AWS Route 53 & Routing Policy

Amazon Route 53

You can use Amazon Route 53 to register new domains, transfer existing domains, route traffic for your domains to your AWS and external resources, and monitor the health of your resources.

Amazon Route 53 (Route 53) is a scalable and highly available Domain Name System (DNS). It is part of Amazon.com's cloud computing platform, Amazon Web Services (AWS). The name is a reference to TCP or UDP port 53, where DNS server requests are addressed. ... Route 53's servers are distributed throughout the world.

DNS management

If you already have a domain name, such as example.com, Route 53 can tell the Domain Name System (DNS) where on the Internet to find web servers, mail servers, and other resources for your domain.
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Traffic management

Route 53 traffic flow provides a visual tool that you can use to create and update sophisticated routing policies to route end users to multiple endpoints for your application.
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Availability monitoring

Route 53 can monitor the health and performance of your application as well as your web servers and other resources. Route 53 can also redirect traffic to healthy resources.
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Domain registration

If you need a domain name, you can find an available name and register it by using Route 53. You can also make Route 53 the registrar for existing domains that you registered with other registrars.
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What Is Amazon Route 53?

You can use Amazon Route 53 to help you get a website or web application up and running. Amazon Route 53 performs three main functions:

• Register domain names – Your website needs a name, such as example.com. Amazon Route 53 lets you register a name for your website or web application, known as a domain name. For an overview, see How Domain Registration Works.
• Route internet traffic to the resources for your domain – When a user opens a web browser and enters your domain name in the address bar, Amazon Route 53 helps the Domain Name System (DNS) connect the browser with your website or web application. For an overview, see How Internet Traffic Is Routed to Your Website or Web Application.
• Check the health of your resources – Amazon Route 53 sends automated requests over the internet to a resource, such as a web server, to verify that it's reachable, available, and functional. You also can choose to receive notifications when a resource becomes unavailable and choose to route internet traffic away from unhealthy resources. For an overview, see How Amazon Route 53 Checks the Health of Your Resources.

You can use any combination of these functions. For example, you can use Amazon Route 53 both to register your domain name and to route internet traffic for the domain, or you can use Amazon Route 53 to route internet traffic for a domain that you registered with another domain registrar. If you choose to use Amazon Route 53 for all three functions, you register your domain name, then configure Amazon Route 53 to route internet traffic for your domain, and finally configure Amazon Route 53 to check the health of your resources.

Topics

• How Domain Registration Works
• How Internet Traffic Is Routed to Your Website or Web Application
• How Amazon Route 53 Checks the Health of Your Resources
• Amazon Route 53 Concepts
• How to Get Started with Amazon Route 53
• Related Services
• Accessing Amazon Route 53
• AWS Identity and Access Management
• Amazon Route 53 Pricing
• HIPAA Compliance

Choosing a Routing Policy

When you create a resource record set, you choose a routing policy, which determines how Amazon Route 53 responds to queries:

• Simple routing policy – Use for a single resource that performs a given function for your domain, for example, a web server that serves content for the example.com website.
• Failover routing policy – Use when you want to configure active-passive failover.
• Geolocation routing policy – Use when you want to route traffic based on the location of your users.
• Geoproximity routing policy – Use when you want to route traffic based on the location of your resources and, optionally, shift traffic from one resources in one location to resources in another.
• Latency routing policy – Use when you have resources in multiple locations and you want to route traffic to the resource that provides the best latency.
• Multivalue answer routing policy – Use when you want Amazon Route 53 to respond to DNS queries with up to eight healthy records selected at random.
• Weighted routing policy – Use to route traffic to multiple resources in proportions that you specify.

How Domain Registration Works

If you want to create a website or a web application, you start by registering the name of your website, known as a domain name. Your domain name is the name, such as example.com, that your users enter in a browser to display your website.

Here's an overview of how you register a domain name with Amazon Route 53:

1. You choose a domain name and confirm that it's available, meaning that no one else has registered the domain name that you want.
   If the domain name you want is already in use, you can try other names or try changing only the top-level domain, such as .com, to another top-level domain, such as .ninja or .hockey. For a list of the top-level domains that Amazon Route 53 supports, see Domains That You Can Register with Amazon Route 53.
2. You register the domain name with Amazon Route 53. When you register a domain, you provide names and contact information for the domain owner and other contacts.
   When you register a domain with Amazon Route 53, the service automatically makes itself the DNS service for the domain by doing the following:
   • Creates a hosted zone that has the same name as your domain.
   • Assigns a set of four name servers to the hosted zone. When someone uses a browser to access your website, such as www.example.com, these name servers tell the browser where to find your resources, such as a web server or an Amazon S3 bucket. (Amazon S3 is object storage for storing and retrieving any amount of data from anywhere on the web. A bucket is a container for objects that you store in S3.)
   • Gets the name servers from the hosted zone and adds them to the domain.
   For more information, see How Internet Traffic Is Routed to Your Website or Web Application.
3. At the end of the registration process, we send your information to the registrar for the domain. The domain registrar is either Amazon Registrar, Inc. or our registrar associate, Gandi. To find out who the registrar is for your domain, see Domains That You Can Register with Amazon Route 53.
4. The registrar sends your information to the registry for the domain. A registry is a company that sells domain registrations for one or more top-level domains, such as .com.
5. The registry stores the information about your domain in their own database and also stores some of the information in the public WHOIS database.

For more information about how to register a domain name, see Registering a New Domain.

If you already registered a domain name with another registrar, you can choose to transfer the domain registration to Amazon Route 53. This isn't required to use other Amazon Route 53 features. For more information, see Transferring Registration for a Domain to Amazon Route 53.

How Internet Traffic Is Routed to Your Website or Web Application

All computers on the internet, from your smart phone or laptop to the servers that serve content for massive retail websites, communicate with one another by using numbers. These numbers, known as IP addresses, are in one of the following formats:

• Internet Protocol version 4 (IPv4) format, such as 192.0.2.44
• Internet Protocol version 6 (IPv6) format, such as 2001:0db8:85a3:0000:0000:abcd:0001:2345

When you open a browser and go to a website, you don't have to remember and enter a long number like that. Instead, you can enter a domain name like example.com and still end up in the right place. A DNS service such as Amazon Route 53 helps to make that connection between domain names and IP addresses.

Topics

• How to Configure Amazon Route 53 to Route Internet Traffic for Your Domain
• How Amazon Route 53 Routes Traffic for Your Domain

How Amazon Route 53 Checks the Health of Your Resources

Amazon Route 53 health checks monitor the health of your resources such as web servers and email servers. You can optionally configure Amazon CloudWatch alarms for your health checks, so that you receive notification when a resource becomes unavailable.

Here's an overview of how health checking works if you want to be notified when a resource becomes unavailable:

1. You create a health check and specify values that define how you want the health check to work, such as the following:
   • The IP address or domain name of the endpoint, such as a web server, that you want Amazon Route 53 to monitor. (You can also monitor the status of other health checks, or the state of a CloudWatch alarm.)
   • The protocol that you want Amazon Route 53 to use to perform the check: HTTP, HTTPS, or TCP.
   • How often you want Amazon Route 53 to send a request to the endpoint. This is therequest interval.
   • How many consecutive times the endpoint must fail to respond to requests before Amazon Route 53 considers it unhealthy. This is the failure threshold.
   • Optionally, how you want to be notified when Amazon Route 53 detects that the endpoint is unhealthy. When you configure notification, Amazon Route 53 automatically sets a CloudWatch alarm. CloudWatch uses Amazon SNS to notify users that an endpoint is unhealthy.
2. Amazon Route 53 starts to send requests to the endpoint at the interval that you specified in the health check.
   If the endpoint responds to the requests, Amazon Route 53 considers the endpoint to be healthy and takes no action.
3. If the endpoint doesn't respond to a request, Amazon Route 53 starts to count the number of consecutive requests that the endpoint doesn't respond to:
   • If the count reaches the value that you specified for the failure threshold, Amazon Route 53 considers the endpoint unhealthy.
   • If the endpoint starts to respond again before the count reaches the failure threshold, Amazon Route 53 resets the count to 0, and CloudWatch doesn't contact you.
4. If Amazon Route 53 considers the endpoint unhealthy and if you configured notification for the health check, Amazon Route 53 notifies CloudWatch.
   If you didn't configure notification, you can still see the status of your Amazon Route 53 health checks in the Amazon Route 53 console. For more information, see Monitoring Health Check Status and Getting Notifications.
5. If you configured notification for the health check, CloudWatch triggers an alarm and uses Amazon SNS to send notification to the specified recipients.

In addition to checking the health of a specified endpoint, you can configure a health check to check the health of one or more other health checks so that you can be notified when a specified number of resources, such as two web servers out of five, are unavailable. You can also configure a health check to check the status of a CloudWatch alarm so that you can be notified on the basis of a broad range of criteria, not just whether a resource is responding to requests.

If you have multiple resources that perform the same function, for example, web servers or database servers, and you want Amazon Route 53 to route traffic only to the resources that are healthy, you can configure DNS failover by associating a health check with each resource record set for that resource. If a health check determines that the underlying resource is unhealthy, Amazon Route 53 routes traffic away from the associated resource record set.

For more information about using Amazon Route 53 to monitor the health of your resources, see Creating Amazon Route 53 Health Checks and Configuring DNS Failover.

Amazon Route 53 Concepts

Here's an overview of the concepts that are discussed throughout the Amazon Route 53 Developer Guide.

Topics

• Domain Registration Concepts
• Domain Name System (DNS) Concepts
• Health Checking Concepts

Domain Registration Concepts

Here's an overview of the concepts that are related to domain registration.

• domain name
• domain registrar
• domain registry
• domain reseller
• top-level domain (TLD)

domain name

The name, such as example.com, that a user types in the address bar of a web browser to access a website or a web application. To make your website or web application available on the internet, you start by registering a domain name. For more information, see How Domain Registration Works.

domain registrar

A company that is accredited by ICANN (Internet Corporation for Assigned Names and Numbers) to process domain registrations for specific top-level domains (TLDs). For example, Amazon Registrar, Inc. is a domain registrar for .com, .net, and .org domains. Our registrar associate, Gandi, is a domain registrar for hundreds of TLDs, such as .apartments, .boutique, and .camera. For more information, see Domains That You Can Register with Amazon Route 53.

domain registry

A company that owns the right to sell domains that have a specific top-level domain. For example, VeriSign is the registry that owns the right to sell domains that have a .com TLD. A domain registry defines the rules for registering a domain, such as residency requirements for a geographic TLD. A domain registry also maintains the authoritative database for all of the domain names that have the same TLD. The registry's database contains information such as contact information and the name servers for each domain.

domain reseller

A company that sells domain names for registrars such as Amazon Registrar. Amazon Route 53 is a domain reseller for Amazon Registrar and for our registrar associate, Gandi.

top-level domain (TLD)

The last part of a domain name, such as .com, .org, or .ninja. There are two types of top-level domains:

generic top-level domains

These TLDs typically give users an idea of what they'll find on the website. For example, domain names that have a TLD of .bike often are associated with websites for motorcycle or bicycle businesses or organizations. With a few exceptions, you can use any generic TLD you want, so a bicycle club could use the .hockey TLD for their domain name.

geographic top-level domains

These TLDs are associated with geographic areas such as countries or cities. Some registries for geographic TLDs have residency requirements, while others, such as.io, allow or even encourage use as a generic TLD.

For a list of the TLDs that you can use when you register a domain name with Amazon Route 53, see Domains That You Can Register with Amazon Route 53.

Domain Name System (DNS) Concepts

Here's an overview of the concepts that are related to the Domain Name System (DNS).

• alias resource record set
• authoritative name server
• DNS query
• DNS resolver
• Domain Name System (DNS)
• hosted zone
• IP address
• name servers
• private DNS
• recursive name server
• resource record set (DNS record)
• reusable delegation set
• subdomain
• time to live (TTL)

alias resource record set

A type of resource record set that you can create with Amazon Route 53 to route traffic to AWS resources such as Amazon CloudFront distributions and Amazon S3 buckets. For more information, see Choosing Between Alias and Non-Alias Resource Record Sets.

authoritative name server

A name server that has definitive information about one part of the Domain Name System (DNS) and that responds to requests from a DNS resolver by returning the applicable information. For example, an authoritative name server for the .com top-level domain (TLD) knows the names of the name servers for every registered .com domain. When a .com authoritative name server receives a request from a DNS resolver for example.com, it responds with the names of the name servers for the DNS service for the example.com domain.

Amazon Route 53 name servers are the authoritative name servers for every domain that uses Amazon Route 53 as the DNS service. The name servers know how you want to route traffic for your domain and subdomains based on the resource record sets that you created in the hosted zone for the domain. (Amazon Route 53 name servers store the hosted zones for the domains that use Amazon Route 53 as the DNS service.)

For example, if an Amazon Route 53 name server receives a request for www.example.com, it finds that record and returns the IP address, such as 192.0.2.33, that is specified in the record.

DNS query

Usually a request that is submitted by a device, such as a computer or a smart phone, to the Domain Name System (DNS) for a resource that is associated with a domain name. The most common example of a DNS query is when a user opens a browser and types the domain name in the address bar. The response to a DNS query typically is the IP address that is associated with a resource such as a web server. The device that initiated the request uses the IP address to communicate with the resource. For example, a browser can use the IP address to get a web page from a web server.

DNS resolver

A DNS server, often managed by an internet service provider (ISP), that acts as an intermediary between user requests and DNS name servers. When you open a browser and type a domain name in the address bar, your query goes first to a DNS resolver. The resolver communicates with DNS name servers to get the IP address for the corresponding resource, such as a web server. A DNS resolver is also known as a recursive name server because it sends requests to a sequence of authoritative DNS name servers until it gets the response (typically an IP address) that it returns to a user's device, for example, a web browser on a laptop computer.

Domain Name System (DNS)

A worldwide network of servers that help computers, smart phones, tablets, and other IP-enabled devices to communicate with one another. The Domain Name System translates easily understood names such as example.com into the numbers, known as IP addresses, that allow computers to find each other on the internet.

See also IP address.

hosted zone

A container for resource record sets, which include information about how you want to route traffic for a domain (such as example.com) and all of its subdomains (such as www.example.com, retail.example.com, and seattle.accounting.example.com). A hosted zone has the same name as the corresponding domain.

For example, the hosted zone for example.com might include a resource record set that has information about routing traffic for www.example.com to a web server that has the IP address 192.0.2.243, and a resource record set that has information about routing email for example.com to two email servers, mail1.example.com and mail2.example.com. Each email server also requires its own resource record set.

See also resource record set (DNS record).

IP address

A number that is assigned to a device on the internet—such as a laptop, a smart phone, or a web server—that allows the device to communicate with other devices on the internet. IP addresses are in one of the following formats:

• Internet Protocol version 4 (IPv4) format, such as 192.0.2.44
• Internet Protocal version 6 (IPv6) format, such as 2001:0db8:85a3:0000:0000:abcd:0001:2345

Amazon Route 53 supports both IPv4 and IPv6 addresses for the following purposes:

• You can create resource record sets that have a type of A, for IPv4 addresses, or a type of AAAA, for IPv6 addresses.
• You can create health checks that send requests either to IPv4 or to IPv6 addresses.
• If a DNS resolver is on an IPv6 network, it can use either IPv4 or IPv6 to submit requests to Amazon Route 53.

name servers

Servers in the Domain Name System (DNS) that help to translate domain names into the IP addresses that computers use to communicate with one another. Name servers are either recursive name servers (also known as DNS resolver) or authoritative name servers.

For an overview of how DNS routes traffic to your resources, including the role of Amazon Route 53 in the process, see How Amazon Route 53 Routes Traffic for Your Domain.

private DNS

A local version of the Domain Name System (DNS) that lets you route traffic for a domain and its subdomains to Amazon EC2 instances within one or more Amazon virtual private clouds (VPCs). For more information, see Working with Private Hosted Zones.

recursive name server

See DNS resolver.

resource record set (DNS record)

An object in a hosted zone that you use to define how you want to route traffic for the domain or a subdomain. For example, you might create resource record sets for example.com and www.example.com that route traffic to a web server that has an IP address of 192.0.2.234.

For more information about resource record sets, including information about functionality that is provided by Amazon Route 53–specific resource record sets, see Configuring Amazon Route 53 as Your DNS Service.

reusable delegation set

A set of four authoritative name servers that you can use with more than one hosted zone. By default, Amazon Route 53 assigns a random selection of name servers to each new hosted zone. To make it easier to migrate DNS service to Amazon Route 53 for a large number of domains, you can create a reusable delegation set and then associate the reusable delegation set with new hosted zones. (You can't change the name servers that are associated with an existing hosted zone.)

You create a reusable delegation set and associate it with a hosted zone programmatically; using the Amazon Route 53 console isn't supported. For more information, see CreateHostedZone and CreateReusableDelegationSet in the Amazon Route 53 API Reference. The same feature is also available in the AWS SDKs, the AWS Command Line Interface, and AWS Tools for Windows PowerShell.

subdomain

A domain name that has one or more labels prepended to the registered domain name. For example, if you register the domain name example.com, then www.example.com is a subdomain. If you create the hosted zone accounting.example.com for the example.com domain, then seattle.accounting.example.com is a subdomain.

To route traffic for a subdomain, create a resource record set that has the name that you want, such as www.example.com, and specify the applicable values, such as the IP address of a web server.

time to live (TTL)

The amount of time, in seconds, that you want a DNS resolver to cache (store) the values for a resource record set before submitting another request to Amazon Route 53 to get the current values for that resource record set. If the DNS resolver receives another request for the same domain before the TTL expires, the resolver returns the cached value.

A longer TTL reduces your Amazon Route 53 charges, which are based in part on the number of DNS queries that Amazon Route 53 responds to. A shorter TTL reduces the amount of time that DNS resolvers route traffic to older resources after you change the values in a resource record set, for example, by changing the IP address for the web server for www.example.com.

Health Checking Concepts

Here's an overview of the concepts that are related to Amazon Route 53 health checking.

• DNS failover
• endpoint
• health check

DNS failover

A method for routing traffic away from unhealthy resources and to healthy resources. When you have more than one resource performing the same function—for example, more than one web server or mail server—you can configure Amazon Route 53 health checks to check the health of your resources and configure resource record sets in your hosted zone to route traffic only to healthy resources.

For more information, see Configuring DNS Failover.

endpoint

The resource, such as a web server or an email server, that you configure a health check to monitor the health of. You can specify an endpoint by IPv4 address (192.0.2.243), by IPv6 address (2001:0db8:85a3:0000:0000:abcd:0001:2345), or by domain name (example.com).

Note

You can also create health checks that monitor the status of other health checks or that monitor the alarm state of a CloudWatch alarm.

health check

An Amazon Route 53 component that lets you do the following:

• Monitor whether a specified endpoint, such as a web server, is healthy
• Optionally, get notified when an endpoint becomes unhealthy
• Optionally, configure DNS failover, which allows you to reroute internet traffic from an unhealthy resource to a healthy resource

For more information about how to create and use health checks, see Creating Amazon Route 53 Health Checks and Configuring DNS Failover.

How to Get Started with Amazon Route 53

For information about getting started with Amazon Route 53, see the following topics in this guide:

• Setting Up Amazon Route 53, which explains how to sign up for AWS, how to secure access to your AWS account, and how to set up programmatic access to Amazon Route 53
• Getting Started with Amazon Route 53, which describes how to register a domain name, how to create an Amazon S3 bucket and configure it to host a static website, and how to route internet traffic to the website

Accessing Amazon Route 53

You can access Amazon Route 53 in the following ways:

• AWS Management Console – The procedures throughout this guide explain how to use the AWS Management Console to perform tasks.
• AWS SDKs – If you're using a programming language that AWS provides an SDK for, you can use an SDK to access Amazon Route 53. SDKs simplify authentication, integrate easily with your development environment, and provide easy access to Amazon Route 53 commands. For more information, see Tools for Amazon Web Services.
• Amazon Route 53 API – If you're using a programming language that an SDK isn't available for, see the Amazon Route 53 API Reference for information about API actions and about how to make API requests.
• AWS Command Line Interface – For more information, see Getting Set Up with the AWS Command Line Interface in the AWS Command Line Interface User Guide.
• AWS Tools for Windows PowerShell – For more information, see Setting up the AWS Tools for Windows PowerShell in the AWS Tools for Windows PowerShell User Guide.

Amazon Route 53 Pricing

As with other AWS products, there are no contracts or minimum commitments for using Amazon Route 53—you pay only for the hosted zones that you configure and the number of DNS queries that Amazon Route 53 answers. For more information, see Amazon Route 53 Pricing.

Choosing a Routing Policy

When you create a resource record set, you choose a routing policy, which determines how Amazon Route 53 responds to queries:

• Simple routing policy – Use for a single resource that performs a given function for your domain, for example, a web server that serves content for the example.com website.
• Failover routing policy – Use when you want to configure active-passive failover.
• Geolocation routing policy – Use when you want to route traffic based on the location of your users.
• Geoproximity routing policy – Use when you want to route traffic based on the location of your resources and, optionally, shift traffic from one resources in one location to resources in another.
• Latency routing policy – Use when you have resources in multiple locations and you want to route traffic to the resource that provides the best latency.
• Multivalue answer routing policy – Use when you want Amazon Route 53 to respond to DNS queries with up to eight healthy records selected at random.
• Weighted routing policy – Use to route traffic to multiple resources in proportions that you specify.

Topics

• Failover Routing
• Geolocation Routing
• Geoproximity Routing (Traffic Flow Only)
• Latency-based Routing
• Multivalue Answer Routing
• Weighted Routing

Failover Routing

Failover routing lets you route traffic to a resource when the resource is healthy or to a different resource when the first resource is unhealthy. The primary and secondary resource record sets can route traffic to anything from an Amazon S3 bucket that is configured as a website to a complex tree of records. For more information, see Configuring Active-Passive Failover by Using Amazon Route 53 Failover and Failover Alias Records and Configuring Failover in a Private Hosted Zone.

Geolocation Routing

Geolocation routing lets you choose the resources that serve your traffic based on the geographic location of your users, meaning the location that DNS queries originate from. For example, you might want all queries from Europe to be routed to an ELB load balancer in the Frankfurt region.

When you use geolocation routing, you can localize your content and present some or all of your website in the language of your users. You can also use geolocation routing to restrict distribution of content to only the locations in which you have distribution rights. Another possible use is for balancing load across endpoints in a predictable, easy-to-manage way, so that each user location is consistently routed to the same endpoint.

You can specify geographic locations by continent, by country, or by state in the United States. If you create separate records for overlapping geographic regions—for example, one record for North America and one for Canada—priority goes to the smallest geographic region. This allows you to route some queries for a continent to one resource and to route queries for selected countries on that continent to a different resource. (For a list of the countries on each continent, see Location.)

Geolocation works by mapping IP addresses to locations. However, some IP addresses aren't mapped to geographic locations, so even if you create geolocation resource record sets that cover all seven continents, Amazon Route 53 will receive some DNS queries from locations that it can't identify. You can create a default record that handles both queries from IP addresses that aren't mapped to any location and queries that come from locations that you haven't created geolocation records for. If you don't create a default record, Amazon Route 53 returns a "no answer" response for queries from those locations.

To improve the accuracy of geolocation routing, Amazon Route 53 supports the edns-client-subnet extension of EDNS0. (EDNS0 adds several optional extensions to the DNS protocol.) Amazon Route 53 can use edns-client-subnet only when DNS resolvers support it:

• When a browser or other viewer uses a DNS resolver that does not support edns-client-subnet, Amazon Route 53 uses the source IP address of the DNS resolver to approximate the location of the user and responds to geolocation queries with the DNS record for the resolver's location.
• When a browser or other viewer uses a DNS resolver that does support edns-client-subnet, the DNS resolver sends Amazon Route 53 a truncated version of the user's IP address. Amazon Route 53 determines the location of the user based on the truncated IP address rather than the source IP address of the DNS resolver; this typically provides a more accurate estimate of the user's location. Amazon Route 53 then responds to geolocation queries with the DNS record for the user's location.

For more information about edns-client-subnet, see the IETF draft Client Subnet in DNS Requests.

Geoproximity Routing (Traffic Flow Only)

Geoproximity routing lets Amazon Route 53 route traffic to your resources based on the geographic location of your resources. You can also optionally choose to route more traffic or less to a given resource by specifying a value, known as a bias, that expands or shrinks the size of the geographic region from which traffic is routed to a resource.

To use geoproximity routing, you must use Amazon Route 53 traffic flow. You create geoproximity rules for your resources and specify one of the following values for each rule:

• If you're using AWS resources, the AWS Region that you created the resource in
• If you're using non-AWS resources, the latitude and longitude of the resource

To optionally expand the size of the geographic region from which Amazon Route 53 routes traffic to a resource, specify a positive integer from 1 to 99 for the bias. Amazon Route 53 shrinks the size of adjacent regions. When you specify a negative bias of -1 to -99, the opposite is true. The effect of changing the bias for your resources depends on a number of factors, including the following:

• The number of resources that you have.
• How close the resources are to one another.
• The number of users that you have near the border area between geographic regions. For example, if you have resources in Boston and Washington, DC and you have a lot of users in New York City, which is roughly equidistant between your resources, a small change in bias could result in a large swing in traffic from resources in Boston to resources in DC or vice versa.

We recommend that you change the bias in small increments to prevent overwhelming your resources due to an unanticipated swing in traffic.

Latency-based Routing

If your application is hosted in multiple Amazon EC2 regions, you can improve performance for your users by serving their requests from the Amazon EC2 region that provides the lowest latency.

To use latency-based routing, you create latency records for your resources in multiple EC2 Regions. When Amazon Route 53 receives a DNS query for your domain or subdomain (example.com or apex.example.com), it determines which Amazon EC2 regions you've created latency records for, determines which region gives the user the lowest latency, and then selects a latency record for that region. Amazon Route 53 responds with the value from the selected record, such as the IP address for a web server.

For example, suppose you have ELB load balancers in the US West (Oregon) Region and in the Asia Pacific (Singapore) Region. You created a latency record for each load balancer. Here's what happens when a user in London enters the name of your domain in a browser:

1. DNS routes the request to an Amazon Route 53 name server.
2. Amazon Route 53 refers to its data on latency between London and the Singapore region and between London and the Oregon region.
3. If latency is lower between the London and Oregon regions, Amazon Route 53 responds to the query with the IP address for the Oregon load balancer. If latency is lower between London and the Singapore region, Amazon Route 53 responds with the IP address for the Singapore load balancer Singapore.

Latency between hosts on the internet can change over time as a result of changes in network connectivity and routing. Latency-based routing is based on latency measurements performed over a period of time, and the measurements reflect these changes. A request that is routed to the Oregon region this week might be routed to the Singapore region next week.

Note

When a browser or other viewer uses a DNS resolver that supports the edns-client-subnet extension of EDNS0, the DNS resolver sends Amazon Route 53 a truncated version of the user's IP address. If you configure latency-based routing, Amazon Route 53 considers this value when routing traffic to your resources.

Multivalue Answer Routing

Multivalue answer routing lets you configure Amazon Route 53 to return multiple values, such as IP addresses for your web servers, in response to DNS queries. You can specify multiple values for almost any record, but multivalue answer routing also lets you check the health of each resource, so Amazon Route 53 returns only values for healthy resources. It's not a substitute for a load balancer, but the ability to return multiple health-checkable IP addresses is a way to use DNS to improve availability and load balancing.

To route traffic approximately randomly to multiple resources, such as web servers, you create one multivalue answer record for each resource and, optionally, associate an Amazon Route 53 health check with each record. Amazon Route 53 responds to DNS queries with up to eight healthy records and gives different answers to different DNS resolvers. If a web server becomes unavailable after a resolver caches a response, client software can try another IP address in the response.

Note the following:

• If you associate a health check with a multivalue answer records, Amazon Route 53 responds to DNS queries with the corresponding IP address only when the health check is healthy.
• If you don't associate a health check with a multivalue answer record, Amazon Route 53 always considers the record to be healthy.
• If you have eight or fewer healthy records, Amazon Route 53 responds to all DNS queries with all the healthy records.
• When all records are unhealthy, Amazon Route 53 responds to DNS queries with up to eight unhealthy records.

Weighted Routing

Weighted routing lets you associate multiple resources with a single domain name (example.com) or subdomain name (acme.example.com) and choose how much traffic is routed to each resource. This can be useful for a variety of purposes, including load balancing and testing new versions of software.

To configure weighted routing, you create resource record sets that have the same name and type for each of your resources. You assign each record a relative weight that corresponds with how much traffic you want to send to each resource. Amazon Route 53 sends traffic to a resource based on the weight that you assign to the record as a proportion of the total weight for all records in the group:

For example, if you want to send a tiny portion of your traffic to one resource and the rest to another resource, you might specify weights of 1 and 255. The resource with a weight of 1 gets 1/256th of the traffic (1/1+255), and the other resource gets 255/256ths (255/1+255). You can gradually change the balance by changing the weights. If you want to stop sending traffic to a resource, you can change the weight for that record to 0.