Amazon Cloud Map service DNS configuration - Amazon Cloud Map
Routing policyRecord type
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Amazon Cloud Map service DNS configuration

When you create a service in a namespace that supports instance discovery by DNS queries, Amazon Cloud Map creates Route 53 DNS records. You must specify a Route 53 routing policy and DNS record type that will apply to all Route 53 DNS records that Amazon Cloud Map creates.

Routing policy

A routing policy determines how Route 53 responds to the DNS queries that are used for service instance discovery. Supported routing policies and how they relate to Amazon Cloud Map are as follows.

Weighted routing

Route 53 returns the applicable value from one randomly selected Amazon Cloud Map service instance from among the instances that you registered using the same Amazon Cloud Map service. All records have the same weight, so you can't route more or less traffic to any instances.

For example, suppose the service includes configurations for one A record and a health check, and you use the service to register 10 instances. Route 53 responds to DNS queries with the IP address for one randomly selected instance from among the healthy instances. If no instances are healthy, Route 53 responds to DNS queries as if all the instances were healthy.

If you don't define a health check for the service, Route 53 assumes that all instances are healthy and returns the applicable value for one randomly selected instance.

For more information, see Weighted Routing in the Amazon Route 53 Developer Guide.

Multivalue answer routing

If you define a health check for the service and the result of the health check is healthy, Route 53 returns the applicable value for up to eight instances.

For example, suppose that the service includes configurations for one A record and a health check. You use the service to register 10 instances. Route 53 responds to DNS queries with IP addresses for only a maximum of eight healthy instances. If fewer than eight instances are healthy, Route 53 responds to every DNS query with the IP addresses for all the healthy instances.

If you don't define a health check for the service, Route 53 assumes that all instances are healthy and returns the values for up to eight instances.

For more information, see Multivalue Answer Routing in the Amazon Route 53 Developer Guide.

Record type

A Route 53 DNS record type determines the type of value Route 53 returns in response to the DNS queries that are used for service instance discovery. The different DNS record types you can specify, and the associated values returned by Route 53 in response to queries are as follows.

A

If you specify this type, Route 53 returns the IP address of the resource in IPv4 format, such as 192.0.2.44.

AAAA

If you specify this type, Route 53 returns the IP address of the resource in IPv6 format, such as 2001:0db8:85a3:0000:0000:abcd:0001:2345.

CNAME

If you specify this type, Route 53 returns the domain name of the resource (such as www.example.com).

Note

  • To configure a CNAME DNS record, you must specify the Weighted routing routing policy.

  • When you configure a CNAME DNS record, you can't configure a Route 53 health check.

SRV

If you specify this type, Route 53 returns the value for an SRV record. The value for an SRV record uses the following values:

priority weight port service-hostname

Consider the following:

  • The values of priority and weight are both set to 1 and can't be changed.

  • For port, Amazon Cloud Map uses the value that you specify for Port (AWS_INSTANCE_PORT) when you register an instance.

  • The value of service-hostname is a concatenation of the following values:

    • The value that you specify for Service instance ID (InstanceID) when you register an instance

    • The name of the service

    • The name of the namespace

    For example, suppose you specify test as an instance ID when you register an instance. The name of the service is backend and the name of the namespace is example.com. Amazon Cloud Map assigns the following value to the service-hostname attribute in the SRV record:

    test.backend.example.com

Note

If you specify values an IPv4 address, an IPv6 address, or both when you register an instance, Amazon Cloud Map automatically creates A and/or AAAA records that have the same name as the value of service-hostname in the SRV record.

You can specify record types in the following combinations:

  • A

  • AAAA

  • A and AAAA

  • CNAME

  • SRV

If you specify A and AAAA record types, you can specify an IPv4 IP address, an IPv6 IP address, or both when you register an instance.