Setting up a load balancer using nginx - nginx

Question

I am learning how to set up a load balancer, using nginx on AWS.
I set up a basic ubuntu 18.04 server on AWS, and then did the following:
sudo apt-get update
sudo apt-get upgrade -y
sudo apt-get install nginx -y
I then replaced /etc/nginx/nginx.conf with the following:
upstream backend {
server xxx.24.20.11;
server xxx.24.20.12;
}
server {
listen 80;
location / {
proxy_pass http://backend;
}
}
I then tried restarting the nginx server by doing:
sudo service nginx stop
sudo service nginx start
but I'm getting the error message:
Job for nginx.service failed because the control process exited with error code.
See "systemctl status nginx.service" and "journalctl -xe" for details.
So, I did
systemctl status nginx.service
And here's what I got:
nginx.service - A high performance web server and a reverse proxy server
Loaded: loaded (/lib/systemd/system/nginx.service; enabled; vendor preset: enabled)
Active: failed (Result: exit-code) since Wed 2019-04-03 01:13:27 UTC; 23s ago
Docs: man:nginx(8)
Process: 1822 ExecStop=/sbin/start-stop-daemon --quiet --stop --retry QUIT/5 --pidfile /run/nginx.pid (code=exited, status=0/SUCCESS)
Process: 1748 ExecStart=/usr/sbin/nginx -g daemon on; master_process on; (code=exited, status=0/SUCCESS)
Process: 1865 ExecStartPre=/usr/sbin/nginx -t -q -g daemon on; master_process on; (code=exited, status=1/FAILURE)
Main PID: 1752 (code=exited, status=0/SUCCESS)
Apr 03 01:13:27 load-balancer.xxxx.com systemd[1]: Starting A high performance web server and a reverse proxy server...
Apr 03 01:13:27 load-balancer.xxx.com nginx[1865]: nginx: [emerg] "upstream" directive is not allowed here in /etc/nginx/nginx.conf:2
Apr 03 01:13:27 load-balancer.xxx.com nginx[1865]: nginx: configuration file /etc/nginx/nginx.conf test failed
Apr 03 01:13:27 load-balancer.xxx.com systemd[1]: nginx.service: Control process exited, code=exited status=1
Apr 03 01:13:27 load-balancer.xxx.com systemd[1]: nginx.service: Failed with result 'exit-code'.
Apr 03 01:13:27 load-balancer.xxx.com systemd[1]: Failed to start A high performance web server and a reverse proxy server.
I looked at two separate tutorials, and they both use the "upstream" directive. Any ideas?
Edit:
I returned nginx.conf to its original format:
sudo cp /etc/nginx/nginx.original /etc/nginx/nginx.conf
Then, I did the following:
sudo su
echo > /etc/nginx/sites-available/load-balancer.conf
I then added the following to /etc/nginx/sites-available/load-balancer.conf
http {
upstream backend {
server docker-one.xxxxxxx.com;
server docker-two.xxxxxxx.com;
}
server {
listen 80;
server_name load-balancer.xxxxxxx.com;
location / {
proxy_pass http://backend;
}
}
}
load-balancer.xxxxxxx.com is the domain name that I am using for testing, and the docker-one and docker-two are the two domains that will be running the actual web app.
I then did a symlink:
ln -s /etc/nginx/sites-available/load-balancer.conf /etc/nginx/sites-enabled/
then I rebooted the server. When it was back up, I did the following:
sudo service nginx stop
sudo service nginx start
I got an error message telling me the nginx service failed, so I did:
systemctl status nginx.service
Which gave me the following error:
● nginx.service - A high performance web server and a reverse proxy server
Loaded: loaded (/lib/systemd/system/nginx.service; enabled; vendor preset: enabled)
Active: failed (Result: exit-code) since Wed 2019-04-03 19:42:34 UTC; 19s ago
Docs: man:nginx(8)
Process: 1549 ExecStartPre=/usr/sbin/nginx -t -q -g daemon on; master_process on; (code=exited, status=1/FAILURE)
Apr 03 19:42:34 load-balancer.xxxxxxx.com systemd[1]: Starting A high performance web server and a reverse proxy server...
Apr 03 19:42:34 load-balancer.xxxxxxx.com nginx[1549]: nginx: configuration file /etc/nginx/nginx.conf test failed
Apr 03 19:42:34 load-balancer.xxxxxxx.com systemd[1]: nginx.service: Control process exited, code=exited status=1
Apr 03 19:42:34 load-balancer.xxxxxxx.com systemd[1]: nginx.service: Failed with result 'exit-code'.
Apr 03 19:42:34 load-balancer.xxxxxxx.com systemd[1]: Failed to start A high performance web server and a reverse proxy server.

Answer 1

Overwriting whole nginx.conf you deleted http context. upstream is only allowed inside http {} block as per https://nginx.org/en/docs/http/ngx_http_upstream_module.html#upstream
Debian/ubuntu uses /etc/nginx/sites-available/* for site definitions, thats where you need to create your own config file, one per vhost if needed. And then enable it so it becomes symlinked to /etc/nginx/sites-enabled/*. Or for simplicity, use /etc/nginx/sites-available/default as existing config file, make your changes there. Save original, until you get it working. And reload nginx after said changes. Restore original /etc/nginx/nginx.conf also, ofcourse.