In PM2, a popular process manager for Node.js applications, there are two primary execution modes: Cluster mode and Fork mode. Each mode is designed to optimize the performance and scalability of Node.js applications under different conditions.
Cluster Mode
Cluster mode allows Node.js applications to run multiple instances across all available CPU cores without any modifications to the code. This mode leverages the Node.js cluster module, which enables the creation of child processes that all share server ports. It is particularly beneficial for networked applications like HTTP servers, where it can help handle an increased load by distributing incoming network requests across several instances. This distribution helps to utilize all CPU cores effectively, enhancing the application's ability to handle high traffic and improving overall response times[1][6].
For example, if you have a Node.js application that needs to handle a large number of concurrent connections or requests, you can start the application in Cluster mode with a specific number of instances using a command like pm2 start app.js -i 4, which would launch four instances of app.js[2].
Fork Mode
Fork mode, on the other hand, runs a single instance of a Node.js application as a separate child process using the child_process.fork() API. This mode is simpler and is generally used for applications that do not need to scale across multiple CPU cores. It is suitable for development environments or smaller applications where the load is not intensive and high concurrency is not required[1].
Fork mode also allows for more flexibility in terms of the executable interpreter. For instance, it can run applications written in languages other than JavaScript by specifying a different exec_interpreter (like Python or PHP). This is not possible in Cluster mode, which strictly relies on the Node.js runtime[1].
Key Differences
Concurrency and Scaling: Cluster mode is suitable for applications requi...
