In the beginning there were servers, and they had a fixed cost per month. You ordered a certain spec and had a fixed price which was predictable every month. Sometimes you might exceed your bandwidth allowance but most hosting companies included a huge allowance so that was unlikely.
Regardless of how little or how much traffic served and activity performed, the cost remained the same.
For many early switchers to the cloud, the cost remained somewhat fixed. Although you didn’t contract a known price up front (before instance reservations), if you were just using VMs (probably on EC2) then you were still paying a fixed fee.
Network usage was the first real “pay as you go” element for most people moving to the cloud. Both public and private traffic was billed for precisely the amount used, which might have been a nice reduction but was probably a nasty surprise.
Moving from fixed, all inclusive contracts to pay as you go removes a safety net which makes you responsible for optimising your network usage whether it is wanted or not. You no longer have control over spikes and have to pay for sudden popularity or malicious attacks.
This is quite a drastic change of mindset, particularly with regards internal traffic. Verbose network protocols such as for database replication or queuing systems suddenly have a real impact on your budgeting, yet they are very difficult to predict because they’re out of your control.
But that’s just the beginning.
For new cloud-first architectures, every single element of your architecture is billed on a usage basis. Every message in a queue. Every row in a database. Every serverless function call. You can just as easily save a lot of money on low traffic applications as blow through your budget with highly trafficked systems, poor design or bugs.
For developers, this means efficiency matters again. Performance improvements have a direct impact on the bottom line and developer time spend on optimising and refactoring can now be given a dollar value.
The gain is in handing the undifferentiated heavy lifting to a cloud service. Instead of spending time reinventing a standardized component, time can now be spent on the core application code that differentiates you service.
DevOps no longer really means developers understanding how to operate their applications. It’s more about how their applications operate in terms of performance, and therefore cost.
This is quite a shift in mindset.