DNS A Record Implementation Guide

TL;DR: A records map domain names to IPv4 addresses, forming the DNS foundation that enables HTTP-01 ACME challenges, web services, and certificate validation. Proper A record implementation requires understanding apex vs subdomain patterns, TTL strategies, Infrastructure-as-Code management, and geographic distribution for global certificate operations.

Overview: DNS Infrastructure for ACME Automation

A records represent the most essential DNS record type—without them, domain names cannot resolve to servers, and ACME HTTP-01 challenges cannot complete. While conceptually straightforward (domain → IP address), production A record implementations involve complex considerations: split-brain DNS for multi-region deployments, TTL optimization for migration windows, Infrastructure-as-Code management for consistency, and geographic distribution for global certificate automation.

The implementation challenge: Modern organizations operate certificates across dozens of domains, multiple cloud regions, and diverse infrastructure—containers, VMs, serverless, edge computing. Each requires correct A record configuration for ACME validation, but different infrastructure types demand different A record patterns. A record implementation strategy that works for a single-server deployment breaks completely in multi-cloud, globally distributed environments.

Why This Belongs in ACME Client Operations

This guide complements A Record Configuration by focusing on implementation patterns rather than operational troubleshooting. While the configuration guide addresses "why is my ACME validation failing," this guide addresses "how should I architect A records for scalable ACME automation."

Different focus areas:

A Record Configuration (operational troubleshooting): - Debugging HTTP-01 validation failures - CDN/proxy complications with ACME - Load balancer challenge routing - Common misconfigurations breaking ACME

DNS A Record Implementation (this page, infrastructure patterns): - Infrastructure-as-Code A record management - Multi-region geographic distribution - TTL strategies for different environments - Enterprise automation and consistency - Public Suffix List considerations for dynamic DNS

Real-world implementation scenario: Your organization operates ACME automation across 3 AWS regions, 2 Azure regions, and on-premises infrastructure. Each region has separate certificate servers for latency optimization. You need A record implementation patterns that support: - Regional subdomains for latency optimization (us-east.api.example.com, eu-west.api.example.com) - Consistent A record TTLs across all environments - Infrastructure-as-Code for reproducible deployments - Automated A record creation/updates during infrastructure scaling - Health-check-based failover without manual DNS updates

Related Documentation

This page is part of the Operating ACME Clients section:

• Operating ACME Clients Overview - Section introduction
• X.509 Certificate Verification - Certificate validation
• Certbot Renewal Automation - Renewal automation
• DNS-01 Challenge Validation - DNS-based validation
• A Record Configuration - ACME-specific A record troubleshooting
• DNS A Record Implementation (this page) - Infrastructure patterns
• HTTP-01 Challenge Validation (coming) - HTTP-01 requiring proper A records

For infrastructure context: - Multi-Cloud PKI - Certificates across cloud providers - Certificate-as-Code - Infrastructure-as-Code patterns - High Availability & Disaster Recovery - Failover patterns

---

Problem Statement

Common A record implementation challenges in enterprise ACME environments include:

• Split-brain configurations where apex and www subdomains point to different infrastructure (intentional or accidental)
• Missing subdomain records causing HTTP-01 certificate validation failures for services assumed to be covered
• DNS propagation delays affecting service availability during infrastructure migrations and certificate reissuance
• Inconsistent TTL values leading to caching issues across global CDN and resolver infrastructure
• Public Suffix List complications with dynamic DNS services (DuckDNS, No-IP) and NAS devices (Synology, QNAP)
• Infrastructure-as-Code drift where manually created A records diverge from Terraform/CloudFormation definitions
• Multi-region complexity requiring geographic A record distribution for latency optimization

Enterprise failure scenario: Your organization manages 50+ domains across AWS, Azure, and GCP. Manual A record management leads to inconsistent configurations—some domains have www records, others don't. Some use TTL 300, others 86400. During a certificate renewal, HTTP-01 challenges fail intermittently because DNS caching causes some regions to resolve to old IPs from a previous migration. Debugging requires checking 50 domains × 3 DNS providers × 4 public resolvers = 600 manual checks.

Architecture

Standard A Record Structure

domain.com.     TTL    IN    A    192.0.2.1
www.domain.com. TTL    IN    A    192.0.2.1

Field Breakdown: - domain.com.: Fully Qualified Domain Name (trailing dot = absolute) - TTL: Time-to-live in seconds (cache duration) - IN: Internet class (standard for all DNS records) - A: IPv4 address record type (vs AAAA for IPv6) - 192.0.2.1: Target IPv4 address

Enterprise DNS Hierarchy

┌─ Authoritative DNS Server (ns1.example.com)
│
├─ Zone File Management (example.com zone)
│  │
│  ├─ Apex Domain (@, example.com)
│  │  └─ A record → 203.0.113.10
│  │
│  ├─ WWW Subdomain (www.example.com)
│  │  └─ A record → 203.0.113.10
│  │
│  ├─ Service Subdomains
│  │  ├─ mail.example.com → 203.0.113.20
│  │  ├─ api.example.com → 203.0.113.30
│  │  └─ vpn.example.com → 203.0.113.40
│  │
│  └─ Geographic Subdomains
│     ├─ us-east.api.example.com → 203.0.113.31
│     ├─ eu-west.api.example.com → 198.51.100.10
│     └─ ap-south.api.example.com → 192.0.2.10
│
└─ TTL Strategy by Record Type
   ├─ Production services: 300-1800s
   ├─ Static infrastructure: 3600-7200s
   └─ Migration/testing: 60-300s

Load Balancer Integration for High Availability

For high-availability ACME setups with multiple backend servers:

# Round-robin DNS (simple load distribution)
api.domain.com.     300    IN    A    10.0.1.10
api.domain.com.     300    IN    A    10.0.1.11
api.domain.com.     300    IN    A    10.0.1.12

# All servers must serve identical ACME challenges
# Otherwise: 66% validation failure rate

Better Approach: Single A record to load balancer VIP

api.domain.com.     300    IN    A    10.0.1.100  # Load balancer VIP

# Load balancer routes /.well-known/acme-challenge/ to certificate server

Implementation

1. Basic A Record Creation

BIND Zone File (Traditional DNS)

$ORIGIN domain.com.
$TTL 300

; Apex domain
@               IN    A    203.0.113.10

; WWW subdomain
www             IN    A    203.0.113.10

; Service-specific
mail            IN    A    203.0.113.20
api             IN    A    203.0.113.30

AWS Route 53 CLI

# Create A record for apex domain
aws route53 change-resource-record-sets \
  --hosted-zone-id Z1234567890ABC \
  --change-batch '{
    "Changes": [{
      "Action": "CREATE",
      "ResourceRecordSet": {
        "Name": "example.com",
        "Type": "A",
        "TTL": 300,
        "ResourceRecords": [{"Value": "203.0.113.10"}]
      }
    }]
  }'

# Create A record for www subdomain
aws route53 change-resource-record-sets \
  --hosted-zone-id Z1234567890ABC \
  --change-batch '{
    "Changes": [{
      "Action": "CREATE",
      "ResourceRecordSet": {
        "Name": "www.example.com",
        "Type": "A",
        "TTL": 300,
        "ResourceRecords": [{"Value": "203.0.113.10"}]
      }
    }]
  }'

Cloudflare API

ZONE_ID="your-zone-id"
API_TOKEN="your-api-token"

# Create apex A record
curl -X POST "https://api.cloudflare.com/client/v4/zones/$ZONE_ID/dns_records" \
  -H "Authorization: Bearer $API_TOKEN" \
  -H "Content-Type: application/json" \
  --data '{
    "type": "A",
    "name": "@",
    "content": "203.0.113.10",
    "ttl": 300,
    "proxied": false
  }'

# Create www A record
curl -X POST "https://api.cloudflare.com/client/v4/zones/$ZONE_ID/dns_records" \
  -H "Authorization: Bearer $API_TOKEN" \
  -H "Content-Type: application/json" \
  --data '{
    "type": "A",
    "name": "www",
    "content": "203.0.113.10",
    "ttl": 300,
    "proxied": false
  }'

Azure DNS CLI

# Create A record for apex
az network dns record-set a add-record \
  --resource-group MyResourceGroup \
  --zone-name example.com \
  --record-set-name @ \
  --ipv4-address 203.0.113.10 \
  --ttl 300

# Create A record for www
az network dns record-set a add-record \
  --resource-group MyResourceGroup \
  --zone-name example.com \
  --record-set-name www \
  --ipv4-address 203.0.113.10 \
  --ttl 300

2. Certificate Validation Requirements

For Let's Encrypt HTTP-01 challenges, both apex and www must resolve:

# Minimum requirement for ACME HTTP-01
example.com.        300    IN    A    server_ip
www.example.com.    300    IN    A    server_ip

# Verification
dig +short example.com @8.8.8.8
dig +short www.example.com @8.8.8.8

# Both should return same IP for consistent certificate coverage

Multi-SAN Certificate Considerations:

# Certificate for: example.com, www.example.com, blog.example.com
# All domains need A records pointing to validation server

example.com.        300    IN    A    203.0.113.10
www.example.com.    300    IN    A    203.0.113.10
blog.example.com.   300    IN    A    203.0.113.10

# Certbot will validate all three during issuance
certbot certonly --nginx \
  -d example.com \
  -d www.example.com \
  -d blog.example.com

3. Enterprise Automation with Infrastructure-as-Code

Terraform Configuration (Multi-Provider)

Cloudflare Provider:

terraform {
  required_providers {
    cloudflare = {
      source = "cloudflare/cloudflare"
      version = "~> 4.0"
    }
  }
}

provider "cloudflare" {
  api_token = var.cloudflare_api_token
}

# Variables
variable "server_ip" {
  description = "Web server IP address"
  type        = string
  default     = "203.0.113.10"
}

variable "zone_id" {
  description = "Cloudflare zone ID"
  type        = string
}

# Apex domain A record
resource "cloudflare_record" "apex" {
  zone_id = var.zone_id
  name    = "@"
  value   = var.server_ip
  type    = "A"
  ttl     = 300
  proxied = false  # Disable proxy for ACME validation
}

# WWW subdomain A record
resource "cloudflare_record" "www" {
  zone_id = var.zone_id
  name    = "www"
  value   = var.server_ip
  type    = "A"
  ttl     = 300
  proxied = false
}

# API subdomain
resource "cloudflare_record" "api" {
  zone_id = var.zone_id
  name    = "api"
  value   = var.api_server_ip
  type    = "A"
  ttl     = 300
  proxied = false
}

AWS Route53 Provider:

provider "aws" {
  region = "us-east-1"
}

data "aws_route53_zone" "primary" {
  name = "example.com"
}

# Apex A record
resource "aws_route53_record" "apex" {
  zone_id = data.aws_route53_zone.primary.zone_id
  name    = "example.com"
  type    = "A"
  ttl     = 300
  records = [var.server_ip]
}

# WWW A record
resource "aws_route53_record" "www" {
  zone_id = data.aws_route53_zone.primary.zone_id
  name    = "www.example.com"
  type    = "A"
  ttl     = 300
  records = [var.server_ip]
}

# Output for verification
output "apex_ip" {
  value = aws_route53_record.apex.records[0]
}

output "www_ip" {
  value = aws_route53_record.www.records[0]
}

Multi-Cloud Terraform Pattern:

# Manage DNS across multiple providers
module "cloudflare_dns" {
  source = "./modules/cloudflare-dns"
  domains = {
    "example.com" = "203.0.113.10"
    "api.example.com" = "203.0.113.20"
  }
}

module "route53_dns" {
  source = "./modules/route53-dns"
  domains = {
    "aws-service.example.com" = "54.xxx.xxx.xxx"
  }
}

module "azure_dns" {
  source = "./modules/azure-dns"
  domains = {
    "azure-app.example.com" = "20.xxx.xxx.xxx"
  }
}

Ansible Playbook for A Record Management

---
- name: Configure A records for ACME infrastructure
  hosts: localhost
  vars:
    dns_records:
      - name: "@"
        type: "A"
        value: "{{ server_ip }}"
        ttl: 300
      - name: "www"
        type: "A"
        value: "{{ server_ip }}"
        ttl: 300
      - name: "api"
        type: "A"
        value: "{{ api_server_ip }}"
        ttl: 300

  tasks:
    - name: Create A records in Cloudflare
      cloudflare_dns:
        zone: example.com
        record: "{{ item.name }}"
        type: "{{ item.type }}"
        value: "{{ item.value }}"
        ttl: "{{ item.ttl }}"
        proxied: false
        api_token: "{{ cloudflare_api_token }}"
      loop: "{{ dns_records }}"

    - name: Verify A record resolution
      command: dig +short {{ item.name }}.example.com @8.8.8.8
      register: dns_check
      loop: "{{ dns_records }}"

    - name: Display DNS verification results
      debug:
        msg: "{{ item.item.name }}.example.com → {{ item.stdout }}"
      loop: "{{ dns_check.results }}"

Python DNS Automation

import CloudFlare
import boto3

class DNSRecordManager:
    """Manage A records across multiple DNS providers for ACME infrastructure"""

    def __init__(self, cloudflare_token=None, aws_profile=None):
        self.cf = CloudFlare.CloudFlare(token=cloudflare_token) if cloudflare_token else None
        self.r53 = boto3.client('route53', profile_name=aws_profile) if aws_profile else None

    def create_a_record_cloudflare(self, zone_id, name, ip, ttl=300):
        """Create A record in Cloudflare"""
        try:
            record = self.cf.zones.dns_records.post(
                zone_id,
                data={
                    'type': 'A',
                    'name': name,
                    'content': ip,
                    'ttl': ttl,
                    'proxied': False  # Required for ACME HTTP-01
                }
            )
            print(f"Created: {name} → {ip}")
            return record
        except CloudFlare.exceptions.CloudFlareAPIError as e:
            print(f"Error: {e}")
            return None

    def create_a_record_route53(self, zone_id, name, ip, ttl=300):
        """Create A record in Route53"""
        try:
            response = self.r53.change_resource_record_sets(
                HostedZoneId=zone_id,
                ChangeBatch={
                    'Changes': [{
                        'Action': 'UPSERT',
                        'ResourceRecordSet': {
                            'Name': name,
                            'Type': 'A',
                            'TTL': ttl,
                            'ResourceRecords': [{'Value': ip}]
                        }
                    }]
                }
            )
            print(f"Created: {name} → {ip}")
            return response
        except Exception as e:
            print(f"Error: {e}")
            return None

    def validate_a_records(self, domains):
        """Verify A records resolve correctly"""
        import dns.resolver

        results = {}
        for domain in domains:
            try:
                answers = dns.resolver.resolve(domain, 'A')
                results[domain] = [str(rdata) for rdata in answers]
            except Exception as e:
                results[domain] = f"Error: {e}"

        return results

# Usage
manager = DNSRecordManager(cloudflare_token="your-token")
manager.create_a_record_cloudflare(
    zone_id="zone123",
    name="www",
    ip="203.0.113.10"
)

4. Validation and Testing

Comprehensive DNS Testing Script

#!/bin/bash
# Validate A record configuration for ACME readiness

DOMAIN="$1"
EXPECTED_IP="$2"

echo "=== A Record Validation for ACME Infrastructure ==="
echo "Domain: $DOMAIN"
echo "Expected IP: $EXPECTED_IP"
echo ""

# Test against multiple public DNS resolvers
RESOLVERS=("8.8.8.8" "8.8.4.4" "1.1.1.1" "1.0.0.1" "208.67.222.222" "208.67.220.220")

echo "Checking A record resolution across public DNS:"
MISMATCH=0
for resolver in "${RESOLVERS[@]}"; do
  ip=$(dig +short "$DOMAIN" @"$resolver" | grep -E '^[0-9]+\.' | head -n1)

  if [ "$ip" == "$EXPECTED_IP" ]; then
    echo "  ✓ $resolver → $ip"
  else
    echo "  ✗ $resolver → $ip (expected $EXPECTED_IP)"
    MISMATCH=1
  fi
done

if [ $MISMATCH -eq 1 ]; then
  echo ""
  echo "WARNING: DNS propagation incomplete or A record misconfigured"
  echo "Wait for propagation or fix A record"
  exit 1
fi

echo ""
echo "✓ All resolvers return consistent IP: $EXPECTED_IP"
echo ""

# Test HTTP connectivity for ACME HTTP-01
echo "Testing HTTP connectivity (ACME HTTP-01 requirement):"
if timeout 5 curl -sf -o /dev/null -w "%{http_code}" "http://$DOMAIN/.well-known/acme-challenge/test" | grep -q "404\|200"; then
  echo "  ✓ HTTP server reachable on $DOMAIN"
  echo "  ✓ ACME HTTP-01 validation should succeed"
else
  echo "  ✗ Cannot reach HTTP server on $DOMAIN"
  echo "  ✗ ACME HTTP-01 validation will fail"
  echo "  Consider: Firewall rules, web server status, CDN configuration"
  exit 1
fi

echo ""
echo "=== A Record Configuration Valid for ACME ==="

Automated Monitoring Script

#!/bin/bash
# Monitor A record changes for ACME infrastructure

DOMAINS=("example.com" "www.example.com" "api.example.com")
STATE_FILE="/var/lib/dns-monitor/a-records.state"

for domain in "${DOMAINS[@]}"; do
  current_ip=$(dig +short "$domain" @8.8.8.8 | head -n1)
  previous_ip=$(grep "^$domain " "$STATE_FILE" 2>/dev/null | awk '{print $2}')

  if [ "$current_ip" != "$previous_ip" ]; then
    echo "ALERT: A record changed for $domain"
    echo "  Previous: $previous_ip"
    echo "  Current: $current_ip"

    # Send alert
    echo "DNS A record changed: $domain ($previous_ip → $current_ip)" | \
      mail -s "DNS Change Alert" [email protected]

    # Update state file
    sed -i "/^$domain /d" "$STATE_FILE"
    echo "$domain $current_ip" >> "$STATE_FILE"
  fi
done

5. Geographic Distribution for Global ACME Operations

Pattern: Regional subdomains for latency optimization

# Global DNS configuration for multi-region ACME
# Main domain
example.com.            300   IN   A   203.0.113.10  # US East (primary)
www.example.com.        300   IN   A   203.0.113.10

# Regional API endpoints
us-east.api.example.com. 300  IN   A   203.0.113.30  # AWS us-east-1
us-west.api.example.com. 300  IN   A   198.51.100.10 # AWS us-west-2
eu-west.api.example.com. 300  IN   A   192.0.2.10    # AWS eu-west-1
ap-south.api.example.com.300  IN   A   192.0.2.20    # AWS ap-south-1

# Each region runs its own Certbot instance
# Certificates issued independently per region
# Reduces cross-region latency for HTTP-01 validation

Terraform Multi-Region Implementation:

# Regional A record module
variable "regions" {
  type = map(object({
    subdomain = string
    ip_address = string
  }))
  default = {
    us-east = {
      subdomain = "us-east.api"
      ip_address = "203.0.113.30"
    }
    eu-west = {
      subdomain = "eu-west.api"
      ip_address = "192.0.2.10"
    }
    ap-south = {
      subdomain = "ap-south.api"
      ip_address = "192.0.2.20"
    }
  }
}

resource "cloudflare_record" "regional" {
  for_each = var.regions

  zone_id = var.zone_id
  name    = each.value.subdomain
  value   = each.value.ip_address
  type    = "A"
  ttl     = 300
}

output "regional_dns" {
  value = {
    for k, v in cloudflare_record.regional : k => {
      fqdn = v.hostname
      ip   = v.value
    }
  }
}

Common Pitfalls

1. Incomplete Subdomain Coverage for Multi-SAN Certificates

Problem: Creating A record only for apex domain, missing subdomains included in certificate

# Certificate request includes 3 domains:
certbot certonly -d example.com -d www.example.com -d blog.example.com

# But DNS only has:
example.com        A    203.0.113.10  ✓
www.example.com    A    203.0.113.10  ✓
blog.example.com   (missing)          ✗

# Result: HTTP-01 validation fails for blog.example.com

Solution: Create A records for ALL domains in certificate

example.com        300   IN   A   203.0.113.10
www.example.com    300   IN   A   203.0.113.10
blog.example.com   300   IN   A   203.0.113.10

2. Inconsistent TTL Values Causing Propagation Issues

Problem: Mixed TTL values cause unpredictable caching behavior

# WRONG - Inconsistent TTLs
example.com        3600   IN   A   203.0.113.10  # 1 hour
www.example.com    86400  IN   A   203.0.113.10  # 24 hours

# During IP migration:
# - example.com propagates in 1 hour
# - www.example.com takes 24 hours
# - Certificate validation inconsistent during migration window

Solution: Consistent TTL across related records

# CORRECT - Uniform TTL strategy
example.com        300   IN   A   203.0.113.10
www.example.com    300   IN   A   203.0.113.10
api.example.com    300   IN   A   203.0.113.20

# All use TTL 300 for consistent caching behavior

TTL Strategy for Migrations:

# Phase 1: Reduce TTL (24 hours before migration)
example.com        60    IN   A   203.0.113.10  # Old IP, short TTL

# Phase 2: Wait for old TTL to expire (24-48 hours)

# Phase 3: Update IP (migration day)
example.com        60    IN   A   198.51.100.10  # New IP, short TTL

# Phase 4: Stabilization period (1 week)
example.com        60    IN   A   198.51.100.10  # Keep short TTL

# Phase 5: Increase TTL after stable
example.com        1800  IN   A   198.51.100.10  # Increase to 30 minutes

3. Public Suffix List Complications with Dynamic DNS

Problem: Dynamic DNS providers (myasustor.com, duckdns.org) are on Public Suffix List

# Dynamic DNS hostname: mynas.myasustor.com
# Problem: Cannot issue certificate for *.myasustor.com
# Reason: myasustor.com is on Public Suffix List

# Certificate authorities treat mynas.myasustor.com as a "public suffix"
# Cannot issue wildcard *.myasustor.com

Solutions:

Option 1: Use custom domain

# Instead of: mynas.myasustor.com
# Use: nas.yourdomain.com (CNAME to mynas.myasustor.com)

nas.yourdomain.com    300   IN   CNAME   mynas.myasustor.com.

# Now you control yourdomain.com and can issue certificates

Option 2: Use DNS-01 challenge

# DNS-01 allows validation even for dynamic DNS
certbot certonly --manual --preferred-challenges dns \
  -d mynas.myasustor.com

Option 3: DuckDNS integration

# DuckDNS provides Let's Encrypt integration
# Update DuckDNS with your server IP
curl "https://www.duckdns.org/update?domains=yourdomain&token=YOUR_TOKEN&ip=203.0.113.10"

# Then use certbot with HTTP-01
certbot certonly --standalone -d yourdomain.duckdns.org

4. Split-Brain Infrastructure Without Intent

Problem: Apex and www pointing to different servers unintentionally

# WRONG - Unintentional split
example.com        300   IN   A   old_server_ip      # Forgotten old config
www.example.com    300   IN   A   new_server_ip      # Recent update

# Users see different content depending on whether they use apex or www
# Certificate validation may succeed on one but fail on the other

Symptoms:

$ curl http://example.com
# Returns old server content

$ curl http://www.example.com  
# Returns new server content

# Certificate on new server, ACME validation fails for apex

Solution: Audit and align A records

# CORRECT - Consistent IP mapping
example.com        300   IN   A   203.0.113.10
www.example.com    300   IN   A   203.0.113.10

# Verification script
apex_ip=$(dig +short example.com)
www_ip=$(dig +short www.example.com)

if [ "$apex_ip" != "$www_ip" ]; then
  echo "WARNING: Split-brain DNS detected"
  echo "Apex: $apex_ip"
  echo "WWW: $www_ip"
fi

Best Practices

1. TTL Strategy by Environment and Use Case

Production (Stable Services)

# Higher TTL reduces DNS query load, improves global performance
example.com        1800   IN   A   203.0.113.10  # 30 minutes
www.example.com    1800   IN   A   203.0.113.10
api.example.com    1800   IN   A   203.0.113.20

# Benefit: Reduced DNS query costs, faster resolution
# Trade-off: Slower propagation if IP changes needed

Migration/Maintenance Window

# Lower TTL enables faster infrastructure changes
example.com        300    IN   A   203.0.113.10  # 5 minutes
www.example.com    300    IN   A   203.0.113.10

# Benefit: Changes propagate quickly (5-15 minutes)
# Use case: Server migrations, failover scenarios

Development/Testing

# Very low TTL for rapid iteration
dev.example.com    60     IN   A   203.0.113.50  # 1 minute
staging.example.com 60    IN   A   203.0.113.51

# Benefit: Instant propagation for testing
# Trade-off: Higher DNS query load

ACME Certificate Operations

# Moderate TTL during certificate issuance/renewal
example.com        300    IN   A   203.0.113.10  # 5 minutes

# Allows quick DNS adjustments if HTTP-01 validation issues discovered
# After certificate stable, can increase to 1800-3600

2. Record Consistency Validation

Automated Consistency Check

#!/bin/bash
# Check A record consistency across apex and subdomains

DOMAIN="example.com"

apex_ip=$(dig +short "$DOMAIN" @8.8.8.8)
www_ip=$(dig +short "www.$DOMAIN" @8.8.8.8)

if [ "$apex_ip" == "$www_ip" ]; then
  echo "✓ A records consistent: $apex_ip"
else
  echo "✗ A record mismatch detected"
  echo "  Apex: $apex_ip"
  echo "  WWW: $www_ip"
  echo "  This may cause ACME validation issues"
  exit 1
fi

Multi-Domain Consistency Audit

import dns.resolver

def audit_dns_consistency(domains):
    """Verify all related domains point to same IP"""
    ips = {}

    for domain in domains:
        try:
            answers = dns.resolver.resolve(domain, 'A')
            ips[domain] = str(answers[0])
        except Exception as e:
            ips[domain] = f"ERROR: {e}"

    # Check consistency
    unique_ips = set([ip for ip in ips.values() if not ip.startswith("ERROR")])

    if len(unique_ips) > 1:
        print("WARNING: Inconsistent A records detected")
        for domain, ip in ips.items():
            print(f"  {domain} → {ip}")
        return False

    print(f"✓ All domains resolve to: {list(unique_ips)[0]}")
    return True

# Usage
domains = ["example.com", "www.example.com", "app.example.com"]
audit_dns_consistency(domains)

3. Health Monitoring for A Records

Prometheus DNS Monitoring

# blackbox_exporter configuration for A record monitoring
modules:
  dns_a_record:
    prober: dns
    dns:
      query_name: "example.com"
      query_type: "A"
      validate_answer_rrs:
        fail_if_not_matches_regexp:
        - "203\\.0\\.113\\.10"  # Expected IP pattern

Continuous DNS Monitoring

#!/bin/bash
# Continuous A record monitoring for ACME infrastructure

DOMAINS=("example.com" "www.example.com" "api.example.com")
EXPECTED_IPS=("203.0.113.10" "203.0.113.10" "203.0.113.20")
CHECK_INTERVAL=300  # 5 minutes

while true; do
  for i in "${!DOMAINS[@]}"; do
    domain="${DOMAINS[$i]}"
    expected="${EXPECTED_IPS[$i]}"

    current=$(dig +short "$domain" @8.8.8.8 | head -n1)

    if [ "$current" != "$expected" ]; then
      echo "ALERT: A record mismatch for $domain"
      echo "  Expected: $expected"
      echo "  Current: $current"

      # Send alert
      curl -X POST "https://monitoring.example.com/alert" \
        -d "domain=$domain&expected=$expected&current=$current"
    fi
  done

  sleep $CHECK_INTERVAL
done

4. Infrastructure as Code Best Practices

Version Control All DNS Changes

# Store in Git: terraform/dns/example.com.tf
# All changes go through PR review
# Deployment via CI/CD pipeline

terraform {
  backend "s3" {
    bucket = "company-terraform-state"
    key    = "dns/example.com"
    region = "us-east-1"
  }
}

# A records are infrastructure, not configuration
# Treat with same rigor as server provisioning

Prevent Manual DNS Changes

# Enforce IaC-only changes through DNS provider permissions
# Remove manual DNS edit access from ops team
# All changes must go through Terraform/Ansible

# AWS Route53 IAM policy (restrict to automation only)
{
  "Effect": "Allow",
  "Action": "route53:ChangeResourceRecordSets",
  "Resource": "arn:aws:route53:::hostedzone/*",
  "Condition": {
    "StringEquals": {
      "aws:PrincipalTag/automation": "terraform"
    }
  }
}

5. Geographic Distribution Patterns

GeoDNS for Regional Traffic Routing

# Route53 geolocation routing (not simple A records)
# North America traffic
example.com   300  IN  A  203.0.113.10 (geolocation: NA)

# Europe traffic
example.com   300  IN  A  198.51.100.10 (geolocation: EU)

# Asia Pacific traffic
example.com   300  IN  A  192.0.2.10 (geolocation: AP)

# Each region needs its own certificate with ACME automation

Global Load Balancer Pattern

# Single A record to global load balancer (Cloudflare, AWS Global Accelerator)
example.com        300   IN   A   104.16.x.x  # GLB anycast IP

# GLB routes to nearest region
# Certificate management centralized or per-region

---

Operational Checklist

Before implementing A records for ACME infrastructure:

• [ ] Define A record strategy (single server, multi-server, multi-region)
• [ ] Configure A records for apex domain (@)
• [ ] Configure A records for www subdomain
• [ ] Configure A records for all subdomains in certificate SAN list
• [ ] Ensure consistent TTL values across related records (300-1800s recommended)
• [ ] Verify A records resolve correctly from multiple public DNS resolvers
• [ ] Test HTTP connectivity to all resolved IP addresses
• [ ] Implement Infrastructure-as-Code for A record management (Terraform/Ansible)
• [ ] Configure version control for DNS changes
• [ ] Set up automated consistency checks (apex vs www)
• [ ] Implement A record change monitoring and alerting
• [ ] Document A record inventory and ownership
• [ ] Create DNS change management procedures
• [ ] Test A record failover procedures
• [ ] Configure backup DNS provider (secondary nameservers)
• [ ] Verify Public Suffix List status for dynamic DNS
• [ ] Document TTL reduction procedures for migrations
• [ ] Implement pre-migration A record validation
• [ ] Create runbook for A record emergency changes
• [ ] Set up automated DNS propagation verification

---

Related Documentation

ACME Operations: - Operating ACME Clients Overview - Section navigation - X.509 Certificate Verification - Certificate validation - Certbot Renewal Automation - Renewal patterns - DNS-01 Challenge Validation - DNS TXT records for validation - A Record Configuration - ACME-specific troubleshooting - DNS A Record Implementation (this page) - Infrastructure patterns - HTTP-01 Challenge Validation (coming) - HTTP-01 requiring proper A records

Infrastructure: - Certificate-as-Code - Infrastructure-as-Code patterns - Multi-Cloud PKI - Certificates across cloud providers - High Availability & Disaster Recovery - Failover patterns

Operations: - Certificate Lifecycle Management - Complete lifecycle - Monitoring and Alerting - Infrastructure monitoring

Troubleshooting: - Common Misconfigurations - Including DNS issues - Chain Validation Errors - Post-issuance problems

---

This comprehensive guide provides Infrastructure-as-Code patterns, multi-region strategies, and enterprise automation for A record implementation that supports scalable ACME certificate operations across diverse infrastructure environments.