Mapping a Domain to a Load Balancer: Alias Record vs CNAME

// ALB provides a DNS name, not a static IP
package com.bank.infrastructure;

public class AlbDnsExplainer {
    private static final String ALB_DNS = "my-alb-123456.ap-south-1.elb.amazonaws.com";

    public static void main(String[] args) {
        System.out.println("ALB DNS name: " + ALB_DNS);
        System.out.println("IPs behind this name CHANGE as AWS scales the ALB.");
        System.out.println("You must point your domain to this name, not to an IP.");
    }
}

// CNAME record concept
package com.bank.infrastructure;

public class CnameRecordExample {
    // CNAME: name -> another name (extra lookup needed)
    private static final String NAME = "www.bank.example.com";
    private static final String TARGET = "my-alb-123456.ap-south-1.elb.amazonaws.com";

    public static void main(String[] args) {
        System.out.println("CNAME: " + NAME + " -> " + TARGET);
        System.out.println("Client must resolve TARGET to get the IP (extra step)");
        System.out.println("Cannot be placed at zone apex (bank.example.com)");
    }
}

// Alias record concept
package com.bank.infrastructure;

public class AliasRecordExample {
    // Alias: name -> AWS resource's IPs directly (one step)
    private static final String NAME = "bank.example.com"; // apex OK!
    private static final String TARGET = "ALB:my-alb-123456";

    public static void main(String[] args) {
        System.out.println("Alias A record: " + NAME + " -> " + TARGET);
        System.out.println("Route 53 resolves internally to ALB's current IPs.");
        System.out.println("Client receives A records in ONE step.");
        System.out.println("Allowed at zone apex: YES");
        System.out.println("Query charge for AWS targets: FREE");
    }
}

// Comparison summary
package com.bank.infrastructure;

public class CnameVsAliasComparison {
    public static void main(String[] args) {
        System.out.println("CNAME:");
        System.out.println("  + Works with any DNS provider");
        System.out.println("  - Cannot sit at zone apex");
        System.out.println("  - Extra resolution step");
        System.out.println("  - Standard query charges");
        System.out.println();
        System.out.println("Alias:");
        System.out.println("  + Allowed at zone apex");
        System.out.println("  + One-step resolution");
        System.out.println("  + Free queries for AWS targets");
        System.out.println("  + Auto-tracks changing IPs");
        System.out.println("  - Only works inside Route 53");
    }
}

// Supported alias targets
package com.bank.infrastructure;

import java.util.List;

public class AliasTargets {
    public static final List<String> SUPPORTED = List.of(
        "Application Load Balancer (ALB)",
        "Network Load Balancer (NLB)",
        "CloudFront distribution",
        "S3 website endpoint",
        "API Gateway",
        "Elastic Beanstalk environment",
        "Another Route 53 record in the same zone"
    );

    public static void main(String[] args) {
        System.out.println("Supported alias targets:");
        SUPPORTED.forEach(t -> System.out.println("  - " + t));
    }
}

// When DNS is outside Route 53
package com.bank.infrastructure;

public class ExternalDnsLimitation {
    public static void main(String[] args) {
        System.out.println("DNS outside Route 53:");
        System.out.println("  - Cannot use alias records");
        System.out.println("  - Must use CNAME on a subdomain (www.bank.example.com)");
        System.out.println("  - Cannot map the naked domain to an ALB");
        System.out.println();
        System.out.println("Solution: migrate DNS to Route 53 for alias support.");
    }
}

// Common mistakes
package com.bank.infrastructure;

public class DnsMappingMistakes {
    public static void main(String[] args) {
        System.out.println("WRONG: A record with hardcoded ALB IP");
        System.out.println("  IPs change as AWS scales the ALB -> domain breaks");
        System.out.println();
        System.out.println("WRONG: CNAME at zone apex (bank.example.com)");
        System.out.println("  Violates DNS RFC -> unpredictable failures");
        System.out.println();
        System.out.println("CORRECT: Route 53 alias A record at apex");
        System.out.println("  Maps to ALB, tracks IPs, free queries, apex OK");
    }
}

package com.bank.aws;

public class AliasSeniorKnowledge {
    public static void main(String[] args) {
        // Cost: alias queries to AWS resources are free
        // CNAME queries are billed at standard Route 53 rates
        long dailyQueries = 5_000_000L;
        double cnameRate = 0.40 / 1_000_000; // per query
        double monthlyCost = dailyQueries * 30 * cnameRate;
        System.out.println("Monthly DNS cost with CNAME: $" + monthlyCost);
        System.out.println("Monthly DNS cost with Alias: $0.00");
    }
}

Monthly DNS cost with CNAME: $60.0
Monthly DNS cost with Alias: $0.00