Nginx proxy_pass to docker container doesn't work - python-3.x

Question

I have two identiacal docker containers running on different ports on CentOS7 server. Older version runs on port 81, newer one on port 8080 (82,83 were checked as well).
When I'm trying to proxy second container and change port from 81 to 8080 I receive nginx error message (HTTP/1.1 502 Bad Gateway).
Nginx is not in a container. I just have it installed on the server.
Here is my proxy_pass setting:
location / {
proxy_pass http://0.0.0.0:8080/;
}
And some additional information:
nginx -t
nginx: the configuration file /etc/nginx/nginx.conf syntax is ok
nginx: configuration file /etc/nginx/nginx.conf test is successful
If I try to access containers directly via their ports everything works fine.
curl 0.0.0.0:81
{"msg":"Phone Masks service"}
curl 0.0.0.0:8080
{"msg":"Phone Masks service"}
nginx version: nginx/1.16.1
Docker version 19.03.4, build 9013bf583a
Full server config is pretty standard, I didn't change anything except proxy_pass setting
server {
listen 80 default_server;
listen [::]:80 default_server;
server_name _;
root /usr/share/nginx/html;
# Load configuration files for the default server block.
include /etc/nginx/default.d/*.conf;
location / {
proxy_pass http://0.0.0.0:8080/;
}
error_page 404 /404.html;
location = /40x.html {
}
error_page 500 502 503 504 /50x.html;
location = /50x.html {
}
}
The command I use to start the container:
sudo docker run --rm -it -p 8080:8080 -e PORT="8080" api
sudo docker ps
CONTAINER ID IMAGE COMMAND CREATED STATUS PORTS NAMES
47ef127e3e49 api "/start.sh" 26 minutes ago Up 26 minutes 80/tcp, 0.0.0.0:8080->8080/tcp infallible_borg
5d5fe891ba30 api "/start.sh" 7 hours ago Up 7 hours 80/tcp, 0.0.0.0:81->81/tcp hopeful_cerf

Answer 1

This is SElinux related:
setsebool -P httpd_can_network_connect true
According to this thread:
The second one [httpd_can_network_connect] allows httpd modules and scripts to make outgoing connections to ports which are associated with the httpd service. To see a list of those ports run semanage port -l | grep -w http_port_t