Why am I getting a 502 Bad Gateway using Dokku after a few hours of uptime

Question

Deployment is smooth, everything is working then I check back on the site after a day or so and its come down with a 502 bad gateway. I have more than one (now three) small nodejs express and mongoose apps running inside dokku, when I mean small I’m talking a single page app and a sign up form. Database is hosted elsewhere.

I have tried increasing server size, which seemed to delay the problem a little, but mostly it seems pretty random and if it was a ram problem my understanding is dokku should reboot the app anyway.

What else could I try?

Bobby · Accepted Answer

Hello, What I would recommend following these steps in case that you are having any problems with your nginx server and you are unsure on what the problem is: Check if nginx is running: systemctl status nginx If nginx is running you should see something like this: ● nginx.service - The nginx HTTP Server Loaded: loaded (/lib/systemd/system/nginx.service; enabled; vendor preset: enabled) Active: active (running) since Tue 2019-11-19 09:37:46 UTC; 2 days ago Docs: https://httpd.nginx.org/docs/2.4/ If nginx is not running then the output would look like this: ● nginx.service - The nginx HTTP Server Loaded: loaded (/lib/systemd/system/nginx.service; enabled; vendor preset: enabled) Active: inactive (dead) since Fri 2019-11-22 08:41:01 UTC; 39s ago Docs: https://httpd.nginx.org/docs/2.4/ If nginx is not running you could start it with: systemctl start nginx Then check the status agian and make sure that nginx remains running. If nginx did not start after a reboot, you could enable it so that it starts after the next reboot: systemctl enable nginx Check your nginx config syntax: nginx -t If you get an error, you would need to fix that problem and then you could restart nginx: systemctl restart nginx If you get Syntax OK when running nginx -t then your confiruation is correct, so I would recommend checking your error logs: tail -f /var/log/nginx/error.log Check the permissions of the files and folders in your document root: Find the user that your nginx service is running as: ps auxf | grep nginx If you are using Ubuntu, the user should be www-data, so you would need to make sure that your files and folders are owned by that user, so nginx could read and write to those files: chown -R www-data:www-data /var/www/yourdomain.com Check if nginx is binding to the default ports: netstat -plant | grep '80\|443' Check if ufw allows TCP connections on port 80 and 443: ufw status If this is the case, you can follow the steps from this article here on how to configure your ufw: https://www.digitalocean.com/community/tutorials/how-to-set-up-a-firewall-with-ufw-on-ubuntu-18-04 That is pretty much it, with all of the above information you should be able to narrow down the problem. For more information I would suggest checking out this article here: https://www.digitalocean.com/community/tutorials/how-to-troubleshoot-common-site-issues-on-a-linux-server And here is also a quick video demo on how to do that as well: Hope that this helps!Regards,BobbySource: How to Troubleshoot Common Nginx Issues on Linux Server?

horriblefactory · Answer

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Why am I getting a 502 Bad Gateway using Dokku after a few hours of uptime

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