Is it possible to run multiple Nightmare instances in parallel?

Yes, it is possible to run multiple Nightmare instances in parallel. Nightmare is an automation library for Node.js that enables you to automate tasks in Electron, which is essentially a headless browser, though it can also run with a GUI.

To run multiple instances in parallel, you will need to manage these instances either by launching multiple Node.js processes or by handling concurrency within a single Node.js process using async programming techniques like Promises or async/await.

Below is an example of how you might run multiple Nightmare instances in parallel using Promise.all in Node.js:

const Nightmare = require('nightmare');

const runInstance = async (url) => {
  const nightmare = Nightmare();
  try {
    const title = await nightmare
      .goto(url)
      .wait('body')
      .evaluate(() => document.title)
      .end();
    console.log(`Title of ${url}:`, title);
    return title;
  } catch (error) {
    console.error(`Error for ${url}:`, error);
  }
};

const urls = [
  'http://example.com',
  'http://example.org',
  'http://example.net',
  // Add more URLs as needed
];

const startScraping = async () => {
  try {
    const results = await Promise.all(urls.map(runInstance));
    console.log('All instances finished:', results);
  } catch (error) {
    console.error('An error occurred:', error);
  }
};

startScraping();

In the example above, Promise.all runs each Nightmare instance created in the runInstance function concurrently. Note that using Promise.all will cause all promises to reject if any single promise rejects. If you want to allow other instances to continue even if one fails, you might consider using Promise.allSettled instead.

However, it's important to understand the limitations and be aware of the system's resources. Running too many instances in parallel can overwhelm your system's memory and CPU, causing the entire process to slow down or even crash.

If you need to scale up significantly, you might consider using a job queue and running each job in a separate process or using a cluster of machines. Tools like PM2 can help with managing multiple processes in Node.js.

Lastly, ensure you're following ethical web scraping practices and the terms of service of the websites you're scraping. Overloading a server with too many concurrent requests can be seen as a denial-of-service attack and may be illegal or result in being blocked from the website.