My disappointment with Rust, that in no way diminishes how much I enjoy using it in my own time, is that I have a hard time recommending it for microservices, which are arguably an average project at an average company. The ecosystem just doesn't feel as fleshed out or complete as in Go. It's a shame because there's libraries in Rust that I adore like clap, serde, and diesel but when I last wanted to write something that integrates with AWS, I found a deprecated unofficial crate and a non-production-ready official crate from AWS.

I don't know whether to attribute this disappointment to the breadth of what Rust can be used for and the difficulty in doing all of them well, or a lack of wider/corporate buy-in for these use cases. It's a pity, because after getting past the initial learning curve I struggle to find anything wrong with the language itself.

FWIW, AWS now have an official SDK for Rust in beta:

https://aws.amazon.com/sdk-for-rust/

There are people at Microsoft working on a Rust SDK for Azure, but it's explicitly a volunteer effort with no support guarantees at the moment:

https://github.com/Azure/azure-sdk-for-rust

These days I probably would not look at any language that did not have SDKs for AWS and Azure, for similar reasons.

What tools or libraries is Rust missing for building microservices?

They already mentioned AWS support was poor, which I can't confirm. I can say that GCP support is subpar. Comparing Python's GCP library with Rust's is a world of difference.