When implementing your DNS configuration with separate TTL values for CNAME and A records, the caching behavior follows these precise rules:

# Example DNS Zone Configuration
# config.mydomain.com zone:
s2.config.mydomain.com.    IN A    10.0.0.2     ; TTL=60
mydomain.com.              IN CNAME s2.config.mydomain.com. ; TTL=3600

The resolution occurs in two distinct phases with independent caching:

1. CNAME Resolution: Client caches the CNAME mapping (mydomain.com → s2.config...) for 3600 seconds
2. A Record Resolution: Client caches the IP address (s2.config... → 10.0.0.2) for just 60 seconds

This means while the CNAME mapping remains cached for an hour, the underlying IP address will be refreshed every minute. Some important considerations:

# DNS query sequence example
1. Query: mydomain.com → Response: CNAME (TTL=3600)
2. Query: s2.config.mydomain.com → Response: A (TTL=60)
3. Subsequent queries within 60s use cached A record
4. After 60s: New A record query required even if CNAME cache remains valid

For dynamic environments, consider these improved approaches:

• Dynamic DNS: Implement DDNS clients on servers to auto-update records
• API-Enabled DNS: Use providers with programmatic record updates (AWS Route53, Cloudflare API)
• Service Discovery: Implement Consul or etcd for distributed configuration

For production environments, this Terraform configuration demonstrates a more maintainable approach:

# Terraform configuration for dynamic DNS
resource "aws_route53_record" "server" {
  zone_id = var.config_zone_id
  name    = "s2.config.mydomain.com"
  type    = "A"
  ttl     = 60
  records = [aws_instance.server.private_ip]
}

resource "aws_route53_record" "service" {
  zone_id = var.primary_zone_id  
  name    = "mydomain.com"
  type    = "CNAME"
  ttl     = 3600
  records = [aws_route53_record.server.fqdn]
}

When dealing with DNS configurations in complex environments, understanding the interaction between CNAME and A record TTLs is crucial. Here's what happens during resolution:

dig mydomain.com
;; ANSWER SECTION:
mydomain.com.        3600    IN    CNAME    s2.config.mydomain.com.
s2.config.mydomain.com. 60   IN    A        10.0.0.1

The critical point is that DNS resolvers cache each record independently based on its own TTL:

• The CNAME record (3600s TTL) will be cached separately
• The A record (60s TTL) will be cached separately

This means clients will:

1. Cache the CNAME mapping for 3600 seconds
2. Need to refresh the A record every 60 seconds

Your current setup creates a potential issue where:

# Resolver behavior example
1. First query (T=0):
   - mydomain.com → CNAME (3600s cache)
   - s2.config... → A (60s cache)

2. Subsequent query (T=61):
   - mydomain.com → still from cache
   - s2.config... → new lookup required

For dynamic environments, consider these solutions:

1. DNS Update Automation

# Example using nsupdate
nsupdate -k keyfile <

# Consul DNS query
dig @127.0.0.1 -p 8600 s2.service.consul

# Output would be direct A records with controlled TTLs

# Route 53 weighted records
s2.config.mydomain.com. 60 IN A 10.0.0.1
s2.config.mydomain.com. 60 IN A 10.0.0.2