How to manage Enterprise Distribution certificate expiration?

Question

Our customer has just joined the iOS Developer Enterprise Program. They have signed the app (developed by us) with their Enterprise Distribution and installed it succesfully

Answer 1

Apple revised the documentation...

An app won’t run if its distribution certificate has expired. Currently, distribution certificates are valid for one year, and you can have two certificates active at the same time. The second certificate is intended to provide an overlapping period during which you can update your apps before the first certificate expires.

For example, six months before your distribution certificate expires, create a new certificate and use it to update your apps for the next year. To do this, you request a new distribution certificate from the iOS Dev Center (do not revoke your first certificate), use it to create new distribution provisioning profiles for each of your apps, and then you recompile and distribute the updated apps to your users. See Providing updated apps.