Data centers connect to the internet through fiber optic cables and they have more than one ISP or internet service provider that connects to the data center for both incoming and outgoing traffic.
The data has multiple connections to the internet through Fiber Optic Internet lines to ensure they have internet service at all times should one connection go down.
Then the internet traffic can be routed through the other lines in the even of an internet outage.
The Fiber Optic Internet connects to the data centers through massive fiber optic lines and then those lines connect to the servers through larger internet routers and switches.
The internet for a data center connects almost the same as your home internet but on a more massive scale.