Apply Custom Fermyon Subdomain

Every Spin application running on Fermyon Cloud receives a domain name that has the following format: <your-App-Name-randomlyAssignedString> For a more easily recognizable domain name, you may want to change your Spin application’s domain name from to

Custom Fermyon subdomain names allow you to rename the <your-App-Name-randomyAssignedString> subdomain. This custom Fermyon subdomain will be combined with the apex domain to give your application a complete domain name.


Log into Fermyon Cloud and ensure you have a Spin application running on Fermyon Cloud. If you do not have a Spin application yet, follow our quickstart guide to deploy one.

Cloud UI with 1 application

Select Your Spin Application

Select the application whose domain name you intend to modify. Then select the Edit Subdomain Name button in the top right corner.

Cloud UI with app panel view open

Apply New Custom Fermyon Domain

In the text box, you will see your application’s current subdomain, followed by the apex domain

Custom subdomain panel with original subdomain

Input your preferred subdomain name that meets the following characteristics:

  • character length is at least 3
  • character length is less than 63 characters
  • subdomain name is unique

Then click save to apply your changes.

Custom subdomain panel with new subdomain

Validate Custom Fermyon Subdomain Name

If you view the application’s domain name in the panel view, you should see it has been updated to reflect your custom Fermyon subdomain name.

App panel view with custom subdomain name

Visit the application’s domain name to validate the change has been applied successfully.

$ curl

Spin app responding at

Next Steps

Congratulations, you have successfully applied a custom Fermyon subdomain to your Spin application.