Pulumi vs. Cloud SDKs (AWS Boto, etc.)
It’s important to realize that these libraries are fundamentally different in their aim, compared to Pulumi. These libraries give direct access to the cloud APIs and, though they can be used to provision resources, they leave it to the programmer to do so reliably. Because these are imperative libraries, attempting to open code provisioning and updates using them are error-prone (usually devolving into a custom, homegrown provisioning system).
Pulumi uses a true infrastructure-as-code to ensure robust management of resources. In particular, should an update fail, your system is always in a well defined, recoverable state, compared to ad-hoc and manual recovery.
In fact, Pulumi internally uses such libraries when interfacing with the different cloud providers. It’s all the things on top – the language runtime, the ability to diff updates, the concurrency management and robust checkpointing of state – that makes Pulumi different. If you wanted repeatable and robust deployments in a team environment, you’d need to build all of this yourself on top of these cloud SDKs. And multi-cloud would require a considerable amount of effort, and would be tantamount to building another Pulumi by hand.