ttl

The amount of time, in seconds, that you want DNS resolvers to cache the settings for this record.

Alias records don't include a TTL because Route 53 uses the TTL for the Amazon Web Services resource that an alias record routes traffic to. If you include the AWS_ALIAS_DNS_NAME attribute when you submit a RegisterInstance request, the TTL value is ignored. Always specify a TTL for the service; you can use a service to register instances that create either alias or non-alias records.