Use specific domains for production-critical services
• Reserve wildcards for development/staging environments
• Combine with AWS WAF for subdomain-specific protections
• Implement certificate expiration monitoring regardless of type

The decision ultimately depends on your specific use case. For temporary or development environments, wildcards provide excellent flexibility. For production systems handling sensitive data, more granular certificate management often proves worthwhile despite the additional configuration overhead.

When configuring SSL/TLS certificates in AWS Certificate Manager (ACM) for a domain like example.com, developers often face the decision between specific subdomains (www.example.com) versus wildcard certificates (*.example.com). While wildcards offer flexibility, there are technical implications worth examining.

Contrary to some assumptions, AWS ACM wildcard certificates don't incur additional costs. The pricing structure remains the same whether you request a single domain or wildcard certificate:

// ACM certificate request API call remains identical
aws acm request-certificate \
  --domain-name "example.com" \
  --subject-alternative-names "*.example.com" \
  --validation-method DNS

Wildcard certificates introduce several technical considerations:

• Certificate Validation Complexity: Wildcards require DNS validation for all potential subdomains
• Security Boundary Expansion: Compromise of any subdomain private key affects all subdomains
• CloudFront Distribution Limits: Each distribution still requires explicit domain specification

When integrating with CloudFront, the certificate usage remains similar but requires careful DNS configuration:

// CloudFormation snippet for CloudFront with wildcard
Resources:
  MyDistribution:
    Type: AWS::CloudFront::Distribution
    Properties:
      DistributionConfig:
        Aliases:
          - "www.example.com"
          - "blog.example.com"
        ViewerCertificate:
          AcmCertificateArn: !Ref MyWildcardCert
          SslSupportMethod: sni-only

For mission-critical applications, consider these patterns:

1. Use wildcards for development/test environments only
2. Implement separate certificates for production subdomains
3. Combine Route53 with ACM for automated certificate renewal
4. Monitor certificate expiration using CloudWatch Events

For organizations needing both flexibility and security:

// Terraform example for multiple specific certificates
resource "aws_acm_certificate" "primary" {
  domain_name       = "example.com"
  validation_method = "DNS"
  
  subject_alternative_names = [
    "www.example.com",
    "api.example.com"
  ]
}