# Load Balancer
Simple guide to setup a load balancer based on nginx.
## Backend Server
First we need to create two backend-server:
```bash
cd /etc/nginx/sites-available
sudo vi backend_server
```
```nginx
server {
listen 127.0.0.1:8080;
server_name _;
root /var/www/backend/srv1;
index index.html;
location / {
try_files $uri $uri/ =404;
}
}
server {
listen 127.0.0.1:8081;
server_name _;
root /var/www/backend/srv2;
index index.html;
location / {
try_files $uri $uri/ =404;
}
}
```
enable the new servers and validate configuration:
```bash
sudo ln -s /etc/nginx/sites-available/backend_server backend_server
sudo nginx -t
```
restart nginx
```bash
sudo systemctl reload nginx
```
to verify the two servers are running:
```bash
sudo netstat -anp | grep -E "8080|8081"
```
## simple html
the new webserver need an `index.html`
```bash
cd /var/www/
sudo mkdir -p backend/srv1
sudo mkdir -p backend/srv2
```
### srv1
`index.html` of server one:
```bash
sudo vi backend/srv1/index.html
```
```html
Welcome!
Hello World! I am backend-server 1!
```
### srv2
`index.html` of server two:
```bash
sudo vi backend/srv2/index.html
```
```html
Welcome!
Hello World! I am backend-server 2!
```
## Load Balancer
lets create a new server as load balancer.
```bash
cd /etc/nginx/sites-available
sudo vi loadbalancer
```
```nginx
upstream my_backend_server {
# default round-robin; other options: least_conn; ip_hash;
# or using custom hash based on e.g. cookies: hash $cookie_ consistent;
server 127.0.0.1:8080;
server 127.0.0.1:8081;
}
server {
listen 80;
server_name *mydomain*;
location / {
proxy_pass http://my_backend_server;
}
}
```
enable the new configuration & verify:
```bash
sudo ln -f -s /etc/nginx/sites-available/loadbalancer *mydomain*
sudo nginx -t
```
restart nginx:
```bash
sudo systemctl reload nginx
```
## Test
load the website and refresh it serveral times...
### simulate server crash
simply change the listen port of one the backend-server (e.g. srv2 listen on 8082). Restart nginx. Retry the test.
### simulate server failure
before `location` add directive: `return 500;`. Restart nginx. Retry the test.
## Handle server failure
edit load balancer configuration:
```nginx
[...]
location / {
proxy_pass http://my_backend_server;
proxy_next_upstream timeout http_500;
}
[...]
```
validate configuration, restart nginx and repeat the server failure test.