Route 53 Routing Policies: Weighted, Latency, Failover, Geolocation, and Health Checks

Why routing policies exist

A DNS record normally returns a single answer. Route 53 routing policies allow the same record name to return different answers based on criteria: traffic weights, requester location, endpoint health, or network latency. This enables DNS-level traffic management without changing application code.

Weighted routing: gradual traffic shifting

Weighted routing distributes traffic proportionally. Multiple records with the same name but different weights:

# 90% to production, 10% to canary
resource "aws_route53_record" "api_prod" {
  zone_id        = aws_route53_zone.main.zone_id
  name           = "api.example.com"
  type           = "A"
  set_identifier = "production"
  ttl            = 60

  weighted_routing_policy {
    weight = 90
  }

  records = [aws_lb.production.dns_name]  # doesn't work with Alias — see note
}

resource "aws_route53_record" "api_canary" {
  zone_id        = aws_route53_zone.main.zone_id
  name           = "api.example.com"
  type           = "A"
  set_identifier = "canary"
  ttl            = 60

  weighted_routing_policy {
    weight = 10
  }

  records = [aws_lb.canary.dns_name]
}

Weight 0 sends no traffic to a record (effectively disables it without deleting it). If all records have weight 0, Route 53 returns all records equally.

For weighted routing to AWS resources (ALB, CloudFront), use Alias records with weighted policy:

resource "aws_route53_record" "api_prod" {
  zone_id        = aws_route53_zone.main.zone_id
  name           = "api.example.com"
  type           = "A"
  set_identifier = "production"

  weighted_routing_policy {
    weight = 90
  }

  alias {
    name                   = aws_lb.production.dns_name
    zone_id                = aws_lb.production.zone_id
    evaluate_target_health = true
  }
}

Latency routing: route to lowest-latency region

Route 53 routes each DNS query to the record in the AWS region with the lowest measured latency for the requester. Route 53 maintains a database of latency measurements between client locations and AWS regions:

resource "aws_route53_record" "api_us" {
  zone_id        = aws_route53_zone.main.zone_id
  name           = "api.example.com"
  type           = "A"
  set_identifier = "us-east-1"

  latency_routing_policy {
    region = "us-east-1"
  }

  alias {
    name                   = aws_lb.us_east.dns_name
    zone_id                = aws_lb.us_east.zone_id
    evaluate_target_health = true
  }
}

resource "aws_route53_record" "api_eu" {
  zone_id        = aws_route53_zone.main.zone_id
  name           = "api.example.com"
  type           = "A"
  set_identifier = "eu-west-1"

  latency_routing_policy {
    region = "eu-west-1"
  }

  alias {
    name                   = aws_lb.eu_west.dns_name
    zone_id                = aws_lb.eu_west.zone_id
    evaluate_target_health = true
  }
}

Latency routing is based on AWS's measured network latency data, not geographic proximity. A user in Germany might be routed to us-east-1 if Route 53's latency data shows lower latency there than eu-west-1. Combine with health checks so that if a region becomes unhealthy, traffic reroutes to the next-lowest-latency region.

Failover routing: active-passive DR

Failover routing has one primary and one secondary record. Traffic goes to primary when healthy; Route 53 returns secondary when primary's health check fails:

resource "aws_route53_health_check" "primary" {
  fqdn              = "api-primary.example.com"
  port              = 443
  type              = "HTTPS"
  resource_path     = "/health"
  failure_threshold = 3
  request_interval  = 30
}

resource "aws_route53_record" "api_primary" {
  zone_id        = aws_route53_zone.main.zone_id
  name           = "api.example.com"
  type           = "A"
  set_identifier = "primary"

  failover_routing_policy {
    type = "PRIMARY"
  }

  health_check_id = aws_route53_health_check.primary.id

  alias {
    name                   = aws_lb.primary.dns_name
    zone_id                = aws_lb.primary.zone_id
    evaluate_target_health = true
  }
}

resource "aws_route53_record" "api_secondary" {
  zone_id        = aws_route53_zone.main.zone_id
  name           = "api.example.com"
  type           = "A"
  set_identifier = "secondary"

  failover_routing_policy {
    type = "SECONDARY"
  }

  # Secondary doesn't need a health check — it's always returned when primary fails
  alias {
    name                   = aws_lb.dr.dns_name
    zone_id                = aws_lb.dr.zone_id
    evaluate_target_health = true
  }
}

Route 53 health checkers poll from multiple global locations. The endpoint is marked unhealthy when a configurable number of checkers agree it's down. With failure_threshold = 3 and request_interval = 30, health status changes in ~90 seconds.

# EU users go to EU stack
resource "aws_route53_record" "api_eu" {
  zone_id        = aws_route53_zone.main.zone_id
  name           = "api.example.com"
  type           = "A"
  set_identifier = "eu-users"

  geolocation_routing_policy {
    continent = "EU"
  }

  alias {
    name    = aws_lb.eu.dns_name
    zone_id = aws_lb.eu.zone_id
    evaluate_target_health = true
  }
}

# US users
resource "aws_route53_record" "api_us" {
  zone_id        = aws_route53_zone.main.zone_id
  name           = "api.example.com"
  type           = "A"
  set_identifier = "us-users"

  geolocation_routing_policy {
    country = "US"
  }

  alias {
    name    = aws_lb.us.dns_name
    zone_id = aws_lb.us.zone_id
    evaluate_target_health = true
  }
}

# Default: all other locations
resource "aws_route53_record" "api_default" {
  zone_id        = aws_route53_zone.main.zone_id
  name           = "api.example.com"
  type           = "A"
  set_identifier = "default"

  geolocation_routing_policy {
    country = "*"   # default — matches any location not covered by other records
  }

  alias { ... }
}