nginx - port forwarding to another container - docker

Question

I'm trying to use nginx container which will be used to port forwarding communication to other containers such as Ansible/GIT/Jenkins etc ....
When using nci-ansible-ui as Ansible, I can reach the Ansible UI using the external host server IP http://10.97.98.6:3000 (which is according the instructions). Yet, when trying to use the nginx to port forward to this container - the 404 and 502 errors appear in the log while the web page is not properly loaded... note that in such case, I would like to use http://10.97.98.6/Master_Ansible as the URL. Note that http://172.18.0.5 is the docker network IP given to the container...
server {
listen 80;
listen 3000;
server_name localhost;
#charset koi8-r;
access_log /var/log/nginx/access.log main;
error_log /var/log/nginx/error.log warn;
root /etc/nginx/html;
index index.html index.php;
#charset koi8-r;
location / {
root /etc/nginx/html;
try_files $uri /$uri $uri/ =404;
}
location /Master_Ansible {
proxy_pass http://172.18.0.5:3000;
proxy_set_header Host $host;
proxy_set_header X-Real-IP $remote_addr;
proxy_set_header X-Forwarded-For $proxy_add_x_forwarded_for;
proxy_set_header X-Forwarded-Proto http;
proxy_max_temp_file_size 0;
proxy_connect_timeout 150;
proxy_send_timeout 100;
proxy_read_timeout 100;
proxy_buffer_size 8k;
proxy_buffers 4 32k;
proxy_busy_buffers_size 64k;
proxy_temp_file_write_size 64k;
}
}
Any idea about this?