PM2 for process management in Node.js - Step-by-Step Execution

Concept Flow - PM2 for process management

Start Node.js app with PM2

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PM2 launches app process

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PM2 monitors process health

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If process crashes

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PM2 restarts process automatically

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User can check status with PM2 commands

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User can stop/restart/delete process

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Exit

PM2 starts and monitors Node.js apps, restarts them if they crash, and lets users control processes with commands.

Execution Sample

Node.js

pm2 start app.js
pm2 status
pm2 restart app
pm2 stop app
pm2 delete app

These commands start, check, restart, stop, and delete a Node.js app process managed by PM2.

Execution Table

Step	Command	PM2 Action	Process State	Output/Result
1	pm2 start app.js	Launch app.js as a managed process	Running	Process started with id 0
2	pm2 status	Show all managed processes	Running	List shows app.js with status 'online'
3	app.js crashes	PM2 detects crash	Stopped briefly	PM2 restarts app.js automatically
4	pm2 restart app	Restart app process	Running	Process restarted successfully
5	pm2 stop app	Stop app process	Stopped	Process stopped
6	pm2 delete app	Remove app from PM2 list	Not running	Process deleted from PM2
7	pm2 status	Show all managed processes	No app process	Empty list or no app.js found

💡 Process deleted, no longer managed by PM2, so status shows no app running

Variable Tracker

Variable	Start	After Step 1	After Step 3	After Step 4	After Step 5	After Step 6
Process State	Not running	Running	Restarting (after crash)	Running	Stopped	Deleted

Key Moments - 3 Insights

Why does PM2 restart the app automatically after a crash?

PM2 monitors the process health and restarts it immediately when it detects a crash, as shown in step 3 of the execution_table.

What happens if you delete a process from PM2?

Deleting removes the process from PM2's management list, so it no longer monitors or controls it, as seen in step 6 and 7.

How can you check if your app is running under PM2?

Use 'pm2 status' command to see all managed processes and their states, demonstrated in steps 2 and 7.

Visual Quiz - 3 Questions

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

A Deleted

B Stopped briefly

C Running

D Not running

💡 Hint

Check step 3 in the execution_table under 'Process State'

At which step does PM2 remove the app from its management list?

A Step 2

B Step 4

C Step 6

D Step 5

💡 Hint

Look at the 'Command' and 'PM2 Action' columns in the execution_table

If you run 'pm2 stop app' instead of 'pm2 delete app', what will be the process state?

A Stopped

B Running

C Deleted

D Restarting

💡 Hint

Refer to step 5 in the execution_table for 'pm2 stop app' command

Concept Snapshot

PM2 manages Node.js apps by running them as processes.
It monitors and restarts apps if they crash.
Use 'pm2 start <app>' to launch.
Check status with 'pm2 status'.
Stop with 'pm2 stop <app>' and remove with 'pm2 delete <app>'.

Full Transcript

PM2 is a tool to manage Node.js applications by running them as background processes. When you start an app with PM2, it launches the app and keeps it running. If the app crashes, PM2 automatically restarts it to keep it alive. You can check the status of all apps managed by PM2 using the 'pm2 status' command. To stop an app, use 'pm2 stop', and to remove it completely from PM2's control, use 'pm2 delete'. This way, PM2 helps keep your apps running smoothly without manual restarts.