Create 15_load_balancer.md

2026-07-23 09:52:14 +00:00 · 2026-06-09 10:57:50 +02:00
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+# 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
+<html>
+    <head>
+        <title>Welcome!</title>
+    </head>
+    <body>
+        <h1>Hello World! I am backend-server 1!</h1>
+    </body>
+</html>
+```
+
+### srv2
+
+`index.html` of server two:
+
+```bash
+sudo vi backend/srv2/index.html
+```
+
+```html
+<html>
+    <head>
+        <title>Welcome!</title>
+    </head>
+    <body>
+        <h1>Hello World! I am backend-server 2!</h1>
+    </body>
+</html>
+```
+
+## 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_<cookie-name> 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.