What it Does

Client asks Route 53 for a domain. Route 53 returns one or multiple IPs. Client picks one and connects. No intelligence, no health checks.

Two Modes

Single Value

Route 53 returns one IP only.

Client: "Where is foo.example.com?"
Route 53: "11.22.33.44"
Client: Connects to 11.22.33.44

Multiple Value

Route 53 returns all IPs. Client randomly picks one.

Client: "Where is foo.example.com?"
Route 53: "11.22.33.44, 55.66.77.88, 99.11.22.33"
Client: Randomly picks one and connects

What "One Resource" Actually Means

You might have 3 physical servers but Route 53 sees them as one service — they all serve the same website.

Physical reality:
  Server 1 -> 11.22.33.44  (separate machine)
  Server 2 -> 55.66.77.88  (separate machine)
  Server 3 -> 99.11.22.33  (separate machine)

Route 53 perspective:
  All 3 serve the same website = ONE service, just replicated
  Route 53 returns all IPs and says "pick any, they all do the same job"

The Problem — No Health Checks

Server 1: 11.22.33.44  (Working)
Server 2: 55.66.77.88  (DOWN)
Server 3: 99.11.22.33  (Working)

Route 53 returns all 3 IPs anyway
Client randomly picks one
33% chance of landing on dead Server 2 -> Error
User must refresh and hope they get a working server

Route 53 does not know or care which servers are down. It just returns all IPs blindly.

Limitations