In section 1.3.1 of Getting Started (with 3scale), i.e. Initial configurations for your API, there's a note where one can read:

To have OpenShift accept the routes created by Zync, the labels must have a maximum of 63 characters, including the dashes shown in the patterns. Hence, when you specify a system_name, you must consider the limit in the number of characters for the patterns previously described.

This will no longer be true once https://github.com/3scale/porta/pull/2083 gets merged. The PR introduces a "URL shortener" functionality that will automatically adjust hostname endpoints generated for hosted API products, based on the templates stated mentioned in the doc.

Whenever an auto-generated URL label is detected to exceed the 63-char limit, system will shorten the label to the following format: <truncated-label>-<unique-hash>, where <truncated-label> is the first 54 or 55 characters of the URL label that originally exceeded the 63-char limit and <unique-hash> is the first 7 characters of a unique SHA-1 hash calculated from the original label.

For example, a service whose system name is "my-very-long-system-name", of a tenant whose name is "Also very long tenant name" would cause an original APIcast staging endpoint "https://my-very-long-system-name-also-very-long-tenant-name-apicast-staging.3scale.net", since the URL label "my-very-long-system-name-also-very-long-tenant-name-apicast-staging" exceeds the 63-char limit (it has 67), the URL will be shortened to "https://my-very-long-system-name-also-very-long-tenant-name-api-72588d2.3scale.net".

The URL shortener only works for system-generated service endpoints, i.e., URLs manually introduced by the user for self-managed services will not be affected, and therefore it remains the customer's responsibility to comply with constraints imposed by RFC-1035.