When it comes to protecting your infrastructure, securing the network comes into consideration first. The physical security of your IT infrastructure in the data center is to be taken care of by providers. In the case of cloud-like AWS providers, they take the utmost care of the physical security of your infrastructure. Let's talk about ensuring network security, which is your responsibility as an application owner.
To understand it better, let's take an example from a public cloud provider such as AWS and apply the same example to your on-premises or private cloud network infrastructure as well. As illustrated in the following diagram, you should apply security at every layer and define trusted boundaries around each layer, with minimal access:
In the preceding diagram, the load balancer is in a public subnet, which can accept internet traffic and distribute it to the application server...