logging multiple instances

[rlidwka]

1. When pm2 starts N instances, it outputs all errors from them to one logfile
2. When pm2 tails these logs to stdout, it reads this logfile N times (one time per instance)

So, pm2 logs shows every line of every instance N times where N is an amount of instances.

$ cat test.js
setInterval(function() {
        console.error(process.pid);
}, 10000);

$ pm2 start test.js -i 4
⌬ PM2 Configuration :  { script: 'test.js', name: 'test', instances: '4' }
⌬ PM2 You can write the current configuration by adding -w option
⌬ PM2 Process launched
┌─────────┬────┬───────┬────────┬───────────┬──────────┬───────────────────────────────────┐
│ Script  │ id │ PID   │ status │ Restarted │ memory   │ err logs                          │
├─────────┼────┼───────┼────────┼───────────┼──────────┼───────────────────────────────────┤
│ test.js │ 3  │ 19527 │ online │ 0         │ 8.637 MB │ /home/alex/.pm2/logs/test-err.log │
├─────────┼────┼───────┼────────┼───────────┼──────────┼───────────────────────────────────┤
│ test.js │ 2  │ 19521 │ online │ 0         │ 8.637 MB │ /home/alex/.pm2/logs/test-err.log │
├─────────┼────┼───────┼────────┼───────────┼──────────┼───────────────────────────────────┤
│ test.js │ 1  │ 19515 │ online │ 0         │ 8.641 MB │ /home/alex/.pm2/logs/test-err.log │
├─────────┼────┼───────┼────────┼───────────┼──────────┼───────────────────────────────────┤
│ test.js │ 0  │ 19513 │ online │ 0         │ 8.637 MB │ /home/alex/.pm2/logs/test-err.log │
└─────────┴────┴───────┴────────┴───────────┴──────────┴───────────────────────────────────┘

$ pm2 logs
[test err (l269)] 19515
[test err (l269)] 19515 <-- duplicate
[test err (l269)] 19515 <-- duplicate
[test err (l269)] 19515 <-- duplicate
[test err (l270)] 19521
[test err (l270)] 19521 <-- duplicate
[test err (l270)] 19521 <-- duplicate
[test err (l270)] 19521 <-- duplicate
[test err (l271)] 19527
[test err (l271)] 19527 <-- duplicate
[test err (l271)] 19527 <-- duplicate
[test err (l271)] 19527 <-- duplicate
[test err (l272)] 19513
[test err (l272)] 19513 <-- duplicate
[test err (l272)] 19513 <-- duplicate
[test err (l272)] 19513 <-- duplicate