A Record Configuration Guide

TL;DR: A records map domain names to IPv4 addresses, forming the foundation of DNS-based routing that ACME HTTP-01 challenges depend on. Misconfigured A records are the leading cause of ACME HTTP-01 validation failures, causing certificates to fail issuance when the ACME CA cannot reach the correct server for challenge verification.

Overview: Why A Records Matter for ACME Operations

A records represent the most fundamental DNS record type—they tell the internet "when someone requests example.com, send them to IP address 192.0.2.1." While conceptually simple, A record configuration directly determines whether ACME HTTP-01 challenges succeed or fail. When Let's Encrypt validates your domain ownership, it queries DNS for your domain's A record, then connects to that IP address expecting to find the HTTP-01 challenge response.

The ACME dependency: HTTP-01 challenge validation follows this sequence: 1. Your ACME client requests a certificate for example.com 2. Let's Encrypt CA looks up example.com A record via DNS 3. CA connects to the IP address from step 2 4. CA requests http://example.com/.well-known/acme-challenge/<token> 5. Your server must respond with the correct validation token

If your A record points to the wrong server, Let's Encrypt connects to a different machine that doesn't have the validation token—certificate issuance fails. This fundamental misconfiguration accounts for approximately 40% of ACME HTTP-01 validation failures in production environments.

Why This Belongs in ACME Client Operations

While A records are DNS fundamentals, this guide focuses on ACME operational context—the specific A record configurations that enable or break certificate automation. Understanding DNS isn't enough; you need to understand how ACME CAs use A records during validation, how CDNs and load balancers complicate A record configuration, and how to debug A record issues that manifest as ACME failures.

Real-world ACME scenario: Your organization uses Cloudflare as a CDN proxy. You configure an A record pointing to Cloudflare's proxy IP (104.16.x.x). You run Certbot on your origin server (192.0.2.1). HTTP-01 validation fails because Let's Encrypt connects to Cloudflare, not your origin server. The validation token exists on your origin but is unreachable through the proxy.

When A Records Matter for ACME

A records are critical for: - HTTP-01 challenges: CA must reach your server via A record resolution - Root domain certificates: example.com (apex domain) requires A record (CNAME not allowed) - Multi-server environments: Ensuring validation happens on the certificate server - Load balancer configurations: Routing ACME validation to appropriate backends - Debugging certificate failures: 60% of HTTP-01 failures involve DNS misconfiguration

A records are NOT required for: - DNS-01 challenges: Validation uses TXT records, not A records (though A records may still exist) - Wildcard certificates: DNS-01 is required; A records irrelevant to validation - Internal certificates: Private ACME servers may not require public DNS resolution

This page is part of the Operating ACME Clients section:

Operating ACME Clients Overview - Section introduction and navigation
X.509 Certificate Verification - Certificate validation post-issuance
Certbot Renewal Automation - Renewal patterns assuming proper DNS
DNS-01 Challenge Validation - Alternative to HTTP-01 (bypasses A record issues)
A Record Configuration (this page) - DNS foundations for HTTP-01
HTTP-01 Challenge Validation (coming) - Detailed HTTP-01 implementation requiring proper A records

For broader DNS and infrastructure context: - Multi-Cloud PKI - DNS across cloud providers - Certificate Lifecycle Management - Lifecycle operations

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

For protocol understanding: - ACME Protocol - HTTP-01 challenge specification

Problem Statement

Organizations frequently encounter A record misconfigurations that result in ACME HTTP-01 validation failures:

Broken domain resolution: A records point to incorrect IP addresses, ACME CA cannot reach validation endpoint
SSL certificate validation failures: Let's Encrypt HTTP-01 challenge fails when A record points to CDN/proxy instead of origin server
Service disruptions: Multiple conflicting A records cause inconsistent DNS resolution, intermittent ACME failures
Root domain accessibility issues: Only www subdomain configured, root domain certificate requests fail
Traffic routing errors: A records point to load balancer VIP that doesn't route /.well-known/acme-challenge/ to certificate server
CDN proxy complications: A record points to CDN IP (Cloudflare, CloudFront) but ACME client runs on origin server

Common failure pattern:

ACME client log: "Timeout during connect (likely firewall problem)"
Reality: A record points to 104.16.132.229 (Cloudflare proxy)
Expected: A record should point to 192.0.2.1 (origin server with Certbot)

Architecture

A Record Structure (Standard DNS Format)

name    TTL    class    type    value
@       300    IN       A       192.0.2.1
www     300    IN       A       192.0.2.1
api     300    IN       A       192.0.2.2

Field Definitions: - name: Hostname (@ for root/apex domain, www for subdomain) - TTL: Time-to-live in seconds (how long DNS resolvers cache this record) - class: Always IN (Internet) for modern DNS - type: A for IPv4 addresses (vs AAAA for IPv6) - value: IPv4 address in dotted-decimal notation

Common A Record Patterns

Pattern 1: Root Domain Configuration

# Root/apex domain: example.com
@       300   IN    A    151.80.149.141

# Explanation:
# - @ symbol represents the apex/root domain
# - TTL 300 = 5 minutes cache time
# - Points to server at 151.80.149.141

Pattern 2: Complete Domain Setup (Root + WWW)

# Root domain: example.com
@       300   IN    A    192.0.2.1

# WWW subdomain: www.example.com  
www     300   IN    A    192.0.2.1

# Both point to same server (common pattern)

Pattern 3: Service-Specific Records

# Main website
@       300   IN    A    149.28.25.43
www     300   IN    A    149.28.25.43

# API on separate server
api     300   IN    A    149.28.25.44

# Streaming service on different infrastructure
stream  300   IN    A    103.43.75.123

Pattern 4: Multi-Server with Load Balancing

# Multiple A records for round-robin DNS load balancing
www     300   IN    A    192.0.2.1
www     300   IN    A    192.0.2.2
www     300   IN    A    192.0.2.3

# Warning: Complicates ACME HTTP-01 validation
# All servers must serve identical challenge responses

ACME HTTP-01 Validation Flow with A Records

┌─────────────┐         ┌─────────────┐         ┌─────────────┐
│   Client    │         │ Let's       │         │    DNS      │
│  (Certbot)  │         │  Encrypt    │         │  Resolver   │
└─────────────┘         └─────────────┘         └─────────────┘
       │                       │                        │
       │ 1. Request cert       │                        │
       │──────────────────────▶│                        │
       │                       │                        │
       │ 2. HTTP-01 challenge  │                        │
       │◀──────────────────────│                        │
       │                       │                        │
       │                       │ 3. DNS query           │
       │                       │───────────────────────▶│
       │                       │                        │
       │                       │ 4. Return A record IP  │
       │                       │◀───────────────────────│
       │                       │                        │
       │                       │ 5. HTTP GET to IP      │
       │                       │──────────────────┐     │
       │                       │                  │     │
       │                       │    /.well-known/ │     │
       │                       │    acme-challenge│     │
       │                       │                  │     │
┌──────▼──────┐                │ 6. Challenge     │     │
│   Server    │◀───────────────┴──response────────┘     │
│ (Must match │                                         │
│  A record)  │                                         │
└─────────────┘

Critical Point: The server IP in step 6 MUST match the A record returned in step 4, or validation fails.

Provider-Specific Syntax

Different DNS providers use different syntax for A record configuration:

Standard Zone File Format (BIND)

@       300   IN    A    151.80.149.141
www     300   IN    A    151.80.149.141

NameSilo

# Use blank hostname field for root domain
Hostname: [blank]
Type: A
Value: 149.28.25.43
TTL: 600

Cloudflare Dashboard

Type: A
Name: @
IPv4 address: 192.0.2.1
TTL: Auto
Proxy status: DNS only (Orange cloud OFF for ACME validation)

Route53 (AWS)

{
  "Name": "example.com.",
  "Type": "A",
  "TTL": 300,
  "ResourceRecords": [
    {"Value": "192.0.2.1"}
  ]
}

Implementation

Basic Configuration

Root Domain Only

# Create A record for root domain
# DNS provider interface or API:
Name: @
Type: A
Value: 151.80.149.141
TTL: 300

Root + WWW (Recommended)

# Root domain
Name: @
Type: A
Value: 192.0.2.1
TTL: 300

# WWW subdomain
Name: www
Type: A
Value: 192.0.2.1
TTL: 300

ACME-Specific Configurations

Single Server HTTP-01 Setup

# Server IP: 209.200.39.244
# Certbot installed on this server

# DNS Configuration:
@       300   IN    A    209.200.39.244
www     300   IN    A    209.200.39.244

# Verify resolution:
dig @8.8.8.8 example.com +short
# Should return: 209.200.39.244

Load Balancer Configuration

# Load balancer VIP: 192.0.2.100
# Backend servers: 192.0.2.1, 192.0.2.2, 192.0.2.3

# DNS Configuration (A record points to load balancer):
@       300   IN    A    192.0.2.100
www     300   IN    A    192.0.2.100

# Load balancer must route /.well-known/acme-challenge/ 
# to server with Certbot (e.g., 192.0.2.1)

# HAProxy configuration example:
acl is_acme_challenge path_beg /.well-known/acme-challenge
use_backend certbot_server if is_acme_challenge

CDN/Proxy Bypass for ACME

# Problem: A record points to CDN proxy IP
# Solution: Temporarily set DNS only mode during validation

# Cloudflare: Disable orange cloud (proxy) during certificate issuance
# Or use DNS-01 challenge instead of HTTP-01

Advanced Patterns

Split DNS for Internal/External

# External DNS (public internet):
@       300   IN    A    203.0.113.10  # Public IP

# Internal DNS (corporate network):
@       300   IN    A    10.0.0.50     # Internal IP

# For ACME: Ensure external DNS points to server that can respond to HTTP-01

Multi-Region Failover

# Primary region
@       300   IN    A    192.0.2.1

# During failover, update to backup region:
@       60    IN    A    198.51.100.1  # Reduced TTL for faster propagation

# Note: Certificate must be present on both servers

Verification Commands

Basic DNS Query

# Query Google DNS
dig @8.8.8.8 example.com A

# Query Cloudflare DNS
dig @1.1.1.1 example.com A

# Query OpenDNS
dig @208.67.222.222 example.com A

# Check multiple regions
dig @8.8.8.8 example.com A +short
dig @1.1.1.1 example.com A +short

ACME Validation Simulation

# Simulate what Let's Encrypt sees
DOMAIN="example.com"
IP=$(dig +short $DOMAIN @8.8.8.8 | head -n1)

echo "Domain $DOMAIN resolves to $IP"

# Test HTTP connectivity to that IP
curl -v http://$IP/.well-known/acme-challenge/test \
  -H "Host: $DOMAIN"

# Should be reachable for ACME validation to succeed

Comprehensive Validation Script

#!/bin/bash
DOMAIN="$1"

echo "=== A Record Validation for ACME ==="
echo "Domain: $DOMAIN"
echo ""

# Check A record from multiple DNS servers
echo "Checking A record resolution:"
for ns in 8.8.8.8 1.1.1.1 208.67.222.222; do
  ip=$(dig +short "$DOMAIN" @$ns | grep -E '^[0-9]+\.' | head -n1)
  echo "  $ns → $ip"
done

# Get primary IP
PRIMARY_IP=$(dig +short "$DOMAIN" @8.8.8.8 | grep -E '^[0-9]+\.' | head -n1)

if [ -z "$PRIMARY_IP" ]; then
  echo "ERROR: No A record found for $DOMAIN"
  exit 1
fi

echo ""
echo "Primary IP: $PRIMARY_IP"
echo ""

# Test HTTP connectivity
echo "Testing HTTP connectivity:"
if curl -s -o /dev/null -w "%{http_code}" --max-time 5 \
  "http://$PRIMARY_IP/.well-known/acme-challenge/test" \
  -H "Host: $DOMAIN" | grep -q "404\|200"; then
  echo "  ✓ HTTP server reachable on $PRIMARY_IP"
else
  echo "  ✗ Cannot reach HTTP server on $PRIMARY_IP"
  echo "  This will cause ACME HTTP-01 validation to fail"
fi

Common Pitfalls

1. Incomplete Root Domain Configuration

Problem: Creating only www subdomain A record, missing root domain

# WRONG - Missing root domain
www     300   IN    A    192.0.2.1

# Result: example.com doesn't resolve
# Impact: Cannot issue certificate for bare domain

Symptom:

$ dig example.com +short
# (no output - NXDOMAIN)

$ certbot certonly -d example.com
# Error: DNS query failed for example.com

Solution: Configure both root and www

# CORRECT
@       300   IN    A    192.0.2.1  
www     300   IN    A    192.0.2.1

# Verify both resolve:
$ dig example.com +short
192.0.2.1
$ dig www.example.com +short
192.0.2.1

2. Wrong IP Address Mapping

Problem: A record points to registrar's parking server or old IP

# WRONG - Points to registrar parking page
@       300   IN    A    195.20.52.215  # Registrar's server

# Impact: Let's Encrypt connects to registrar server,
# validation token doesn't exist there, validation fails

Symptoms:

$ curl http://example.com/.well-known/acme-challenge/test
# Returns registrar parking page HTML

$ certbot certonly --nginx -d example.com
# Error: The client lacks sufficient authorization

Solution: Update to actual server IP

# CORRECT - Points to your server where Certbot runs
@       300   IN    A    209.200.39.244

# Verify correct server responds:
$ curl -I http://209.200.39.244
# Should return headers from YOUR server

3. CDN/Proxy IP Configuration

Problem: A record points to CDN proxy IP while Certbot runs on origin

# WRONG for HTTP-01 validation
@       300   IN    A    104.16.132.229  # Cloudflare proxy IP

# Your Certbot server: 192.0.2.1
# Let's Encrypt connects to 104.16.132.229 (Cloudflare)
# Validation token is on 192.0.2.1 (unreachable)

Symptoms:

$ certbot certonly --nginx -d example.com
# Error: Fetching http://example.com/.well-known/acme-challenge/...
# Connection timed out

Solutions:

Option A: Use DNS-01 instead of HTTP-01

certbot certonly --dns-cloudflare \
  --dns-cloudflare-credentials ~/.secrets/cloudflare.ini \
  -d example.com

Option B: Temporarily disable CDN proxy

# Cloudflare: Turn off orange cloud (set to "DNS only")
# Issue certificate
# Re-enable orange cloud after cert issued

Option C: Configure CDN to proxy ACME challenges to origin

# Cloudflare Page Rule:
# URL: *example.com/.well-known/acme-challenge/*
# Setting: SSL = Flexible, Cache Level = Bypass

4. Multiple Conflicting A Records

Problem: Multiple A records with different IPs cause round-robin

# WRONG - Unintentional multiple A records
@       300   IN    A    192.0.2.1   # Old server
@       300   IN    A    192.0.2.2   # New server

# DNS returns both IPs in random order
# Let's Encrypt may connect to old server without validation token

Symptoms:

$ dig example.com +short
192.0.2.1
192.0.2.2

# Validation fails intermittently (50% of the time)

Solution: Single A record per hostname

# CORRECT - Only one A record
@       300   IN    A    192.0.2.2   # Current server only

# Delete old A record from DNS

5. TTL Too High During Migration

Problem: Long TTL delays DNS propagation during server changes

# WRONG - High TTL during server migration
@       86400 IN    A    192.0.2.1  # TTL = 24 hours

# Change server IP to 192.0.2.2
# Some DNS resolvers still cache old IP for 24 hours
# ACME validation fails on old IP

Solution: Reduce TTL before migration

# Step 1: Reduce TTL (24 hours before migration)
@       300   IN    A    192.0.2.1  # TTL = 5 minutes

# Step 2: Wait 24 hours for old TTL to expire

# Step 3: Update IP address
@       300   IN    A    192.0.2.2  # New IP, short TTL

# Step 4: After stable, increase TTL again
@       3600  IN    A    192.0.2.2  # TTL = 1 hour

6. Load Balancer Without ACME Routing

Problem: A record points to load balancer, but LB doesn't route ACME challenges correctly

# A record configuration:
@       300   IN    A    192.0.2.100  # Load balancer VIP

# Backend servers: 192.0.2.1, 192.0.2.2, 192.0.2.3
# Certbot runs on 192.0.2.1 only
# LB routes requests round-robin
# 66% of validation attempts fail (go to wrong backend)

Solution: Configure LB to route ACME challenges to specific backend

# Nginx load balancer configuration
upstream backend {
    server 192.0.2.1;  # Certbot server
    server 192.0.2.2;
    server 192.0.2.3;
}

upstream certbot_backend {
    server 192.0.2.1;  # Only Certbot server
}

server {
    listen 80;
    server_name example.com;

    # Route ACME challenges to Certbot server only
    location /.well-known/acme-challenge/ {
        proxy_pass http://certbot_backend;
    }

    # All other traffic load balanced
    location / {
        proxy_pass http://backend;
    }
}

7. Internal/External DNS Mismatch

Problem: Internal DNS has different A record than external DNS

# External DNS (public internet):
@       300   IN    A    203.0.113.10  # Public IP

# Internal DNS (corporate network):
@       300   IN    A    10.0.0.50     # Internal IP

# Certbot runs on internal network, tests against internal DNS
# Let's Encrypt validates against external DNS
# Potential mismatch if both servers don't serve identical content

Solution: Ensure both IPs serve ACME challenges

# Option 1: Run Certbot on publicly accessible server (203.0.113.10)

# Option 2: Configure internal server to handle ACME challenges
# and sync certificates to internal server

# Option 3: Use DNS-01 challenge (bypasses HTTP entirely)

Best Practices

1. Single A Record per Hostname (Unless Load Balancing)

Principle: One hostname = one IP address for predictable routing

# GOOD - Single A record per hostname
@       300   IN    A    203.0.113.10
www     300   IN    A    203.0.113.10
api     300   IN    A    203.0.113.11

# AVOID - Multiple A records unless intentionally load balancing
@       300   IN    A    203.0.113.10
@       300   IN    A    203.0.113.20  # Only if both servers identical

Exception: Round-robin DNS for load balancing

# Acceptable when all servers serve identical content
www     300   IN    A    192.0.2.1
www     300   IN    A    192.0.2.2
www     300   IN    A    192.0.2.3

# But ensure all servers can handle ACME challenges

2. Consistent IP Mapping Across Subdomains

Pattern: Related services on same server use same IP

# Production pattern - related services grouped
@       300   IN    A    203.0.113.10  # Main server
www     300   IN    A    203.0.113.10  # Same server
blog    300   IN    A    203.0.113.10  # Same server

api     300   IN    A    203.0.113.11  # API server
api-v2  300   IN    A    203.0.113.11  # Same API server

mail    300   IN    A    203.0.113.12  # Mail server
smtp    300   IN    A    203.0.113.12  # Same mail server

3. TTL Optimization for Different Scenarios

Production (Stable Services)

# Higher TTL reduces DNS query load, improves performance
@       3600  IN    A    203.0.113.10  # 1 hour
www     3600  IN    A    203.0.113.10

Migration/Maintenance Window

# Lower TTL enables faster changes
@       300   IN    A    203.0.113.10  # 5 minutes
www     300   IN    A    203.0.113.10

# After successful migration and stabilization, increase TTL

Development/Testing

# Very low TTL for rapid iteration
@       60    IN    A    203.0.113.10  # 1 minute
www     60    IN    A    203.0.113.10

ACME Certificate Issuance

# Moderate TTL during certificate operations
@       300   IN    A    203.0.113.10  # 5 minutes
# Allows quick DNS changes if validation issues discovered

4. Service Isolation and Purpose-Built IPs

Pattern: Separate IPs for different service types

# Web services cluster
@       300   IN    A    203.0.113.10
www     300   IN    A    203.0.113.10
app     300   IN    A    203.0.113.10

# API services cluster
api     300   IN    A    203.0.113.20
api-v1  300   IN    A    203.0.113.20
api-v2  300   IN    A    203.0.113.21

# Infrastructure services
vpn     300   IN    A    203.0.113.30
admin   300   IN    A    203.0.113.31

Benefit for ACME: Clear separation of certificate management responsibilities

5. SSL Certificate Validation Considerations

Critical Rule: A record must point to server where ACME client runs (for HTTP-01)

# Server running Certbot: 192.0.2.1

# CORRECT - A record points to Certbot server
@       300   IN    A    192.0.2.1

# Certificate issuance will succeed
certbot certonly --nginx -d example.com

Multi-Server Strategy:

# Option 1: Centralized certificate server
# One server issues certificates, distributes to others
cert-mgmt  300  IN  A  192.0.2.100  # Certificate management server

# Option 2: Direct issuance per server
web1       300  IN  A  192.0.2.1    # Each server issues own cert
web2       300  IN  A  192.0.2.2
web3       300  IN  A  192.0.2.3

6. Monitoring and Validation

Pre-Deployment Validation

#!/bin/bash
# Validate A record before ACME operations

DOMAIN="$1"

echo "Validating A record for $DOMAIN"

# Check A record exists
IP=$(dig +short "$DOMAIN" @8.8.8.8 | head -n1)
if [ -z "$IP" ]; then
  echo "ERROR: No A record found"
  exit 1
fi

echo "A record: $DOMAIN → $IP"

# Check server responds on that IP
if timeout 5 curl -sf "http://$IP" -H "Host: $DOMAIN" > /dev/null; then
  echo "✓ Server reachable at $IP"
else
  echo "✗ Server not reachable at $IP"
  echo "HTTP-01 validation will fail"
  exit 1
fi

echo "✓ A record configuration valid for ACME"

Continuous Monitoring

# Monitor A record changes
dig example.com @8.8.8.8 | grep "^example.com" | \
  mail -s "DNS A Record Check" [email protected]

# Alert on unexpected changes

Post-Change Verification

# After updating A record, verify propagation
for ns in 8.8.8.8 1.1.1.1 208.67.222.222 8.8.4.4; do
  echo -n "Checking $ns: "
  dig +short example.com @$ns
done

7. Documentation and Inventory

Maintain DNS Inventory

# DNS A Record Inventory

## Production Web Services
- example.com → 203.0.113.10 (primary-web-01)
- www.example.com → 203.0.113.10 (primary-web-01)
- app.example.com → 203.0.113.10 (primary-web-01)

## API Services  
- api.example.com → 203.0.113.20 (api-server-01)
- api-v2.example.com → 203.0.113.21 (api-server-02)

## Certificate Management
- Certbot installed on: primary-web-01 (203.0.113.10)
- Certificates managed: example.com, www.example.com, app.example.com
- Renewal: Automated via systemd timer

## Last Updated
- Date: 2026-01-24
- Changed by: ops-team
- Reason: New API server deployment

Change Management

# Document every A record change
Date: 2026-01-24
Domain: example.com
Old IP: 192.0.2.1
New IP: 203.0.113.10
Reason: Server migration
Impact: Requires certificate reissuance
Verified by: John Doe

8. Disaster Recovery Considerations

Backup DNS Configuration

# Export current DNS configuration
dig example.com ANY > dns-backup-example.com-$(date +%Y%m%d).txt

# Store A record configuration
cat > a-records-backup.txt << 'EOF'
@       300   IN    A    203.0.113.10
www     300   IN    A    203.0.113.10
api     300   IN    A    203.0.113.11
EOF

Failover Procedure

# 1. Reduce TTL (if not already low)
@       60    IN    A    203.0.113.10  # Primary

# 2. Update to backup IP during outage
@       60    IN    A    198.51.100.1  # Backup

# 3. Verify propagation
dig @8.8.8.8 example.com +short

# 4. Ensure certificates present on backup server
scp /etc/letsencrypt/live/example.com/* backup-server:/etc/ssl/

Operational Checklist

Before deploying ACME with HTTP-01 challenges:

[ ] Configure A record for root domain (@)
[ ] Configure A record for www subdomain
[ ] Verify A records resolve correctly from multiple DNS servers (8.8.8.8, 1.1.1.1, 208.67.222.222)
[ ] Ensure A record points to server where ACME client will run
[ ] Test HTTP connectivity to resolved IP address
[ ] Verify firewall allows HTTP (port 80) access from internet
[ ] Check for CDN/proxy interference (disable or configure bypass)
[ ] Confirm no conflicting A records exist
[ ] Set appropriate TTL (300-600 seconds recommended)
[ ] Document A record configuration in inventory
[ ] Test ACME challenge path accessibility: curl http://DOMAIN/.well-known/acme-challenge/test
[ ] Verify load balancer routes ACME challenges correctly (if applicable)
[ ] Check internal/external DNS consistency (if split DNS)
[ ] Establish monitoring for A record changes
[ ] Document rollback procedures for DNS changes
[ ] Create backup of DNS configuration

ACME Operations: - Operating ACME Clients Overview - Section navigation - X.509 Certificate Verification - Certificate validation - Certbot Renewal Automation - Renewal patterns - DNS-01 Challenge Validation - Alternative to HTTP-01 - HTTP-01 Challenge Validation (coming) - Detailed HTTP-01 requiring proper A records

Broader Operations: - Certificate Lifecycle Management - Complete lifecycle - Renewal Automation - Automation strategies

Implementation: - Multi-Cloud PKI - DNS across cloud providers - ACME Protocol Implementation - Building ACME servers

Troubleshooting: - Common Misconfigurations - Including DNS issues - Expired Certificate Outages - Incident response

Protocol: - ACME Protocol - HTTP-01 challenge specification - TLS Protocol - TLS and certificates

This comprehensive guide ensures proper A record configuration for successful ACME HTTP-01 challenge validation, preventing the most common cause of certificate issuance failures in production environments.

A Record Configuration Guide

Overview: Why A Records Matter for ACME Operations

Why This Belongs in ACME Client Operations

When A Records Matter for ACME

Related Documentation

Problem Statement

Architecture

A Record Structure (Standard DNS Format)

Common A Record Patterns

Pattern 1: Root Domain Configuration

Pattern 2: Complete Domain Setup (Root + WWW)

Pattern 3: Service-Specific Records

Pattern 4: Multi-Server with Load Balancing

ACME HTTP-01 Validation Flow with A Records

Provider-Specific Syntax

Standard Zone File Format (BIND)

NameSilo

Cloudflare Dashboard

Route53 (AWS)

Implementation

Basic Configuration

ACME-Specific Configurations

Single Server HTTP-01 Setup

Load Balancer Configuration

CDN/Proxy Bypass for ACME

Advanced Patterns

Split DNS for Internal/External

Multi-Region Failover

Verification Commands

Common Pitfalls

1. Incomplete Root Domain Configuration

2. Wrong IP Address Mapping

3. CDN/Proxy IP Configuration

4. Multiple Conflicting A Records

5. TTL Too High During Migration

6. Load Balancer Without ACME Routing

7. Internal/External DNS Mismatch

Best Practices

1. Single A Record per Hostname (Unless Load Balancing)

2. Consistent IP Mapping Across Subdomains

3. TTL Optimization for Different Scenarios

4. Service Isolation and Purpose-Built IPs

5. SSL Certificate Validation Considerations

6. Monitoring and Validation

7. Documentation and Inventory

8. Disaster Recovery Considerations

Operational Checklist

Related Documentation