PM2 for process management in Node.js - Practice Problems & Coding Challenges

Challenge - 5 Problems

🧠 Conceptual

intermediate

What is the primary purpose of PM2 in Node.js?

PM2 is a popular tool used with Node.js. What is its main job?

A To convert Node.js applications into mobile apps automatically.

B To compile Node.js code into machine language for faster execution.

C To provide a graphical user interface for writing Node.js code.

D To manage and keep Node.js applications running smoothly in the background.

💡 Hint

Think about what helps keep your app alive and restarts it if it crashes.

PM2 is a process manager that runs Node.js apps continuously, restarts them on failure, and helps manage multiple apps.

❓ component_behavior

intermediate

What happens when you run 'pm2 start app.js'?

Consider you have a Node.js app in app.js. What does the command pm2 start app.js do?

A Only runs the app once and then stops PM2 automatically.

B Starts the app and keeps it running in the background, restarting if it crashes.

C Compiles <code>app.js</code> into a binary file without running it.

D Deletes <code>app.js</code> after running it once.

💡 Hint

Think about how PM2 helps keep your app alive even if it crashes.

The command starts the app under PM2's control, so it runs in the background and restarts if it stops unexpectedly.

❓ state_output

advanced

What is the output of 'pm2 list' after starting two apps?

You started two apps with PM2: pm2 start app1.js and pm2 start app2.js. What will pm2 list show?

A A table listing both apps with their status as 'online' and their process IDs.

B An error saying no apps are running because PM2 does not track multiple apps.

C Only the first app listed with the second app missing.

D A blank screen with no output.

💡 Hint

PM2 tracks all apps it manages and shows their status.

The pm2 list command shows all running apps managed by PM2 with details like status and IDs.

🔧 Debug

advanced

Why does 'pm2 restart app' fail with 'process not found'?

You ran pm2 restart app but got an error: 'process not found'. What is the likely cause?

A The process name 'app' does not match any running PM2 process names or IDs.

B PM2 is not installed on your system.

C Your Node.js app crashed and cannot be restarted.

D You need to use <code>pm2 reload app</code> instead of restart.

💡 Hint

Check the exact process names or IDs PM2 shows in pm2 list.

The error means PM2 cannot find a process named 'app'. You must use the exact name or ID shown by PM2.

📝 Syntax

expert

Which PM2 ecosystem config file is valid for running two apps?

Choose the correct JSON format for a PM2 ecosystem file that runs app1.js and app2.js with names app-one and app-two.

A

{
  "apps": {
    "app-one": "app1.js",
    "app-two": "app2.js"
  }
}

B

}
]  
}"sj.2ppa" :"tpircs" ,"owt-ppa" :"eman"{    
,}"sj.1ppa" :"tpircs" ,"eno-ppa" :"eman"{    
[ :"sppa"  
{

C

{
  "apps": [
    {"name": "app-one", "script": "app1.js"},
    {"name": "app-two", "script": "app2.js"}
  ]
}

D

{
  "apps": [
    {"name": "app-one", "script": "app1.js"},
    {"name": "app-two"}
  ]
}

💡 Hint

Remember JSON requires double quotes around keys and strings, and arrays use square brackets.

Option C is valid JSON with an array of app objects each having a name and script. Others have syntax errors or missing fields.