For the last 5 years, I've managed an e-commerce website grossing 7 figures yearly. Here are the tools I've set up to ensure everything runs smoothly:

Build via Bash

The scripts automate the build sequence: pulling all the code updates and translations, checking code quality, running automated tests and then handing over to GitHub actions for CI/CD.

Deploy using GitHub actions / AWS

Github actions then also run automated tests, set the environment variables, zip the code and push it to AWS to deploy it.

Observe via Sentry

Sentry is a lifesaver: any crashes (either frontend or backend) are logged to Sentry, which allows us to 1/ quickly find the cause when users report an error and 2/ do triage based on which errors are the most common

Alerts via Slack

All the tools (except for the initial build scripts) let us know via Slack when something is going on / going wrong. (And internal users can also trigger reports via Slack)

All these tools help me sleep at night - because they automate all the boring bits and let me know when there is anything I need to take a look at.