Why it matters
A server that works but cannot be reached is useless. Many cloud problems are network problems: a firewall rule blocking a port, a DNS record pointing to the wrong address, a database placed where the app cannot see it. An infrastructure advert we read from a Ghanaian company named DNS, VPNs, load balancing and virtual networks. If IP addresses and DNS are new, read those IT support lessons first.
IP ranges and subnets
In the cloud you create your own private network, often called a virtual private cloud (VPC) or virtual network. You give it a range of private addresses written in CIDR notation, for example 10.0.0.0/16. The number after the slash says how many bits are fixed: a /16 holds far more addresses than a /24, which holds 256. You split the range into subnets, such as 10.0.1.0/24 for web servers and 10.0.2.0/24 for databases.
A public subnet has a route to the internet. A private subnet does not, which is where databases belong so nobody outside can reach them directly.