Amazon Route 53: A Comprehensive Cheat Sheet

What is Amazon Route 53?

Amazon Route 53 is a highly available and scalable cloud Domain Name System (DNS) web service. It is designed to give developers and businesses an extremely reliable and cost-effective way to route end users to Internet applications. Route 53 effectively connects user requests to infrastructure running in AWS – such as Amazon EC2 instances, Elastic Load Balancing load balancers, or Amazon S3 buckets – and can also be used to route users to infrastructure outside of AWS. Its name is a reference to TCP/UDP port 53, where DNS server requests are addressed.

The service provides three main functions:

1. Domain Registration: You can purchase and manage domain names such as example.com.

2. DNS Routing: It translates human-readable domain names into the numeric IP addresses that computers use to connect to each other.

3. Health Checking: Route 53 can monitor the health of your application and its endpoints, automatically redirecting traffic to healthy endpoints.

Core Concepts

• Hosted Zone: A container for records that define how you want to route traffic for a domain (e.g., tutorialsdojo.com) and its subdomains. When you create a domain, Route 53 automatically creates a public hosted zone for it. You can also create private hosted zones for use within your Amazon VPCs.

• Record Set: Within a hosted zone, you create records (or record sets) to define how traffic for specific domain names (e.g., www.tutorialsdojo.com) should be directed.

• Record Types: Route 53 supports dozens of DNS record types, including common ones like A, AAAA, CNAME, MX, NS, and SOA. It also features a proprietary ALIAS record type.

Alias vs. CNAME Records: A Key Distinction

Choosing between an Alias record and a CNAME record is a common and important decision in Route 53.

| Feature | Alias Record | CNAME Record |

| ---------------------------- | -------------------------------------------------------------------------- | -------------------------------------------------------- |

| Zone Apex (Naked Domain) | Yes. Can be used for the zone apex (e.g., example.com). | No. Cannot be created at the zone apex. |

| Points To | Can only point to specific AWS resources (e.g., CloudFront, ELB, S3). | Can point to any DNS record hosted anywhere. |

| Billing | Queries to Alias records pointing to AWS resources are free. | Queries are charged at standard Route 53 rates. |

| Record Type in Response | Appears as the record type it's pointing to (e.g., A or AAAA). | Always appears as a CNAME record in DNS lookups. |

| How it Works | Route 53 resolves the alias to the resource's IP address directly. | Redirects the query to the target domain name. |

General Rule: Always prefer an Alias record when routing traffic to an AWS resource. Use a CNAME only when you need to point to a non-AWS resource or cannot use an Alias record for other reasons.

Route 53 Routing Policies Explained

Routing policies determine how Route 53 responds to DNS queries. Choosing the right policy is critical for designing your application's architecture.

Simple Routing

• Use Case: The most basic policy. Use for a single resource that performs a given function for your domain (e.g., one web server for example.com).

• How it Works: Route 53 returns the value(s) in the record (e.g., IP address). You cannot create multiple records with the same name and type. Health checks are not supported.

Failover Routing

• Use Case: Configure an active-passive failover. Use when you want to route traffic to a primary resource, but switch to a secondary (standby) resource if the primary becomes unhealthy.

• How it Works: You create a primary record and a secondary record. Route 53 monitors the health of the primary resource using health checks. If the primary fails its health check, Route 53 automatically begins responding to queries with the secondary record.

Weighted Routing

• Use Case: Route traffic to multiple resources in proportions that you specify (e.g., 90% to one server, 10% to another). Ideal for A/B testing, blue-green deployments, or load balancing across different server fleets.

• How it Works: You assign a "weight" (a number from 0 to 255) to each record. Route 53 sends traffic to a resource based on its weight as a proportion of the total weight for all records. You can set a weight to 0 to stop sending traffic to a resource.

Latency-Based Routing

• Use Case: Route users to the AWS region that provides the lowest possible latency. Ideal for global applications where performance is key.

• How it Works: You create records for your resources in multiple AWS Regions. When Route 53 receives a query, it determines which region will give the user the lowest round-trip time and returns the value from the record for that region.

Geolocation Routing

• Use Case: Route users based on their geographic location (continent, country, or state in the US). Ideal for serving localized content, meeting data sovereignty requirements, or restricting content distribution.

• How it Works: You create records that specify a geographic location. Route 53 identifies the location of the DNS query and responds with the record for the user's location. You should also create a default record for users who do not map to a specific location.

Geoproximity Routing

• Use Case: A more advanced form of location-based routing that routes traffic based on the physical distance between your users and your resources. You can also configure a "bias" to shift traffic towards or away from certain resources.

• How it Works: Requires using Route 53 Traffic Flow. It considers the user's location and the resource's location. You can apply a positive bias to expand the geographic area from which a resource gets traffic, or a negative bias to shrink it.

Multivalue Answer Routing

• Use Case: Similar to Simple Routing but allows you to return multiple values, such as IP addresses for several web servers. Route 53 will return up to eight healthy records chosen at random for each query.

• How it Works: This is a way to achieve a basic level of load balancing on the client-side. You can associate a health check with each record, and Route 53 will only return values for healthy resources.

Route 53 Health Checks

Route 53 can continuously monitor the health and performance of your application servers, and other resources.

• How they work: Route 53 sends automated requests over the internet to your endpoint to verify that it's reachable, available, and functional.

• Types of checks: You can monitor an endpoint (IP address or domain name), the status of other health checks (calculated health checks), or the state of a CloudWatch alarm.

• Integration: Health checks are the mechanism that enables DNS Failover and are also used with Multivalue Answer and Weighted routing policies to ensure traffic is not sent to unhealthy endpoints.