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Migrate to the external-domain service

August 16, 2021

Who is this for?

This post is for all users of the cdn-route or custom-domain services.


The custom-domain and cdn-route services leverage Let’s Encrypt to provision certificates on our users’ behalf. Several months ago, Let’s Encrypt announced that they’re deprecating their v1 API. To work with their new API, we’ve written a replacement to the cdn-route and custom-domain services, the external-domain service. We now need to migrate your service instances to the new service to ensure their certificates can continue renewing without issue. To accomplish this, we’ve written internal tooling to migrate instances automatically without service interruption, but it does require some action on your part to initiate the migration.

What you need to do

The new external-domain service uses a different method of validation with Let’s Encrypt. The new method relies on specific DNS records being present for each of your domains. To begin the migration, you need to have configured the following DNS records for each domain on your custom-domain or cdn-route instances.

Type Name Value
CNAME _acme-challenge.$DOMAIN _acme-challenge.$

The _acme-challenge.$DOMAIN CNAME record allows us to provision SSL certificates on your behalf.

As an example, if you have a custom-domain service created for, you’d want to create a CNAME record with value

The $DOMAIN CNAME is responsible for routing the user traffic to your site. Using the example above, this would be

If you already have CNAME, A, and/or AAAA (with ALIAS) record(s) for $DOMAIN, you should update the value or replace the record to match what is shown above.

* If your domain is an “apex domain” or “2nd level domain” (i.e. instead of you will need to use an A and AAAA (with ALIAS) record(s) assuming your DNS provider supports it.

Note that the second update here changes how users get to your site. We’ve made every effort to validate we’re prepared for this change, but you should confirm that $ currently resolves before making this change.

You can do this by directly comparing the outputs of nslookup $DOMAIN and nslookup $, or by modifying your hosts file to point $DOMAIN to one of the IP addresses $ currently resolves to. If either of these tests fail, STOP and do not update your DNS, and contact support for assistance.

What to expect

During the migration

The migration will not cause:

  • downtime
  • interruption to your services
  • change in functionality or configuration to your services

During the migration, you may see a new service instance with a name you do not recognize in your space(s). Once started, the migration takes about 30 minutes for cdn-route instances, and less than 15 minutes for custom-domain instances. During this time, you will be unable to make other modifications to the service instance.

After the migration

After the migration, your service instance(s) will have a new instance ID, so any references to your service instance ID will need to be updated. Additionally, your service instance(s) will be of a different service (external-domain) and plan (domain or domain-with-cdn, depending on your current instance type).

Customers that experience issues, or that have questions about this change, can send a request to

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