Load Balancing and DNS
What this domain tests
This domain tests L4/L7 load-balancing design - listeners, backend sets, health checks, policies - and DNS zone, resolver, and traffic-management choices.
Core rules
- OCI Load Balancer is regional and flexible: choose a minimum and maximum bandwidth (10 Mbps to 8 Gbps). It supports public or private, TCP/HTTP/HTTPS listeners, SSL termination, and session persistence.
- Backend sets define servers, ports, health-check policy, and load-balancing policy (weighted round robin, least connections, IP hash). A backend is used only when its health check passes.
- Network Load Balancer is Layer 4, non-proxy, preserves source IP, and suits extreme throughput or UDP.
- OCI DNS hosts public and private zones; the VCN resolver handles private names. Steering policies include failover, load balancer, geolocation, ASN, and IP-based; health checks drive failover.
Worked example
Publish app.example.com. Create a public load balancer in a regional public subnet, listener HTTPS 443 with a certificate, backend set HTTP 8080, health check GET /health expecting 200, and weighted round robin 70/30 across two backend sets. In DNS, create zone example.com, an A record for app pointing to the LB public IP (or a CNAME from www to app), and a failover steering policy with a secondary standby. Reasoning: terminate TLS at the LB, keep health checks on the app port and path, and let DNS failover handle regional loss.
Traps
- Health-check port/path mismatches mark healthy servers down.
- Session persistence must match the application (cookie vs source IP).
- Putting the LB in an AD-specific subnet when a regional subnet is required.
- Forgetting that private DNS zones must be associated with the VCN.
- Assuming DNS changes propagate instantly; respect TTLs.