Welcome to the Microsoft Q&A Platform. Thank you for reaching out & I hope you are doing well.
I understand that you would like to use path based routing for multiple backends in Azure Application gateway.
AFAIK, the /* route is not required.
You do not need to add a custom /* path rule to handle default cases. This is automatically handled by the default backend pool.
App gateway will automatically route these request to the default pool.
Please let us know if we can be of any further assistance here.
Thanks,
Kapil
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