the log is normal in local mode. After starting with pm2 cluster mode, the log cannot be output. The method of searching on the Internet has been tried all over, but it still doesn"t work.

version:
nodejs:9.0.0
express:4.11
log4js:2.5.3

log configuration file:

log4js.configure(
  {
    pm2: true,
    pm2InstanceVar: "INSTANCE_ID",  
    //pm2InstanceVar: 0, 
    replaceConsole: true,
    appenders: {
        stdout: {
            type: "stdout"
        },
        req: {
            type: "dateFile",
            filename: "logs/",
            pattern: "yyyy-MM-dd.log",
            alwaysIncludePattern: true
        }
    },
    categories: {
        default: { appenders: ["stdout", "req"], level: "debug" }
    }
}


);
 
var logger = log4js.getLogger("H5API");