pm2

Process Graceful Reload

Process Graceful Reload

Simple Explanation:

Imagine you have a running application (like a website or a server). You made changes to the code, but you don't want to stop the application to update it. Process graceful reload allows you to seamlessly update your application with new code without interrupting its operation.

Topics in Detail:

  • Restart Mode:

    • Default: Stops the application, updates it, and restarts it.

    • Graceful: Updates the application while it's running, with no downtime.

  • Phases:

    • Prepare: The new code is loaded into memory.

    • Restart Workers: New worker processes are created with the updated code.

    • Clean: Old worker processes are terminated.

  • Max Side:

    • Configures how many worker processes can be restarted simultaneously to minimize downtime.

    • Example: pm2 start app.js --max-side 2

  • Restart Delay:

    • Specifies the delay (in seconds) between restarting workers.

    • Example: pm2 start app.js --restart-delay 5

  • Concurrency:

    • Allows multiple applications to perform graceful reload simultaneously.

    • Example: pm2 start app1.js --concurrency 2

Real-World Applications:

  • Continuous Deployment: Automatically updates applications with new code as it becomes available, minimizing downtime.

  • Rolling Updates: Gradually updates applications across multiple servers, ensuring availability during updates.

  • Testing and Experimentation: Safely deploy new code for testing or experimenting without disrupting the live application.

Improved Code Example:

pm2 start app.js --update-env --max-side 2 --restart-delay 5 --concurrency 2

This command will:

  • Start the app.js application.

  • Enable graceful reload.

  • Allow a maximum of 2 worker processes to be restarted at the same time.

  • Delay the restart by 5 seconds between workers.

  • Allow multiple applications to update concurrently.

Conclusion:

Process graceful reload is a powerful tool that enables seamless updates of applications without downtime. It is essential for continuous deployment, rolling updates, and maintain a highly available and responsive software system.

Process Monitoring

Process Monitoring with PM2

What is Process Monitoring?

Imagine your computer as a bakery. Each process is like a different type of bread being baked. Process monitoring is like checking on the ovens to make sure the bread is baking properly.

Why is Process Monitoring Important?

Just like a baker needs to check on the ovens to make sure the bread doesn't burn, process monitoring is important to make sure your programs don't crash or run into problems.

How PM2 Helps with Process Monitoring

PM2 is like a helper baker that keeps an eye on your processes and alerts you if anything goes wrong.

PM2 Monitoring Metrics

PM2 monitors several things about each process, like:

  • CPU usage: How much brain power your process is using.

  • Memory usage: How much space your process is taking up in memory.

  • Uptime: How long your process has been running without crashing.

How to Monitor Processes with PM2

To monitor your processes with PM2, you can use the pm2 monit command. This command will show you a list of all your running processes and their metrics.

pm2 monit

Real-World Applications

Process monitoring is useful in applications like:

  • Web servers: Ensuring that your website is always up and running.

  • Background workers: Monitoring tasks that run in the background and need to be kept running.

  • Databases: Checking that your database is healthy and has enough resources.

Example Code

To start monitoring a Node.js application with PM2, you can use the following code:

const pm2 = require('pm2');

pm2.start({
  name: 'my-app',
  script: 'app.js',
});

This code will start your process and make it available for monitoring with PM2.

CLI Usage

CLI Usage

1. Starting and Stopping PM2

  • pm2 start <script>: Starts a script using PM2.

  • pm2 stop <script>: Stops a script (or all scripts) managed by PM2.

  • pm2 stop <script>:<instance>: Stops a specific instance of a script.

2. Listing and Monitoring Scripts

  • pm2 list: Lists all scripts managed by PM2.

  • pm2 monit: Monitors the health and performance of your scripts.

  • pm2 logs <script>: Shows the logs for a specific script.

3. Managing Scripts

  • pm2 restart <script>: Restarts a script.

  • pm2 reload <script>: Reloads a script without restarting it (hot reload).

  • pm2 delete <script>: Deletes a script from PM2's management.

4. Advanced Features

  • pm2 ecosystem <ecosystem.config.js>: Manages multiple applications in an "ecosystem" (e.g., web servers, database).

  • pm2 hooks: Defines custom hooks to execute specific tasks before or after script actions.

  • pm2 scale <script> <n>: Scales the number of instances of a script (e.g., for load balancing).

5. Real-World Applications

  • Monitoring and management: Keep track of the health and performance of your applications in production.

  • Deployment automation: Automatically start, stop, and restart applications during deployments.

  • Load balancing: Distribute traffic across multiple instances of applications for improved performance and scalability.

Example Code

// Start a script
pm2 start server.js

// Stop all scripts
pm2 stop

// List scripts
pm2 list

// Scale an application to 4 instances
pm2 scale server 4

// Define a hook to run before starting
pm2 before-start 'echo "Starting server..."'

Installation and Setup

Installation

  • Using NPM: Run npm install pm2 -g to install PM2 globally.

  • Using Yarn: Run yarn global add pm2 to install PM2 globally.

Setup

1. Initialize PM2 Configuration:

  • Start PM2 with pm2 start.

  • Create a configuration file using pm2 config.

  • Specify settings like process names, startup scripts, and logs in the config file.

2. Manage Processes:

  • Start a process with pm2 start <process_name>.

  • Stop a process with pm2 stop <process_name>.

  • List all running processes with pm2 list.

  • Monitor process logs with pm2 logs <process_name>.

3. Process Management Options:

  • Cluster Mode: Runs multiple instances of a process for scalability.

  • Load Balancing: Distributes traffic across multiple processes.

  • Auto-Restart: Automatically restarts processes if they crash or stop unexpectedly.

Real-World Applications

  • Web Server Management: Manage Node.js web servers, ensuring they stay online and respond to requests.

  • API Management: Deploy and monitor APIs, ensuring stability and high performance.

  • Background Tasks: Automate recurring tasks like data processing or email notifications.

  • Clustered Applications: Scale applications by running multiple instances on different servers.

  • Process Health Monitoring: Track the status of processes, detect failures, and take corrective actions.

Complete Code Implementation Example:

// pm2config.json
{
  "apps": [
    {
      "name": "my-app",
      "script": "server.js",
      "instances": 4,
      "env": {
        "NODE_ENV": "production"
      }
    }
  ]
}
// Start PM2 with configuration
pm2 start pm2config.json

// Monitor process logs
pm2 logs my-app

Process Monitoring with PM2 Enterprise

Process Monitoring with PM2 Enterprise

Pretend you're the boss of a team of workers (processes). As a boss, you want to keep an eye on how well they're doing, fix any problems, and make sure they're all working together smoothly.

PM2 Enterprise is like a super-powered tool that helps you monitor and manage your processes like a boss. It gives you real-time insights into how your processes are performing, lets you troubleshoot issues quickly, and ensures they all work in sync.

Real-Time Monitoring

Imagine having a dashboard where you can see how your processes are doing in real-time. PM2 Enterprise gives you just that. It shows you how much CPU and memory each process is using, how long it's been running, and any errors it's encountered. This helps you spot problems early on and take action before they become major issues.

Code Snippet:

pm2 monitor

Real-Time Events Dashboard

Think of it as a live feed of all the events happening with your processes. PM2 Enterprise has a dashboard that shows you when processes start, stop, crash, or encounter errors. It's like a running commentary of your processes' activities, helping you stay on top of everything.

Code Snippet:

pm2 events

Troubleshooting

When a process misbehaves, it's like a naughty child who needs some discipline. PM2 Enterprise helps you find the cause of the problem quickly. It provides detailed error logs and stack traces, making it easier to identify the exact issue and fix it.

Code Snippet:

pm2 logs -u 10 --nostream

Process Control

As the boss, you have the power to control your processes like a superhero. PM2 Enterprise lets you stop, restart, or scale up/down your processes as needed. It's like having a remote control for your processes, allowing you to manage them from anywhere.

Code Snippet:

pm2 stop <app_name>

Applications in Real World

  • Website Hosting: Monitor and manage multiple websites running on your servers, ensuring they're always up and running.

  • Background Jobs: Keep track of long-running tasks and make sure they don't get stuck or crash.

  • Microservices: Monitor and manage a complex network of interconnected services, ensuring they work together seamlessly.

  • DevOps: Improve development and deployment processes by monitoring and troubleshooting applications in real-time.

  • Customer Support: Quickly identify and resolve issues with customer-facing applications, ensuring a smooth user experience.

Customization

Customization

Changing pm2's behavior

1. Process name

  • By default, pm2 names processes using their script name.

  • You can specify a custom name using the --name flag:

    pm2 start app.js --name my-app

2. Environment variables

  • PM2 process can access environment variables defined in the system.

  • You can set custom environment variables for a process using the --env flag:

    pm2 start app.js --env NODE_ENV=production

3. Restart policy

  • PM2 can restart processes based on various events, such as crashes or changes to the script file.

  • You can customize the restart policy using the --restart-policy flag:

    pm2 start app.js --restart-policy never

Managing process resources

1. Limiting memory usage

  • PM2 can limit the amount of memory a process can use.

  • You can set a memory limit using the --max-memory flag:

    pm2 start app.js --max-memory 512

2. Limiting CPU usage

  • PM2 can limit the amount of CPU time a process can use.

  • You can set a CPU limit using the --max-cpu flag:

    pm2 start app.js --max-cpu 50

Scaling and clustering

1. Scaling

  • PM2 can automatically scale processes based on load.

  • You can enable scaling using the --scale flag:

    pm2 start app.js --scale 4

2. Clustering

  • PM2 can spawn multiple instances of a process, creating a cluster.

  • You can enable clustering using the --cluster flag:

    pm2 start app.js --cluster true

Real-world applications

  • Process isolation: Customizing process names helps isolate processes and track them easily in complex deployments.

  • Environment configuration: Setting custom environment variables allows you to adapt processes to different environments (e.g., production, staging).

  • Resource management: Limiting memory and CPU usage prevents resource overconsumption and ensures system stability.

  • Scaling and clustering: Scaling and clustering enable automatic adjustment of resources based on demand, optimizing performance and cost.

Integration with Other Tools

Integration with Other Tools

Monitoring Tools

  • Prometheus: Collects metrics and stores them in a time-series database.

  • Grafana: Visualizes metrics collected by Prometheus.

Load Balancers

  • Nginx: Distributes HTTP traffic across multiple PM2 instances.

  • Traefik: Similar to Nginx, but more flexible and supports multiple protocols.

API Gateways

  • Kong: Manages and secures APIs, and can integrate with PM2 for load balancing.

  • Zuul: Open-source API gateway that can also be used for load balancing.

Cloud Platforms

  • AWS Elastic Container Service (ECS): Manages and schedules Docker and PM2 containers on AWS.

  • Google Kubernetes Engine (GKE): Manages and schedules Docker and PM2 containers on Google Cloud Platform.

Real-World Applications

Monitoring:

  • Monitor server uptime, CPU usage, memory consumption, and application errors.

  • Use Grafana to create dashboards to visualize metrics and identify performance issues.

Load Balancing:

  • Distribute traffic across multiple servers to handle peak demand.

  • Improve website availability and performance by preventing single points of failure.

API Gateways:

  • Secure and manage public-facing APIs.

  • Throttle requests, enforce rate limits, and authenticate users.

Cloud Platforms:

  • Deploy PM2 applications to the cloud for scalability, reliability, and cost optimization.

  • Easily manage and monitor containers across multiple servers.

Example Code To integrate PM2 with Prometheus, you can use the following code:

const pm2 = require('pm2');

pm2.connect(function(err) {
  if (err) {
    console.error(err);
    process.exit(1);
  }

  pm2.launchBus(function(err, bus) {
    if (err) {
      console.error(err);
      process.exit(1);
    }

    bus.on('process:event', function(event) {
      console.log(event);
    });
  });
});

This code will start PM2 and listen for events on the PM2 message bus. Then, you can use Prometheus to collect metrics from the bus.

Process Containerization

Process Containerization with PM2

PM2 is a process manager that helps you manage and monitor your Node.js applications. It allows you to containerize your processes, which means running them in isolated environments.

Benefits of Process Containerization:

  • Isolation: Prevents processes from interfering with each other.

  • Security: Enhances security by limiting process access to resources.

  • Scalability: Makes it easier to manage and scale applications.

How Process Containerization Works:

PM2 creates a separate namespace for each process container. This means that each container has its own set of resources, such as memory, CPU, and network. Processes within a container cannot access resources outside the container.

How to Containerize Processes with PM2:

  1. Install PM2:

$ npm install pm2 -g

  1. Create a process container:

$ pm2 start process-name --container

  1. Start a process within the container:

$ pm2 start process-name --container

Real-World Applications:

  • Micro-services: Containerizing each micro-service ensures isolation and prevents issues in one service from affecting others.

  • Legacy Applications: Containerizing legacy applications that have dependencies on different versions of libraries or operating systems.

  • Security: Isolating processes that handle sensitive data to prevent unauthorized access.

Code Example:

Containerizing a process:

pm2 start my-app --container
pm2 start my-other-app --container

Starting a process within a container:

pm2 start my-app-process --container process-name
pm2 start my-other-app-process --container process-name

Monitoring Processes:

You can use PM2's dashboard or CLI tools to monitor processes and manage containers. For example, to list all containers:

$ pm2 list --container

Remember:

  • Each container requires its own set of resources, so you'll need to monitor resource consumption.

  • Containers should be designed carefully to avoid over-provisioning or under-provisioning.

  • Containerization is not a replacement for proper application design and architecture.

Process Monitoring with Keymetrics

Process Monitoring with Keymetrics in Node.js using PM2

PM2 is a powerful process manager for Node.js applications. It allows you to monitor and manage your processes, ensuring they run smoothly and efficiently. Keymetrics are specific performance indicators that provide valuable insights into your process's behavior.

Keymetrics:

  • CPU Usage: The percentage of CPU resources utilized by the process.

  • Memory Usage: The amount of memory consumed by the process.

  • Status: The current state of the process (running, stopped, exited, etc.).

  • Uptime: The duration for which the process has been running.

  • Response Time: The time taken by the process to handle requests (if applicable).

Monitoring Keymetrics

To monitor keymetrics using PM2, install the package globally:

npm install pm2 -g

Start your process with PM2 and specify the keymetrics you want to monitor:

pm2 start app.js --name "My App" --watch --metric

The --watch flag keeps the process alive and restarts it if it crashes. The --metric flag enables keymetric monitoring.

Code Implementation

Complete Command:

pm2 start app.js --name "My App" --watch --metrics --watch-delay=5000 --ignore-watch="node_modules/**"

  • --watch-delay=5000: Sets the watch delay to 5 seconds.

  • --ignore-watch="node_modules/**": Ignores watch changes in the node_modules directory.

Real World Applications

  • CPU Usage: Identifying bottlenecks and optimizing resource consumption.

  • Memory Usage: Detecting memory leaks and preventing out-of-memory errors.

  • Status: Monitoring process crashes and ensuring high availability.

  • Uptime: Tracking the stability and reliability of your applications.

  • Response Time: Evaluating the performance of web servers, APIs, and databases.

Process Configuration

Process Configuration in Node.JS PM2

PM2 is a process manager for Node.js applications. It allows you to easily manage and monitor your applications, and to keep them running even if they crash.

Process configuration allows you to customize how PM2 manages your applications. You can configure various settings, such as the number of instances to run, the memory limit, and the restart policy.

Common Configuration Options

name: The name of the application. This is used to identify the application in the PM2 ecosystem.

script: The path to the main script file of the application.

instances: The number of instances of the application to run.

max_memory_restart: The maximum amount of memory that the application can use before PM2 restarts it.

restart_delay: The amount of time to wait before restarting the application after it crashes.

log_file: The path to the log file for the application.

Advanced Configuration Options

env: The environment variables to set for the application.

args: The command-line arguments to pass to the application.

cwd: The working directory for the application.

exec_mode: The execution mode for the application. This can be either "fork" or "cluster".

watch: A list of files or directories to watch for changes. When a file or directory in this list changes, PM2 will restart the application.

Real-World Applications

Process configuration can be used to optimize the performance and reliability of your Node.js applications. For example, you can use process configuration to:

  • Run multiple instances of an application: This can improve the performance of your application by distributing the load across multiple CPUs.

  • Restart an application automatically after a crash: This can prevent your application from becoming unavailable if it crashes.

  • Limit the memory usage of an application: This can prevent your application from using too much memory and causing performance problems.

  • Set environment variables for an application: This can allow you to pass configuration settings to your application without having to hard-code them into the script file.

Code Example

The following code example shows how to configure a PM2 process:

const pm2 = require('pm2');

pm2.start({
  name: 'my-app',
  script: 'index.js',
  instances: 4,
  max_memory_restart: '512M',
  restart_delay: '5s',
  log_file: 'my-app.log',
});

This code will start a PM2 process with the following configuration:

  • Name: "my-app"

  • Script: "index.js"

  • Instances: 4

  • Max memory restart: 512MB

  • Restart delay: 5 seconds

  • Log file: "my-app.log"

Process Management

Process Management

Managing processes is a key aspect of any server-side application, especially in larger systems with many interconnected services. PM2 is a process manager for Node.js applications that makes it easy to manage and monitor them. It provides a number of features, including:

1. Process Launching and Management

PM2 allows you to easily start, stop, and restart your Node.js applications. You can also manage multiple instances of your application simultaneously, which is useful for load balancing and high availability.

2. Process Monitoring

PM2 provides real-time monitoring of your processes, including CPU usage, memory usage, and event loop latency. This information can help you identify potential performance issues and troubleshoot any problems.

3. Process Logging

PM2 automatically logs all output from your processes, including stdout, stderr, and crash reports. This can be useful for debugging and auditing purposes.

4. Process Scaling

PM2 can automatically scale your processes up or down based on demand. This can help you ensure that your application is always running at the optimal level of performance.

5. Process Clustering

PM2 can create clusters of your processes, which can improve performance and reliability. A cluster is a group of processes that share the same code and data, but run independently. This can help to isolate errors and prevent a single process failure from affecting the entire cluster.

Real-World Examples

Some real-world examples of how PM2 can be used include:

  • Managing a web server that handles a high volume of traffic

  • Deploying a microservices architecture

  • Automating the deployment and management of a Node.js application

Getting Started with PM2

To get started with PM2, you can install it using the following command:

npm install -g pm2

Once PM2 is installed, you can start managing your processes by running the following command:

pm2 start index.js

This will start your Node.js application and create a process manager for it. You can then use the pm2 command to manage your process, such as:

pm2 stop index.js
pm2 restart index.js
pm2 monit

For more information on PM2, please refer to the official documentation: https://pm2.io/doc/en/

Process Scaling

Process Scaling Explained

Imagine you have a website that gets a lot of traffic, like a popular online store. As more and more people visit your site, you need more power to handle all the visitors and keep your site running smoothly. That's where process scaling comes in. It's like adding more engines to a car to make it go faster.

Horizontal Scaling

Horizontal scaling is when you add more servers to your system to handle the increased load. It's like adding more lanes to a highway to reduce traffic. You can add as many servers as you need to until the traffic is manageable again.

pm2 start app.js -i 4

In this command, -i 4 specifies that you want to start 4 instances of your app.

Vertical Scaling

Vertical scaling is when you upgrade your existing servers to handle more load. It's like upgrading the engine in your car to make it more powerful. You can upgrade your servers' RAM, CPU, or storage to improve their performance.

pm2 scale app 2

In this command, app is the name of your application and 2 specifies that you want to scale it to 2 instances.

Load Balancing

Load balancing is a way to distribute traffic across multiple servers. It ensures that each server is handling an equal amount of load, preventing any one server from becoming overwhelmed. Think of it like having multiple doors to a building, each leading to the same destination. Traffic gets divided evenly among the doors, so no one door gets too crowded.

pm2 cluster

This command creates a cluster of your application, which means it will automatically use load balancing.

Real-world Applications

Here are some real-world applications of process scaling:

  • E-commerce websites: During peak shopping times, websites can scale up to handle the increased traffic and ensure that customers can make purchases without experiencing delays.

  • Streaming services: To ensure that you can always watch your favorite shows and movies without buffering, streaming services scale their servers based on the number of people watching content at a given time.

  • Databases: Databases can scale horizontally or vertically to handle the growing amount of data generated by modern applications.

Process Clustering

Process Clustering

What is Process Clustering?

Imagine you have a bakery. Baking one loaf of bread takes time. If you want to bake more bread faster, you can hire more bakers. In the same way, process clustering allows you to run multiple copies of your Node.js application on a single server, just like having more bakers to bake more bread.

Types of Process Clustering

  • Fork Clustering: Creates separate processes for each instance of your application. Think of it like having each baker working on his own oven.

  • Cluster Mode: Uses a single Node.js instance to run multiple workers. Think of it like having all the bakers working in the same oven, but taking turns.

Benefits of Process Clustering

  • Increased performance: Multiple processes can handle more requests simultaneously, speeding up your application.

  • Fault tolerance: If one process fails, the others keep running, ensuring availability.

  • Scalability: You can easily add or remove processes as needed, adjusting your capacity to meet demand.

Real-World Applications

  • Web applications: Handle a high volume of user requests.

  • Background tasks: Run time-consuming jobs without blocking your main application.

  • Data processing: Process large datasets efficiently.

Code Implementation for Fork Clustering

const pm2 = require('pm2');

const instances = 4; // Number of processes to cluster

pm2.start({
  script: 'index.js', // Path to your application's main script
  instances,
  env: {
    NODE_ENV: 'clustered' // Custom environment variable to indicate clustered mode
  }
});

Code Implementation for Cluster Mode

const cluster = require('cluster');
const numCPUs = require('os').cpus().length;

if (cluster.isMaster) {
  // Master process
  for (let i = 0; i < numCPUs; i++) {
    cluster.fork(); // Create a worker
  }
} else {
  // Worker process
  require('./index.js'); // Run your application's main script
}

PM2 API

PM2 API for Node.js

Overview

PM2 is a process manager for Node.js applications. It allows you to manage and monitor your applications easily. The PM2 API provides a way to interact with PM2 programmatically.

Topics

1. Starting and Stopping Applications

  • start(name, scriptPath): Starts an application.

  • stop(name): Stops an application.

  • restart(name): Restarts an application.

Example:

const pm2 = require('pm2');

pm2.start('my-app', {
  name: 'My App',
  script: 'index.js',
});

pm2.stop('my-app');

Potential Applications:

  • Automating application deployments and restarts.

  • Monitoring application status and responding to changes.

2. Listing Applications

  • list(): Lists all running applications.

  • list(options): Customizes the list output (e.g., filter by name, status).

Example:

pm2.list(function(err, apps) {
  console.log(apps);
});

Potential Applications:

  • Displaying a list of running applications for debugging or monitoring purposes.

  • Identifying applications that are not running correctly.

3. Logging

  • getLog(name, options): Gets the logs for an application.

  • deleteLog(name): Deletes the logs for an application.

Example:

pm2.getLog('my-app', function(err, log) {
  console.log(log);
});

Potential Applications:

  • Debugging application issues by examining logs.

  • Monitoring application activity and performance.

4. Configuration

  • reload(options): Reloads the PM2 configuration file.

  • getConfig(): Gets the current PM2 configuration.

Example:

pm2.getConfig((err, config) => {
  console.log(config);
});

Potential Applications:

  • Modifying PM2 settings dynamically to adapt to changing system requirements or application needs.

5. Other Actions

  • connect(): Connects to the PM2 daemon.

  • disconnect(): Disconnects from the PM2 daemon.

  • delete(name): Deletes an application.

  • flush(): Deletes all PM2 applications.

Example:

pm2.delete('my-app', function(err) {
  if (err) {
    console.error(err);
  }
});

Potential Applications:

  • Removing applications that are no longer needed.

  • Cleaning up the PM2 installation after uninstalling.

Process Monitoring with PM2 Plus

Process Monitoring with PM2 Plus

Monitoring Processes

PM2 Plus allows you to monitor the health and performance of your Node.js applications in real-time. You can:

  • Check process status (running, stopped, restarted)

  • View CPU and memory usage

  • Track response times and error logs

  • Get alerts for errors and performance issues

Real-world Example:

A web application may use PM2 to monitor the server process. It can detect any issues and automatically restart the server, ensuring that the application remains accessible to users.

Code Snippet:

// Create a PM2 instance
const pm2 = require('pm2');

// Start monitoring a process
pm2.start({
  script: './index.js',
  name: 'my-app',
  watch: true
});

// Get process status
pm2.status('my-app', (err, process) => {
  if (process.pm2_env.status === 'online') {
    console.log('Process is running.');
  } else {
    console.log('Process is not running.');
  }
});

Log Monitoring

PM2 Plus can also monitor application logs for errors and performance issues. You can:

  • View logs in real-time

  • Filter logs by level (error, warning, info)

  • Search for specific keywords or phrases

Real-world Example:

A customer relationship management (CRM) system may use PM2 to monitor its logs. It can detect any errors that affect customer interactions and notify the support team for quick resolution.

Code Snippet:

// Get application logs
pm2.logs('my-app', (err, logs) => {
  logs.forEach(log => {
    console.log(log.date, log.level, log.msg);
  });
});

Custom Metrics Monitoring

PM2 Plus allows you to monitor custom metrics, such as request count, database connection count, or API response times. This enables you to track key performance indicators (KPIs) and optimize your application accordingly.

Real-world Example:

An e-commerce website may use PM2 to monitor the number of successful transactions per hour. By tracking this metric, the website can identify peak traffic times and adjust its infrastructure to handle the load.

Code Snippet:

// Create a custom metric
pm2.addMetric({
  name: 'successful_transactions',
  unit: 'count'
});

// Increase the metric value
pm2.incMetric('successful_transactions', 1);

Clustering and Load Balancing

PM2 Plus supports clustering and load balancing. This allows you to distribute your application across multiple machines, ensuring high availability and scalability.

Real-world Example:

A high-traffic website may use PM2 to cluster its application. This will allow it to handle a larger number of users simultaneously and reduce the risk of downtime.

Code Snippet:

// Create a cluster
pm2.cluster('my-app', {
  instances: 4
});

// Enable load balancing
pm2.enableLB('my-app');

Process Script Execution

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Process Logs

Process Logs

Imagine your server as a car engine, and the logs are like the car's dashboard. They tell you what's happening under the hood, including errors, warnings, and other important information.

Types of Logs

There are two main types of logs:

  • stdout (standard output): Shows the output of your application's code.

  • stderr (standard error): Shows error messages and other important information.

Viewing Logs

To view the logs, you can use a command-line tool like pm2 logs. This command will show you the logs for all your running applications.

pm2 logs

You can also view logs using a third-party service like Papertrail or Graylog. These services allow you to store and search your logs centrally.

Real-World Applications

Logs are essential for troubleshooting and debugging problems. They can help you identify issues in your code, track down performance bottlenecks, and detect security breaches.

For example, let's say your website is not loading properly. You can use the logs to check if there are any errors or warnings that might be causing the problem.

Code Example

Here's a simple Node.js script that generates some logs:

console.log('Hello world!'); // stdout
console.error('An error occurred!'); // stderr

You can then view the logs using the pm2 logs command:

pm2 logs my-app

Improved Code Example

You can use the pm2-logrotate module to automatically rotate your logs:

const pm2 = require('pm2');

pm2.connect(function(err) {
  if (err) return;

  pm2.start({
    script: 'index.js',
    name: 'my-app',
    logrotate: {
      max_size: 10 * 1024 * 1024, // 10MB
      keep: 5 // Keep the last 5 log files
    }
  }, function(err) {
    if (err) return;

    console.log('App started');
  });
});

PM2 Release Notes

Topic 1: Cluster Mode

What is it?

Cluster mode allows you to run multiple copies of your application on different servers or CPUs. This can improve performance and reliability.

How does it work?

PM2 will automatically create and manage multiple processes for your application. These processes will share the same code and data, but will run independently.

Code example:

// start a cluster of 4 processes
pm2 start app.js -i 4

Potential applications:

  • Scaling up your application to handle more traffic

  • Improving reliability by having multiple copies of your application running

  • Balancing load across multiple servers or CPUs

Topic 2: Zero-Downtime Deployments

What is it?

Zero-downtime deployments allow you to update your application without interrupting service to your users.

How does it work?

PM2 will create a new copy of your application with the updated code. Then, it will gradually switch traffic from the old copy to the new copy. This ensures that your users never experience any downtime.

Code example:

// deploy a new version of your application
pm2 deploy app.js

Potential applications:

  • Rolling out new features or bug fixes without disrupting service

  • Maintaining uptime for critical applications

  • Reducing downtime during software updates

Topic 3: Monitoring and Analytics

What is it?

PM2 provides a built-in dashboard and API for monitoring the performance and health of your application.

How does it work?

PM2 collects metrics such as CPU usage, memory usage, and response times. You can view these metrics in the dashboard or access them through the API.

Code example:

// get the monitoring data for your application
const monitoringData = pm2.getMonitoringData();

// print the CPU usage
console.log(monitoringData.cpu);

Potential applications:

  • Troubleshooting performance issues

  • Identifying bottlenecks in your application

  • Tracking the health of your application over time

Topic 4: Auto-Restart and Recovery

What is it?

PM2 can automatically restart your application if it crashes or becomes unresponsive. This ensures that your application always stays up and running.

How does it work?

PM2 monitors the health of your application. If it detects that your application has crashed, it will automatically restart it.

Code example:

// enable auto-restart for your application
pm2 start app.js --watch

Potential applications:

  • Ensuring that your application is always available

  • Minimizing downtime due to crashes or errors

  • Improving reliability and stability

Topic 5: Logs and Metrics

What is it?

PM2 can collect and store logs and metrics from your application. This information can be used for troubleshooting, debugging, and performance analysis.

How does it work?

PM2 can automatically log all output from your application. You can also configure PM2 to collect custom metrics.

Code example:

// enable logging for your application
pm2 start app.js --log

Potential applications:

  • Debugging errors and identifying issues

  • Tracking the performance of your application

  • Generating reports on application usage

Process Log Rotation

Process Log Rotation in PM2

Imagine a log file as a giant notebook that records everything a running program does. But as the notebook fills up, it becomes harder to read and find what you need. Log rotation is like using a fresh notebook every day, making it easier to keep track of what's happening.

How Log Rotation Works:

  1. Set a Size Limit: Choose the maximum size of the log file (e.g., 10 MB).

  2. Daily Rotation: Every day, a new log file is created and the old one is compressed and renamed.

  3. Kept Log Files: You can choose how many log files to keep before deleting older ones (e.g., keep 5).

Code Implementation:

Add the following line to your PM2 config file (e.g., ecosystem.config.js):

module.exports = {
  apps: [
    {
      name: "myapp",
      log_date_format: "YYYY-MM-DD",
      max_log_size: "10M",
      max_old_space_size: "256",
      out_file: "logs/myapp.out.log",
      error_file: "logs/myapp.err.log",
      log_file: "logs/myapp.combined.log",
    },
  ],
};

  • log_date_format: Customizes the date format in the log file.

  • max_log_size: Sets the maximum size of the log file.

  • max_old_space_size: Limits the amount of memory used for old console output.

  • out_file: Specifies the file to log stdout (standard output) messages.

  • error_file: Specifies the file to log stderr (error) messages.

  • log_file: Specifies the file to log both stdout and stderr messages (combined log).

Real-World Use Cases:

  • Debugging: Easier to find errors and issues in specific time periods.

  • Troubleshooting: When a problem occurs, you can quickly access detailed logs from a specific day.

  • Security Audits: Keep a chronological record of all program activities for auditing purposes.

Contributing to PM2

Understanding PM2's Contribution Guidelines

PM2 is a toolkit for managing and monitoring Node.js applications. It allows you to start, stop, restart, and scale your Node.js applications easily.

To contribute to PM2, you follow these guidelines:

1. Find an Issue or Feature to Work On

  • Browse the PM2 GitHub repository (https://github.com/Unitech/pm2/issues) to find existing issues or feature requests that align with your interests.

  • If you have an idea for a new feature or improvement, you can create a new issue and describe your proposal.

2. Create a Pull Request

  • Fork the PM2 repository to your local machine.

  • Make your changes in a new branch and keep them aligned with the guidelines (e.g., coding style, testing).

  • Create a pull request (PR) and describe what you've changed and why.

3. Get Feedback and Iterate

  • After submitting your PR, PM2 maintainers will review your changes and provide feedback.

  • You may need to make revisions or address any concerns raised.

  • Collaborate with the maintainers to refine your contribution.

4. Testing and Approval

  • Once your changes have been reviewed and approved, they will be merged into the PM2 repository.

  • The merged changes will be tested and released in the next PM2 version.

Real-World Applications of PM2

PM2 has numerous applications in the real world:

  • Production Environments: Deploying and managing Node.js applications in production environments.

  • Continuous Integration/Continuous Delivery (CI/CD): Automating application building, testing, and deployment.

  • Load Balancing: Distributing application requests across multiple instances for better performance.

  • Log Monitoring: Centralizing and monitoring application logs for debugging and troubleshooting.

Example Code Implementation

To start a Node.js application using PM2:

pm2 start index.js

To monitor the running application:

pm2 monit

To list all running applications:

pm2 ls

Conclusion

Contributing to PM2 involves understanding the guidelines, creating and reviewing pull requests, and receiving feedback from maintainers. PM2 offers valuable tools for managing Node.js applications in various real-world scenarios, such as production environments, CI/CD, and load balancing.

Log Management

Log Management

Logs are messages that are generated by your application as it runs. They can be useful for debugging, troubleshooting, and monitoring the health of your application.

Types of Logs

  • Standard output (stdout): Logs that are printed to the console by your application.

  • Standard error (stderr): Logs that are printed to the console when an error occurs.

  • Custom logs: Logs that are generated by your application using the console.log() function.

PM2 Log Management

PM2 provides a number of features for managing logs, including:

  • Log rotation: Automatically rotates and archives logs to prevent them from filling up your disk space.

  • Log levels: Allows you to control the level of detail of logs that are generated.

  • Log filtering: Allows you to filter logs by level, type, or keyword.

  • Log aggregation: Aggregates logs from multiple processes into a single location.

How to Configure Log Management

You can configure log management in PM2 by setting the logging property in your PM2 configuration file (pm2.config.js):

module.exports = {
  logging: {
    level: "info",
    rotate: {
      interval: "1d",
      maxSize: "10m",
    },
    filter: "error",
    aggregate: {
      disable: true,
    },
  },
};

Potential Applications

  • Debugging: Logs can be used to identify and fix errors in your application.

  • Troubleshooting: Logs can be used to track down the cause of problems with your application.

  • Monitoring: Logs can be used to monitor the health of your application and identify potential issues.

  • Analytics: Logs can be used to collect data about the usage of your application.

Real-World Examples

Here is an example of how you can use PM2 to manage logs for a Node.js application:

const pm2 = require("pm2");

pm2.start({
  script: "./app.js",
  logging: {
    level: "debug",
    rotate: {
      interval: "1d",
      maxSize: "10m",
    },
    filter: "error",
  },
});

This will start the application in debug mode and rotate the logs every day. Logs will be filtered to only include errors.

Startup Script Generation

Startup Script Generation with PM2

PM2 is a process manager for Node.js applications that allows you to easily manage and monitor your processes. One of the features of PM2 is the ability to generate startup scripts, which are scripts that can be used to start your application as a service on Linux or macOS.

Creating a Startup Script

To create a startup script, you can use the pm2 startup command. This command will generate a script that contains the following information:

  • The name of your application

  • The command to start your application

  • The arguments to pass to your application

  • The environment variables to set for your application

The following code snippet shows an example of a startup script generated by pm2 startup:

#!/bin/bash

# Name of the application
NAME=my-app

# Command to start the application
CMD=node index.js

# Arguments to pass to the application
ARGS=""

# Environment variables to set for the application
ENV_VARS=""

# Start the application
exec pm2 start $NAME --name $NAME -- $CMD $ARGS --env $ENV_VARS

Using a Startup Script

Once you have created a startup script, you can use it to start your application as a service. To do this, you can follow these steps:

  1. Copy the startup script to the /etc/init.d directory on Linux or the /Library/LaunchDaemons directory on macOS.

  2. Make sure the startup script is executable by running the following command:

chmod +x /etc/init.d/$NAME

  1. Start the application as a service by running the following command:

service $NAME start

Potential Applications

Startup scripts can be used in a variety of real-world applications, such as:

  • Starting a web server.

  • Starting a database server.

  • Starting a background process.

  • Monitoring a process for failures.

Improved Examples

The following is an improved example of a startup script that starts a web server:

#!/bin/bash

# Name of the application
NAME=my-web-server

# Command to start the application
CMD=node index.js

# Arguments to pass to the application
ARGS=""

# Environment variables to set for the application
ENV_VARS=""

# Start the application
exec pm2 start $NAME --name $NAME -- $CMD $ARGS --env $ENV_VARS

# Ensure the application restarts on failure
exec pm2 monit

This script will start the web server and monitor it for failures. If the web server fails, PM2 will automatically restart it.

Process Zero Downtime Reload

Zero Downtime Reload

What is it?

Imagine you have a website or app that needs to be updated. With regular methods, you'd have to temporarily shut it down to make the changes. This would cause downtime and possibly lose users.

Zero Downtime Reload allows you to make updates to your code without interrupting service to your users. It's like changing the tires on a moving car!

How does it work?

  1. Start two instances: PM2 lets you run multiple instances of your app simultaneously. So, you start a backup instance (PM2 calls it an "ecosystem").

  2. Update the backup: You make the changes to your code in the backup instance.

  3. Redirect traffic: PM2 smoothly redirects users' requests from the old instance to the updated backup instance.

  4. Stop the old instance: Once the update is complete, PM2 stops the old instance.

Benefits:

  • No downtime for your users

  • Fast and efficient updates

  • Rollback option if the update causes issues

Real-World Examples:

  • E-commerce websites: Update product details, promotions, or payment gateways without interrupting shopping.

  • Social media apps: Introduce new features or fix bugs without interrupting user interactions.

  • Banking platforms: Make security updates or introduce new services without disrupting financial transactions.

Code Implementation:

// Start the main instance
pm2 start main.js

// Start the backup instance
pm2 start backup.js --watch

// Update the backup instance
// (Edit backup.js and save the changes)

// Redirect traffic to the backup
pm2 reload ecosystem

// Stop the main instance
pm2 stop main

Potential Applications:

Zero Downtime Reload is essential for any application that requires continuous availability, such as:

  • Mission-critical systems

  • High-traffic websites

  • Real-time communication apps

  • Data processing pipelines

Environment Management

Simplified Explanation of PM2 Environment Management

PM2, a Node.js process manager, allows you to manage multiple Node.js applications on a single server. Environment management in PM2 refers to configuring and managing the environment variables available to your applications.

Understanding Environment Variables

Environment variables are like labels that store information used by your applications. They can contain settings like database passwords, server addresses, or feature flags.

Loading Environment Variables

PM2 can load environment variables from multiple sources:

  • Process.env: The default environment object in Node.js.

  • .env file: A file in the root directory of your application that contains environment variables in the format KEY=VALUE.

  • PM2 Environment: Variables set explicitly using PM2 commands.

Setting Environment Variables Programmatically

You can set environment variables programmatically using the following syntax:

pm2 set env VARIABLE_NAME VALUE

For example, to set a database password:

pm2 set env DB_PASSWORD my_secret_password

Accessing Environment Variables

You can access environment variables in your Node.js application like this:

console.log(process.env.VARIABLE_NAME);

Real-World Applications

  • Managing configuration settings for different environments (e.g., development, production)

  • Storing sensitive information like passwords and tokens securely

  • Enabling feature flags to control application behavior on demand

Complete Code Implementation Example

Suppose you have a Node.js application that connects to a database. You can load your database credentials from a .env file:

# .env file
DB_HOST=localhost
DB_USER=admin
DB_PASSWORD=my_secret_password

Then, in your application, you can access the credentials like this:

// app.js
const host = process.env.DB_HOST;
const user = process.env.DB_USER;
const password = process.env.DB_PASSWORD;
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