Day 11: Deploying Java WAR to Tomcat and Attaching AWS ENI Explained Simply

A hands-on DevOps learning exercise on Day 11 covered two practical tasks: deploying a Java web application to Apache Tomcat on Linux and attaching a secondary Elastic Network Interface (ENI) to an AWS EC2 instance. Deploying to Tomcat requires only copying a WAR file into the webapps directory, after which Tomcat automatically detects, expands, and serves the application. On the AWS side, an ENI functions as a movable virtual network card that retains its private IP, Elastic IP, MAC address, and security groups even when detached from one instance and reattached to another. This portability makes ENIs useful for failover scenarios, where network identity can be shifted to a standby instance without requiring upstream configuration changes. Both tasks, sourced from the KodeKloud Engineer platform, highlight how foundational cloud and Linux operations are often simpler in practice than commonly assumed.