Dr. DNS -- Dynamic DNS for AWS

Dr. DNS is a serverless app providing dynamic DNS on AWS. EC2 instances tagged with a Name that matches one of your domains in Route 53 will automatically have entries created (and removed) for them on startup (and shutdown/stop).

Tags Used & How They Are Used

Name = something.example.com

Records created are <instance-id>.something.example.com and something.example.com. If multiple hosts have the same name, they will each have a unique record <instance-id>.something.example.com and something.example.com will round-robin between them. As a special case, if Name already includes the instance ID, like <instance-id>.a.b.c, then it is treated as though it were just the base name: a record is created for <instance-id>.a.b.c pointing only at the instance, and a round-robin record is created at a.b.c. The Name tag thus behaves ergonomically when used with either individual instances or auto-scaling groups.

dns:fqdn = name.example.com, dns:fqdn:... = name.example.com

One or many DNS names can be assigned to an instance with the tag dns:fqdn and tags prefixed with dns:fqdn: (like: dns:fqdn:1, dns:fqdn:2). These names are used exactly as given.

dns:base = group.example.com, dns:base:... = group.example.com

When the tag dns:base or a tag prefixed with dns:base: (like: dns:base:1, dns:base:2) is specified, two records are created: a round-robin record like group.example.com which points to all instances sharing the same base, and a record <instance-id>.group.example.com pointing to just that specific instance. This is especially useful with auto-scaling groups.

When tags are assigned to an auto-scaling group, they can be automatically inherited by the instances in the group. This works well with the Name and dns:base and dns:base:... style tags. To enable tagging of instances, check the Tag New Instances option in the Amazon console or set PropagateAtLaunch from the AWS APIs when creating the group.

The tags are always weighted records, identified by the instance ID, even when they point directly to the instance, to ensure that Dr. DNS updates and deletes only a very narrow selection of records.

Setup with Cloud Formation Template

Setting up the permissions and event streams for a serverless application is almost as much work as writing the application itself. The Cloud Formation template sets up the Lambda and provides it with appropriate permissions and event streams for instances launched in EC2 directly or by way of an auto-scaling group:

View in the CloudFormation template designer.

Frequently Asked Questions

What kinds of records does Dr. DNS create?

Dr. DNS creates members of "weighted record sets", identified by the instance ID, even when they point directly to the instance, to ensure that only a narrow band of records are ever updated or deleted.

What is the target of the records created by Dr. DNS?

The EC2 instance's public DNS name is used in preference to the private DNS name, where available.

How does Dr. DNS handle invalid DNS names in tags?

If a tag does not match the domain name syntax restrictions, Dr. DNS logs as much and returns early.

How does Dr. DNS know which domain in which to place a record?

The domain or domains with the longest suffix match on a record name are used to store the record.