nginx_install.md

1. Add nginx repository:

$ sudo yum install epel-release

2. Install nginx (on Centos 7)

$ sudo yum install nginx

3. We need say to SElinux that he need to allow HTTP trafic:

$ setsebool -P httpd_can_network_connect 1

4. Start nginx and add him to autorun:

$ sudo systemctl start nginx
$ sudo systemctl enable nginx

5. If you want to allow HTTP and HTTPS trafic do next commands in terminal:

$ sudo firewall-cmd --permanent --zone=public --add-service=http 
$ sudo firewall-cmd --permanent --zone=public --add-service=https
$ sudo firewall-cmd --reload

6. Open main config file of nginx : $ sudo vim etc/nginx/nginx.config

make sure it have this fields:

user nginx;
worker_processes 1;   #put here the number of your CPU cores on your machine

...

events {
    worker_connections 1024;   #depends on your system, here you write number of maximum simultaneously connections
}

http {
    
    ...
    
    include /etc/nginx/conf.d/*.conf;
    include /etc/nginx/sites-enabled/*;  #make sure this path is here, because it is the main path to our next configuration file, in which we will write adresses of our actually servers
    }
}

7. create new folder in nginx( if it does not exist yet), in which will be our default config file (it can be there already):

$ mkdir /etc/nginx/sites-enable
$ vi /etc/nginx/sites-enable/default

This default config file should be configured like this:

upstream project {       # project - is name of group of servers that need to manage 
    hash $remote_addr;   # method of balancing using IP address as a key to balance users
    server 192.168.103.166:8080;    #next 3 fields describes to which servers will our nginx serve as proxy
    server 192.168.103.247:8080;
    server 192.168.103.221:8080;
}

server {
    listen 80;         # listening to this port, if something come it will redirect to "location" field
        location / {
        proxy_pass http://project;   #this line tells us, that every request that come on our address on 80 port will redirect to group of my servers
    }                                #make sure that proxy_pass field have exactly same name as the name of upstream
}

8. Reload and restart nginx

$ systemctl reload nginx
$ systemctl restart nginx

9. Your nginx load ballancer is ready to use! To access OMS file just call your local IP address + /OMS

example:
192.168.103.172/OMS

10. But if you dont want to write "/OMS" after IP addres just do next steps on your server (where tomcat is):

a) open this file : $ vi /var/lib/tomcat/webapps/ROOT/index.jsp
b) in oppened file on the top write next line:
   <% response.sendRedirect("http://IPaddressOfYourBallancer/OMS"); %>

example <% response.sendRedirect("http://192.168.103.172/OMS"); %>

c)$ systemctl restart tomcat

11. Also if you want that your app servers be only reachable from ballancer, and someone can`t use their IP addresses instead of IP address of balancer:

# [port] and [ip] need to write without "[" and "]"
$ iptables -A INPUT -p tcp -s [ip] --dport [port] -j ACCEPT
$ iptables -A INPUT -p tcp -s 0.0.0.0/0 --dport [port] -j DROP
$ iptables-save
# here [ip] - is IP address of your balancer, throw it will be all trafic passed
# [port] - port that you will open for one [ip] and close to all other internet IP addresses

12. DONE! Enjoy your work, drink some coffe and be cool! =)