Use what you learned in the previous lesson to solve real-world problems.

Check what you understood with a short quiz.

Compare localhost, private addresses, and public addresses so you can tell whether an app is reachable only from the same machine, from a network, or from the internet.

Use what you learned in the previous lesson to solve real-world problems.

Reason through why an app needs files on disk: executable code, static assets, templates, uploaded content, and local data each behave differently when the app runs.

Use what you learned in the previous lesson to solve real-world problems.

Check what you understood with a short quiz.

Use environment variables as runtime settings, such as database URLs, feature flags, or secret names, without hard-coding them into the application.

Use what you learned in the previous lesson to solve real-world problems.

Recognize how apps connect to outside dependencies like databases, caches, message queues, and third-party APIs, and why those addresses and credentials are usually configuration.

Use what you learned in the previous lesson to solve real-world problems.

Check what you understood with a short quiz.

Read the difference between logs written to standard output and logs written to files, and use log lines to reconstruct what an app did before a failure.

Use what you learned in the previous lesson to solve real-world problems.

Interpret common process endings: a clean shutdown, a crash, a nonzero exit code, or a kill signal from the operating system.

Use what you learned in the previous lesson to solve real-world problems.

Check what you understood with a short quiz.

Walk through how a service manager such as systemd keeps an app running by starting it at boot, restarting it after crashes, and recording its status.

Use what you learned in the previous lesson to solve real-world problems.

Identify what makes a running app unhealthy even if its process still exists, such as a stuck request handler, full disk, broken dependency, or exhausted memory.

Use what you learned in the previous lesson to solve real-world problems.

Check what you understood with a short quiz.

Reason about CPU, memory, disk, and file descriptor limits so you can predict why one busy app can slow down or break other work on the same server.

Use what you learned in the previous lesson to solve real-world problems.

Compare graceful shutdown with abrupt termination: see how an app stops accepting new work, finishes in-flight requests, closes connections, and exits safely.

Use what you learned in the previous lesson to solve real-world problems.

Check what you understood with a short quiz.

Review this chapter with practice based on your mistakes.