Networking for cloud-native apps: load balancing and DNS

Cloud-native apps run across many containers and nodes. A good network design uses load balancing to spread traffic and DNS to locate services. Together they protect performance and reliability.

Types of load balancing:

  • L4 load balancers operate at the transport layer, routing packets by IP and port. They are fast and simple.
  • L7 load balancers inspect HTTP and make routing decisions based on path, headers, or query strings.

External vs internal:

  • External load balancers sit at the edge and shield your services from direct exposure.
  • Internal load balancers handle east-west traffic inside a cluster or data center.

Common options:

  • Cloud providers offer managed load balancers, such as AWS ALB/NLB, Google Cloud Load Balancing, and Azure Front Door.
  • In Kubernetes, an Ingress controller plus a load balancer service is a typical pattern.
  • Service meshes like Istio or Linkerd add traffic control with sidecar proxies and can support gradual rollouts and retries.

DNS roles:

  • DNS maps names like api.example.com to a load balancer address, helping clients reach services.
  • Use A or AAAA records for stable endpoints; CNAMEs can point to a load balancer hostname.
  • Short TTLs help agility during deployments, while longer TTLs reduce DNS query volume.
  • For multi-region apps, global DNS with health checks can redirect clients to healthy regions.

Best practices:

  • keep health checks up to date and wire them to the load balancer and service probes.
  • use readiness probes to remove unhealthy pods quickly.
  • favor stable hostnames over hard coded IPs and plan for DNS-based failover.
  • for canary or blue/green releases, use traffic shifting at the load balancer or within the service mesh.
  • monitor latency, error rates, and DNS health to catch issues early.

Example: A microservice runs three replicas behind a load balancer. Clients reach api.example.com, which resolves to the LB. If a new version is deployed, traffic can be shifted gradually without touching client apps.

Conclusion: With solid load balancing and thoughtful DNS planning, cloud-native apps stay available and fast, even during failures.

Key Takeaways

  • Load balancing distributes requests and supports health checks.
  • DNS directs clients to healthy endpoints and can enable global failover.
  • Combine L4/L7 load balancers with DNS and, if needed, a service mesh for traffic control.