Nginx serves node app then randomly throws 502 errors - node.js

Question

I am trying to run a node app (using express) on port 3000 with nginx.
This is my nginx.conf for the site:
server {
listen [::]:80 ipv6only=off;
server_name website.dev;
location / {
proxy_pass http://127.0.0.1:3000;
proxy_set_header Host $http_host;
}
}
I'm running the node app through a nodemon task. I'm also running a gulp watch task that compiles less to css, browserify, babelify, etc.
The problem I'm having is that nginx will serve the node app fine for about 30 seconds, then (apparently randomly) start serving 502 errors. The nodemon task doesn't stop during these times, and the gulp task doesn't run either.
I can't find any errors happening in the node application itself, and nothing shows up in error.log or access.log for nginx.
I've verified that the node app is actually running on port 3000 and that nginx is listening on port 80.
Here is the output of netstat -nlt:
Proto Recv-Q Send-Q Local Address Foreign Address State
tcp 0 0 0.0.0.0:22 0.0.0.0:* LISTEN
tcp 0 0 0.0.0.0:34490 0.0.0.0:* LISTEN
tcp 0 0 0.0.0.0:111 0.0.0.0:* LISTEN
tcp6 0 0 :::22 :::* LISTEN
tcp6 0 0 :::3000 :::* LISTEN
tcp6 0 0 :::111 :::* LISTEN
tcp6 0 0 :::80 :::* LISTEN
tcp6 0 0 :::42481 :::* LISTEN
Finally, after a couple of minutes, nginx goes back to serving the app again for about 30 seconds, and repeat.
If I run curl localhost:3000 I get my node app. Even though nginx will still be throwing 502 errors.

Answer 1

Working nginx conf file looks like below,
upstream project{
server 127.0.0.1:3000;
#you can add multiple nodes here for load balancing
}
server{
listen 80;
server_name website.dev;
location / {
proxy_pass http://project;
}
}

Answer 2

It turned out to be a zombie vagrant box.
I noticed that after running vagrant halt I still got the nginx 502 page. So I went looking for another vagrant install.
There turned out to be a vagrant box still running that was not showing up on vagrant global-status and was not found by Vagrant Manager.
The host machine, for whatever reason, was switching between the boxes it was referring to randomly, which is why I was randomly getting 502 errors (from the zombie box).
Deleting the box from .vagrant/machines/ solved the issue.