From the Azure Portal, on the Configure Tab for a notification hub I am able to generate a primary key and secondary key. I understand these are required to gain programmatic access to the Azure API - allowing my client app to create registrations and send messages.
Could anyone please explain:
Why are there two keys (primary and secondary)? Do the keys generated from this UI expire and if so how long do they live before expiry?
They don't expire. The reason there are two is because it's recommended that you regenerate the keys periodically for security reasons. For example, suppose your application is using the primary key today. If you regenerated the primary key, then your application would be broken until you could update it and resulting in downtime. Instead, you can change your application to use the secondary key with basically little or no downtime. Then, after your application has been updated, you can regenerate the primary key. Next month (or whatever schedule you like), you can repeat the process, switching back to the primary key and regenerating the secondary key.
This is not unique to Notification Hubs. You will see primary and secondary keys in other services such as Storage and Media Services. The idea is the same.
