Route 53 splits DNS queries across multiple servers based on weights you assign.

Server 1: 11.22.33.44  Weight 70  -> 70% of users
Server 2: 55.66.77.88  Weight 20  -> 20% of users
Server 3: 99.11.22.33  Weight 10  -> 10% of users

Route 53 receives queries and returns different IPs based on the weight ratio.

How Weights Work

Weights do not need to sum to 100. Route 53 calculates the percentage automatically.

Weight 7, 2, 1  -> Total 10
  Server A: 7/10 = 70%
  Server B: 2/10 = 20%
  Server C: 1/10 = 10%

Same result as weights 70, 20, 10

Important Rules

Records Must Have Same Name and Type

Correct:
  myapp.com  A  11.22.33.44  Weight 70
  myapp.com  A  55.66.77.88  Weight 20
  myapp.com  A  99.11.22.33  Weight 10

Wrong:
  myapp.com      A  11.22.33.44  Weight 70
  www.myapp.com  A  55.66.77.88  Weight 20  (different name)
  myapp.com  CNAME  something    Weight 10  (different type)

Health Checks

If a server fails health check, Route 53 removes it and recalculates among healthy servers only.

Server 1: Weight 70  (Healthy)
Server 2: Weight 20  (DOWN - skipped)
Server 3: Weight 10  (Healthy)

New distribution:
  Server 1: 70/80 = 87.5%
  Server 3: 10/80 = 12.5%

Weight 0

Setting weight to 0 stops all traffic to that server without deleting the record.

Server 1: Weight 70  (gets traffic)
Server 2: Weight 0   (gets no traffic)
Server 3: Weight 30  (gets traffic)

If ALL records have weight 0, Route 53 returns all records equally like Simple Routing.

Use Cases

Load Balancing Across Regions

US-East:  Weight 50
EU-West:  Weight 30
AP-South: Weight 20