Scaling CoreDNS on AWS EKS: How Startups Can Avoid DNS Pitfalls at Scale
Imagine this scenario: you're scaling rapidly, traffic surges, and suddenly services start failing, not due to application bugs but DNS timeouts. Your AWS EKS infrastructure might scale effortlessly, but if your DNS setup isn't scaling with it, you're in trouble. Let's explore how to avoid these pitfalls.
CoreDNS is a flexible, Kubernetes-native DNS server responsible for resolving domain names within your EKS clusters. It maps services to IPs, enabling reliable internal communication and service discovery crucial for smooth operations.
Service reliability and latency
User experience
Infrastructure resilience during high traffic or growth
CoreDNS problems are subtle yet catastrophic. High latency, request throttling, or even minor misconfigurations can ripple across your entire stack, bringing down critical user-facing services. Ensuring CoreDNS scalability early on can save hours of troubleshooting later.
AWS’s built-in DNS resolver has hard limits:
Each network interface: 1,024 DNS packets/sec
Route 53 resolver endpoints: 10,000 queries/sec per endpoint
Exceed these, and queries fail silently or introduce latency. Monitor AWS CloudWatch Resolver metrics regularly.
Set your forward plugin carefully. Use caching wisely:
forward . /etc/resolv.conf {
max_concurrent 1000
policy round_robin
health_check 5s
}
cache {
success 20000 600
denial 20000 600
prefetch 5
}
Reduces AWS DNS throttling risk
Improves latency and service responsiveness
Use Kubernetes features like topologySpreadConstraints and Pod anti-affinity to ensure your DNS infrastructure doesn't become a single point of failure.
Misconception: DNS services don’t require special handling or scaling. Reality: DNS scales differently—issues are subtle, pervasive, and impactful.
Defaults are fine initially but can break at scale. Customized CoreDNS setups become necessary for stable scaling.
"Defaults break at scale. CoreDNS is no exception."
Reduced downtime and fewer mysterious network issues
Improved response times and overall user experience
Easier identification and resolution of infrastructure bottlenecks
Increased infrastructure robustness and reliability during scaling events
Monitor aggressively: Track CoreDNS metrics (coredns_forward_request_duration_seconds) and AWS resolver limits.
Use horizontal autoscaling: Match CoreDNS replica counts to cluster size and workload intensity.
Minimize external dependencies: Cache aggressively, reduce reliance on AWS’s VPC DNS, and use NodeLocal caches.
Scaling CoreDNS correctly isn’t just "nice-to-have"; it's essential for resilient, high-performing cloud infrastructure. Fast-growing startups often underestimate DNS impacts, paying a heavy price later. Proactively scaling your CoreDNS setup on AWS EKS ensures smooth infrastructure transitions and service reliability.