PM2 for process management in Express - Step-by-Step Execution

Concept Flow - PM2 for process management

Start Node.js app with PM2

↓

PM2 launches app process

↓

PM2 monitors process health

↓

If crash or stop detected

↓

PM2 restarts app automatically

↓

User can manage app via PM2 commands

↓

Stop, restart, list, logs, scale processes

PM2 runs your Node.js app, watches it, and restarts it if it crashes, letting you control it easily.

Execution Sample

Express

pm2 start app.js
pm2 list
pm2 restart app
pm2 stop app
pm2 logs

These commands start, list, restart, stop, and show logs of your app managed by PM2.

Execution Table

Step	PM2 Command	Action Taken	Process Status	Output/Result
1	pm2 start app.js	Launch app.js as a managed process	online	Process started with id 0
2	pm2 list	Show all managed processes	online	List shows app.js with status online
3	app.js crashes	PM2 detects crash	stopped	Process exited unexpectedly
4	PM2 auto-restarts app.js	Restart process automatically	online	Process restarted with id 0
5	pm2 restart app	User restarts app manually	online	Process restarted successfully
6	pm2 stop app	User stops app process	stopped	Process stopped
7	pm2 logs	Show app logs	stopped	Logs displayed in terminal

💡 User stops the app with 'pm2 stop app', process status becomes stopped, ending management session.

Variable Tracker

Variable	Start	After Step 1	After Step 3	After Step 4	After Step 6
Process Status	none	online	stopped (crash)	online (auto-restart)	stopped (manual stop)

Key Moments - 3 Insights

Why does PM2 restart the app automatically after a crash?

PM2 monitors the process status and when it detects a crash (see step 3 in execution_table), it restarts the app automatically (step 4) to keep it running without manual intervention.

What is the difference between 'pm2 stop' and a crash?

'pm2 stop' is a manual command by the user to stop the app (step 6), while a crash is an unexpected failure detected by PM2 (step 3). The app status changes to 'stopped' in both, but only crashes trigger automatic restarts.

How can you see the current status of your app processes?

Using 'pm2 list' (step 2) shows all managed processes and their statuses, helping you know if apps are online or stopped.

Visual Quiz - 3 Questions

Look at the execution_table, what is the process status immediately after the app crashes?

A online

B starting

C stopped

D restarting

💡 Hint

Check step 3 in the execution_table where the crash is detected.

At which step does PM2 automatically restart the app after a crash?

A Step 3

B Step 4

C Step 2

D Step 6

💡 Hint

Look for the step where the action says 'Restart process automatically'.

If you run 'pm2 stop app', what will be the process status shown in variable_tracker after that?

A stopped

B online

C crashed

D starting

💡 Hint

Refer to the 'After Step 6' column in variable_tracker for Process Status.

Concept Snapshot

PM2 manages Node.js apps by running them as processes.
It watches for crashes and restarts apps automatically.
Use commands like 'pm2 start', 'pm2 stop', 'pm2 restart', and 'pm2 logs'.
Check status anytime with 'pm2 list'.
This keeps your app running smoothly without manual restarts.

Full Transcript

PM2 is a tool that helps you run and manage your Node.js apps easily. When you start your app with PM2, it runs the app as a process and watches it closely. If the app crashes, PM2 notices and restarts it automatically so your app stays online. You can control your app with simple commands like 'pm2 start' to launch it, 'pm2 stop' to stop it, 'pm2 restart' to restart it, and 'pm2 logs' to see what your app is doing. You can also see all running apps and their status with 'pm2 list'. This way, PM2 helps keep your app running smoothly without you needing to watch it all the time.