DNS and Load Balancing

• Azure-provided default name resolution works inside one VNet but can't cross VNets
• A public DNS zone resolves nothing until you delegate the domain at the registrar
• A record set groups all records of one name and one type
• A private DNS zone resolves only for VNets you attach with a virtual network link
• A VNet can autoregister into only one private DNS zone (not the other way round)
• Azure Load Balancer is Layer 4: it routes on the 5-tuple, never on URL or host
• Public vs internal load balancer is decided by the frontend IP type
• Every load balancer is four objects: frontend IP, backend pool, health probe, rule
• An inbound NAT rule forwards a frontend port to one specific backend VM
• Choose the Load Balancer SKU first: there is no in-place Basic-to-Standard upgrade
• Standard Load Balancer is the production answer; Basic was retired in 2025
• The default distribution is a 5-tuple hash and does NOT pin a client to a backend
• A Standard public Load Balancer gives backends NO default outbound internet access
• SNAT exhaustion comes from too many concurrent outbound flows, not inbound load
• A Standard Load Balancer is closed until an NSG allows the traffic
• An all-unhealthy backend pool serves nothing: suspect the health probe
• "Multiple regions" rules out Azure Load Balancer: it's a regional service
• Application Gateway is Layer 7 for HTTP routing within one region
• Traffic Manager routes at the DNS layer; Front Door routes at the HTTP edge
• Path-based rules route by URL path, with a default pool for non-matches
• Multi-site listeners route by host name for several sites on one gateway
• Load Balancer health probes come from 168.63.129.16 and must be allowed

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