Ask HN: How do you monitor your infrastructure's health?

What tools or services do you use or recommend to supervise the health of your server infrastructure? By health, I mean anything from testing APIs to monitoring uptime, or other general metrics that you care about with respect to the servers and services you manage.

We have a collection of about a dozen servers and another dozen API providers. We've looked at a few services like Paw (https://paw.cloud/) or Postman (https://www.getpostman.com/) for regular API testing. We've looked at services to monitor uptime. However, there are a lot!

What do you appreciate using to keep track of your stuff?