Day: January 7, 2019

Starting Express.js applications with PM2

I recently ran into an issue with PM2. I have created a “helloworld” applications using Express.js.

[root@nodejs projects]# express helloworld
 warning: the default view engine will not be jade in future releases
   warning: use --view=jade' or--help' for additional options
 create : helloworld/
    create : helloworld/public/
    create : helloworld/public/javascripts/
    create : helloworld/public/images/
    create : helloworld/public/stylesheets/
    create : helloworld/public/stylesheets/style.css
    create : helloworld/routes/
    create : helloworld/routes/index.js
    create : helloworld/routes/users.js
    create : helloworld/views/
    create : helloworld/views/error.jade
    create : helloworld/views/index.jade
    create : helloworld/views/layout.jade
    create : helloworld/app.js
    create : helloworld/package.json
    create : helloworld/bin/
    create : helloworld/bin/www
 change directory:
      $ cd helloworld
 install dependencies:
      $ npm install
 run the app:
      $ DEBUG=helloworld:* npm start

The application started without issues with npm start.

Next I started the application with PM2

[root@nodejs helloworld]# pm2 start app.js

PM2 displayed the application as “online”, but it constantly restarted and was not accessible.

I found the solution here

[root@nodejs helloworld]# pm2 start bin/www

did the trick for me.


nginx + node.js + CentOS 7 = 502 Bad Gateway

I have setup a new Node.js / Express development environment on a CentOS 7 VM. I ‘ll describe the details in another post later.

To test my setp, I created a new Express application “helloworld”. The application listens on port 3000 and I was able to connect to the application using a browser.

Next, I configured NGINX as reverse proxy to use port 80 to access the helloworld application.

But I got an error

I checked the logs 

[root@nodejs ~]# cat /var/log/audit/audit.log | grep nginx | grep denied

and got

type=AVC msg=audit(1546783734.750:239): avc:  denied  { name_connect } for  pid=11084 comm="nginx" dest=3000 scontext=system_u:system_r:httpd_t:s0 tcontext=system_u:object_r:ntop_port_t:s0 tclass=tcp_socket permissive=0

My best guess was SELinux.I checked, if SELinux was enabled.

[root@nodejs ~]# sestatus

 SELinux status:                 enabled
 SELinuxfs mount:                /sys/fs/selinux
 SELinux root directory:         /etc/selinux
 Loaded policy name:             targeted
 Current mode:                   enforcing
 Mode from config file:          enforcing
 Policy MLS status:              enabled
 Policy deny_unknown status:     allowed
 Max kernel policy version:      31

Next I checked the settings for httpd.

[root@nodejs ~]# getsebool -a | grep httpd
 httpd_anon_write --> off
 httpd_builtin_scripting --> on
 httpd_can_check_spam --> off
 httpd_can_connect_ftp --> off
 httpd_can_connect_ldap --> off
 httpd_can_connect_mythtv --> off
 httpd_can_connect_zabbix --> off
 httpd_can_network_connect --> off 
 httpd_can_network_connect_cobbler --> off
 httpd_can_network_connect_db --> off
 httpd_can_network_memcache --> off
 httpd_can_network_relay --> off
 httpd_can_sendmail --> off

So, httpd_can_network_connect was set to “Off”. This blocks the connection from the reverse proxy to the node.js application. As a result, you get the 502 Bad gateway error.

To enable the setting, execute the following command from the shell.

[root@nodejs ~]# setsebool -P httpd_can_network_connect on

You do not need to reboot the machine or SELinux.