NodeJS

How to apply clustering using .PM2 command when running NodeJS project?

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To run a NodeJS project using the `.PM2` command which applies clustering, you would use PM2's built-in **cluster mode**. In this mode, PM2 would start many instances of your NodeJS application and distribute those instances across all CPU cores available on your machine; therefore, it makes it scale much better and can handle more requests.

Steps to Apply Clustering Using PM2

1. Install PM2 Globally

First of all, if you haven't installed PM2 globally on your system yet, install it with this npm command:

npm install pm2 -g

2. Running Your NodeJS Application in Cluster Mode

To run your application in “cluster mode”, use the following command:

pm2 start app.js -i max

Now, above, what we have done is:

- ‘app.js’: This is the file that launches your Node application.

'- ‘-i max’: The ‘-i’; flag is an abbreviation for "instances." Setting this flag to `max` instructs it to run as many instances as the number of CPU cores your machine offers. Instead, you can set an exact number of instances with the syntax: ‘-i 4’.

Example

pm2 start app.js -i max --name "my-node-app"

This will do the following:

Run `app.js` in **cluster mode**

Spawn as many instances as there are CPU cores: `max`

It will label this process as ` "my-node-app"`.

3. Display Clustered Processes

After you have started your application in cluster mode, you can see all running instances with:

pm2 list

It will display the number of running processes and show you the current status of those instances.

4. Monitoring Cluster Performance

You can view the performance and health of your running instances by issuing `monit` from your terminal:

pm2 monit

This yields a real-time view of CPU and memory usage for each instance of your app.

5. Managing the Cluster

You can manage the clusterized processes (start, stop, restart, etc.) this way:

- Stop the Application: pm2 stop my-node-app

- Restart All Instances: pm2 restart my-node-app

- Reload Without Downtime:

To reload an app with zero downtime, you can make use of: pm2 reload my-node-app

- Delete the Application: pm2 delete my-node-app

6. ecosystem.config.js" for Easier Handling

An ecosystem configuration file (ecosystem.config.js) can be created defining how PM2 should handle your app, such as clustering, environment variables, etc.

Example `ecosystem.config.js` file:

module.exports = { apps: [ { name: "my-node-app", script: "./app.js", }]instances: "max", // Number of instances (use max for auto-scaling) exec_mode: "cluster", // Enables cluster mode watch: true, // Restart app on file changes env: { NODE_ENV: "development"}, env_production: { NODE_ENV: "production" } } ]};

To start the application with this configuration, run:

pm2 start ecosystem.config.js --env production

7. Automatic Restart on Crashes

PM2 automatically restarts any crashed instances, ensuring that your app stays up and running without manual intervention.

Conclusion

Using PM2’s cluster mode improves performance by distributing the load across all available CPU cores, making your NodeJS app more scalable. You can manage these clustered instances easily through PM2's commands.

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