Cloud Networking & Storage

The startup that got a $47,000 bill

A developer at a startup spun up a test database on AWS. He chose the wrong storage class — provisioned IOPS SSD instead of general purpose. He forgot about it. Three weeks later, the AWS bill arrived: $47,000. For a test database nobody was using.

Cloud storage is cheap. Cloud storage you do not understand is very, very expensive.

This module is the "save yourself from a surprise bill" guide. You will learn how cloud networking and storage actually work — what the options are, when to use each one, and how to avoid the mistakes that cost real money.

Cloud networking: your private internet

When you deploy an application in the cloud, it needs a network — just like your home needs Wi-Fi. But in the cloud, you build the network yourself.

Virtual Private Cloud (VPC)

A VPC is your own private section of the cloud. Think of it as renting a floor in an office building — you share the building with other tenants, but your floor is completely private. You control who gets in, where the walls go, and how rooms connect.

There Are No Dumb Questions

Why would I put anything in a private subnet?

Databases, internal APIs, and backend services should never be directly accessible from the internet. A private subnet means attackers cannot reach them even if they know the IP address. Your web server in the public subnet talks to the database in the private subnet — but the internet cannot.

What is a CIDR block?

It is a way of defining IP address ranges. 10.0.0.0/16 means "all addresses starting with 10.0" — that gives you 65,536 addresses. 10.0.1.0/24 means "all addresses starting with 10.0.1" — that gives you 256 addresses. The smaller the number after the slash, the bigger the network.

Load balancers and CDNs

Load balancers distribute incoming traffic across multiple servers. If one server is overloaded or crashes, the load balancer sends traffic to the others. Like a restaurant host seating guests at different tables instead of cramming everyone at table 1.

CDNs (Content Delivery Networks) cache your content at edge locations around the world. A user in Tokyo gets your website from a server in Tokyo, not from Virginia. Faster load times, lower bandwidth costs.

Cloud storage: where your data lives

Cloud storage comes in three flavors. Choosing the wrong one is how you get a $47,000 bill.

Object storage (S3 / Blob / GCS)

What it is: Store any file — images, videos, backups, logs — as objects in buckets. No folder hierarchy (it is faked with prefixes). Unlimited capacity.

When to use it: Static assets, backups, data lakes, website hosting, media files.

Key feature: Storage classes for cost optimization:

Block storage (EBS / Managed Disks)

What it is: Virtual hard drives that attach to virtual machines. Fast, consistent performance. Fixed size — you pay for the capacity you provision, not what you use.

When to use it: Operating system drives, databases, applications that need low-latency disk access.

The $47,000 mistake: Provisioned IOPS SSD (io1/io2) costs 10-50x more than general purpose (gp3). Only use provisioned IOPS for mission-critical databases that need guaranteed performance.

File storage (EFS / Azure Files / Filestore)

What it is: Shared file systems that multiple servers can access simultaneously. Like a shared network drive.

When to use it: Applications where multiple servers need to read/write the same files (content management, shared configurations).

Cost optimization: do not be the $47,000 guy

Key takeaways

• A VPC is your private network in the cloud — public subnets face the internet, private subnets do not
• Security groups and NACLs are your cloud firewalls — control what traffic goes where
• Object storage (S3) is for files, block storage (EBS) is for disks, file storage (EFS) is for sharing
• S3 storage classes save money: Standard for frequent access, Glacier for archives
• Load balancers distribute traffic, CDNs speed up delivery worldwide
• Set billing alerts, right-size instances, delete unused resources — 30% of cloud spend is waste
• The $47,000 bill happened because nobody understood storage types. Now you do.