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Solution of running crash caused by node error

2022-07-04 07:01:00 【Brother Lei talks about programming】

Many people have such an image ,NodeJS Faster ; But because it's single threaded , So it's unstable , It's not safe , Not suitable for complex business ; It's more suitable for high concurrency requirements , And simple business scenarios .

stay Express The author of TJ Holowaychuk Of a farewell Node.js The following counts are listed in the article ：

Farewell NodeJS (TJ Holowaychuk)

• you may get duplicate callbacks

• you may not get a callback at all (lost in limbo)

• you may get out-of-band errors

• emitters may get multiple “error” events

• missing “error” events sends everything to hell

• often unsure what requires “error” handlers

• “error” handlers are very verbose

• callbacks suck

In fact, these points mainly make two noises ： node.js Error handling is bullshit ,node.js The callback of is also bullshit .

In fact? ？

in fact NodeJS Mileage does exist “ fragile ” One side , Somewhere in a single thread “ Unprocessed ” Exceptions do cause the whole Node.JS Crash exit , Take an example , Here's one node-error.js The file of ：

       
        var http = require('http');
        

        
var server = http.createServer(function (req, res) {
        

        
  // There's a mistake here ,params  yes  undefined
        
  var ok = req.params.ok;
        

        
  res.writeHead(200, {'Content-Type': 'text/plain'});
        
  res.end('Hello World\n');
        
});
        

        
server.listen(8080, '127.0.0.1');
        

        
console.log('Server running at http://127.0.0.1:8080/');
       
       
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Start the service , And test it in the address bar and find http://127.0.0.1:8080/ It is as expected ,node collapsed

       
        $ node node-error
        
Server running at http://127.0.0.1:8080/
        

        
c:\github\script\node-error.js:5
        
  var ok = req.params.ok;
        
                     ^
        
TypeError: Cannot read property 'ok' of undefined
        
    at Server.<anonymous> (c:\github\script\node-error.js:5:22)
        
    at Server.EventEmitter.emit (events.js:98:17)
        
    at HTTPParser.parser.onIncoming (http.js:2108:12)
        
    at HTTPParser.parserOnHeadersComplete [as onHeadersComplete] (http.js:121:23)
        
    at Socket.socket.ondata (http.js:1966:22)
        
    at TCP.onread (net.js:525:27)
       
       
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How to solve it ？

Actually Node.JS To this day , If you can't even solve this problem , It is estimated that no one has used it for a long time .

Use uncaughtException

We can uncaughtException To capture the UN captured data globally Error, At the same time, you can print out the call stack of this function , After capture, it can effectively prevent node Process exits , Such as ：

       
        process.on('uncaughtException', function (err) {
        
  // Print out the error 
        
  console.log(err);
        
  // Print out the wrong call stack for debugging 
        
  console.log(err.stack);
        
});
       
       
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This is equivalent to node Guard inside the process , But this method is not advocated by many people , It means that you can't fully control Node.JS It's abnormal .

Use try/catch

We can also add try/catch, Also ensure thread safety .

       
        var http = require('http');
        

        
http.createServer(function(req, res) {
        
  try {
        
    handler(req, res);
        
  } catch(e) {
        
    console.log('\r\n', e, '\r\n', e.stack);
        
    try {
        
      res.end(e.stack);
        
    } catch(e) { }
        
  }
        
}).listen(8080, '127.0.0.1');
        

        
console.log('Server running at http://127.0.0.1:8080/');
        

        
var handler = function (req, res) {
        
  //Error Popuped
        
  var name = req.params.name;
        

        
  res.writeHead(200, {'Content-Type': 'text/plain'});
        
  res.end('Hello ' + name);
        
};
       
       
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The advantage of this scheme is , You can output the error and call stack directly to the current web page .

Integrate into the framework

The standard HTTP Response processing goes through a series of Middleware（HttpModule）, Finally arrive at Handler, As shown in the figure below ：

Node Solutions to run crashes caused by errors _ Boot up

this some Middleware and Handler stay NodeJS There is a feature in , They're all callback functions , The callback function is the only one that makes Node Where the runtime crashes . According to this characteristic , We only need to integrate one place in the framework try/catch It can solve abnormal problems relatively perfectly , And it will not affect the requests of other users request.

As a matter of fact, now NodeJS WEB Almost all frameworks do this , Such as OurJS Open source blog Based on the WebSvr

There is such an exception handling code ：

       
        try {
        
    handler(req, res);
        
  } catch(err) {
        
    var errorMsg
        
      = '\n'
        
      + 'Error ' + new Date().toISOString() + ' ' + req.url
        
      + '\n'
        
      + err.stack || err.message || 'unknow error'
        
      + '\n'
        
      ;
        

        
    console.error(errorMsg);
        
    Settings.showError
        
      ? res.end('<pre>' + errorMsg + '</pre>')
        
      : res.end();
        
  }
       
       
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1.

So what about the errors not generated in the callback ？ Don't worry about , In fact, this is node The program doesn't work at all .

Besides node Self contained cluster It also has certain fault tolerance , It goes with nginx Of worker Is very similar , But it consumes resources （ Memory ） Slightly larger , Programming is not very convenient ,OurJS This design is not adopted .

guardian NodeJS Process and log errors

present It has been basically solved Node.JS The problem of collapse due to abnormality , But no platform is 100% reliable , There are also some mistakes from Node Thrown by the bottom , There's something unusual try/catch and uncaughtException Can't capture . It was running before ourjs When , Occasionally, I will encounter the file stream reading exception thrown by the bottom , This is a bottom layer libuv Of BUG,node.js stay 0.10.21 It's been fixed in .

In the face of this situation , We should work for nodejs Apply add daemon , Give Way NodeJS It can be revived immediately after encountering abnormal collapse .

in addition , These generated exceptions should also be recorded in the log , And let the exception never happen again .

Use node To guard node

node-forever It provides guard functions and LOG Logging function .

Installation is very easy

       
        [sudo] npm install forever
       
       
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It's also easy to use

       
        $ forever start simple-server.js
        
$ forever list
        
  [0] simple-server.js [ 24597, 24596 ]
       
       
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You can also read the log

       
        forever -o out.log -e err.log my-script.js
       
       
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Use shell Start script daemon node

Use node To guard, the resource cost may be a little high , And it will be slightly complicated ,OurJS Start the script directly at startup to guard the process thread .

If in debian Placed in ourjs Boot file ： /etc/init.d/ourjs

This file is very simple , Only startup options , The core function of guard is an infinite loop while true; To achieve , In order to prevent too dense error blocking process , Interval after each error 1 Restart the service in seconds

       
        WEB_DIR='/var/www/ourjs'
        
WEB_APP='svr/ourjs.js'
        

        
#location of node you want to use
        
NODE_EXE=/root/local/bin/node
        

        
while true; do
        
    {
        
        $NODE_EXE $WEB_DIR/$WEB_APP config.magazine.js
        
        echo "Stopped unexpected, restarting \r\n\r\n"
        
    } 2>> $WEB_DIR/error.log
        
    sleep 1
        
done
       
       
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Error logging is also very simple , Directly output the errors in this process console to error.log File can ： 2>> $WEB_DIR/error.log This business , 2 representative Error.

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Node Solutions to run crashes caused by errors _node.js_02