How I Hardened an Ubuntu Server After Security Alerts Started Showing Up

A while ago, I was asked to check one of our Ubuntu servers because the cloud dashboard had started showing a lot of security alerts. Nothing was visibly broken. The apps were still running. Docker containers were still up. Nginx was still serving traffic. But the security panel was reporting things like: intrusion attempts multiple vulnerabilities outdated packages suspicious SSH activity That kind of dashboard can make anyone nervous. The first thought is usually: “Did someone already get into