The infrastructure layer provides support to all the other layers and is responsible for communication between the other layers, for example, interaction with databases, message brokers, file systems, and so on. It contains the supporting libraries that are used by the other layers. It also implements the persistence of business objects.

To understand the interaction of the different layers, let's use an example of booking a table at a restaurant. The end user places a request for a table booking using the UI. The UI passes the request to the application layer. The application layer fetches domain objects, such as the restaurant, the table, a date, and so on, from the domain layer. The domain layer fetches these existing persisted objects from the infrastructure and invokes relevant methods to make the booking and persist them back to the infrastructure layer. Once domain objects are persisted, the application layer shows the booking confirmation to the end user.

https://aws.amazon.com/compliance/data-center/infrastructure-layer/#:~:text=The%20Infrastructure%20Layer%20is%20the,servers%20and%20ultimately%20your%20data.