无法使用pm2启动节点进程

Question

I'm new to node.js and having difficulty to demonize this app using pm2. The app works fine when I go to /srv/myapp and run yarn start but when I try to demonize it by going to /srv/myapp and run pm2 start index.js

I see that the process seem to have started:

[PM2] Starting /srv/myapp/index.js in fork_mode (1 instance)
[PM2] Done.
┌──────────┬────┬──────┬───────┬────────┬─────────┬────────┬─────┬───────────┬──────┬──────────┐
│ App name │ id │ mode │ pid   │ status │ restart │ uptime │ cpu │ mem       │ user │ watching │
├──────────┼────┼──────┼───────┼────────┼─────────┼────────┼─────┼───────────┼──────┼──────────┤
│ index    │ 0  │ fork │ 14528 │ online │ 0       │ 0s     │ 0%  │ 16.0 MB   │ root │ disabled │
└──────────┴────┴──────┴───────┴────────┴─────────┴────────┴─────┴───────────┴──────┴──────────┘
 Use `pm2 show <id|name>` to get more details about an app

But the front end does not respond (instead I get 502 errors and the node server does not listen on port 3000 as expected ( fuser 3000/tcp returns no results).

What could be wrong here? How can I fix it?

Answer 1

通过命令检查pm2日志： pm2 logs如果没有错误，则说明您的应用程序没有问题。

Answer 2

pm2 starts your app with node, one problem is it doesn't provide any logging or output like starting an app by other means (such as node index.js does), so it doesn't really let you know if there is anything going wrong.

I've always found it's a good idea to test your app by starting it with node before pm2 .

Given node index.js causes the error: import bb from 'bluebird';SyntaxError: Unexpected token import , which makes it sound like you're using ES6 import feature, not supported by Node by default . I suspect Yarn is either enabling these features, or transpiling your ES6 code to ES5 for Node to run when you do the yard start , but I'm not familiar with Yarn to know.

It may be you're pointing at the wrong file, and there's a transpiled file dist.js (as an example) already created that Yarn is happily running with the opaque start command.

---

Edit: After looking at the source, it looks to be using something called babel-node . See the start script in the package.json :

"scripts": {
  "start": "babel-node index.js",

pm2 doesn't know to run your index.js with this babel-node thing, and even if it did babel-node strongly recommends you do not use babel-node in production (which presumably you are doing with pm2 ):

Not meant for production use You should not be using babel-node in production. It is unnecessarily heavy, with high memory usage due to the cache being stored in memory. You will also always experience a startup performance penalty as the entire app needs to be compiled on the fly.

Check out the example Node.js server with Babel for an idea of how to use Babel in a production deployment.

And there's also a note about ES6 module loading:

ES6-style module-loading may not function as expected Due to technical limitations ES6-style module-loading is not fully supported in >a babel-node REPL.

I'd strongly recommend you add a build script to produce a 'distribution' transpiled version with babel and deploy that!

"scripts": {
  "start": "babel-node index.js",
  "build": "babel index.js --out-file index-dist.js

Or something along those lines, and run yarn build (or yarn run build ?) then pm2 start index-dist.js .