In this article, we will show you how to setup basic load balancing in NGINX. This will help you to balance the requests across your web server instances so that they are delivered as evenly as possible. First, let’s take a look at what a typical web server configuration looks like: 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 61 62 63 64 65 66 67 68 69 70 71 72 73 74 75 76 77 78 79 80 81 82 83 84 85 86 87 88 89 90 91 92 93 94 95 96 97 98 99 100 101 102 103 104 105 106 107 108 109 110 111 112 113 114 115 116 117 118 119 120 121 122 123 124 125 126 127 128 129 130 131 132 133 134 135 136 137 138 139 140 141 142 143 144 145 146 147 148 149 150 151 152 153 154 155 156 157 158 159 160 161 162 163 164 165 166 167 168 169 170 171 172 173 174 175 176 177 178 179 180 181 182 183 184 185 186 187 188 189 190 191 192 193 194 195 196 197 198 199 200 201 202 203 204 205 206 207 208 209 210 211 212 213 214 215 216 217 218 219 220 221 222 223 224 225 226 227 228 229 230 231 232 233 234 235 236 237 238 239 240 241 242 243 244 245 246 247 248 249 250 251 252 253 254 255 256 257 258 259 260 261 262 263 264 265 266 267 268 269 270 271 272 273 274 275 276 277 278 279 280 281 282 283 284 285 286 287 288 289 290 291 292 293 294 295 296 297 298 299 300 301 302 303 304 305 306 307 308 309 310 311 312 313 314 315 316 317 318 319 320 321 322 323 324 325 326 327 328 329 330 331 332 333 334 335

How NGINX Load Balancing Works

The basic principle of a Load Balancer is that it sits between the user and a set of servers, and proxies requests for them. Usually this is done with two or more servers, so that traffic can be distributed more easily between them.

Most of the configuration happens in how NGINX selects which server to route to. The default is round-robin, which will send requests to each server in order, ensuring an equal load distribution.

However, it’s not always that simple. Many web applications require some form of session persistence, which means that the user must be accessing the same server for their whole session. For example, a shopping cart might be stored locally on one application server, and if the user switches servers mid-session, the application could glitch out. Of course, many of these scenarios can be fixed with better application infrastructure and centralized datastores, but session persistence is required by many people.

In NGINX, the set of servers that you route to is known as an upstream, and is configured like an enumerated list of addresses:

These upstreams have a lot of options; here, we’ve set a weight, which will prioritize this server more often (particularly useful if you have different sizes). You can also set the max connnections and various timeouts. If you’re using NGINX Plus, you can also set up health checks so that connections don’t get routed to unhealthy servers.

The most basic form of session persistence is using an IP hash. NGINX will use the IP to identify users and then make sure that these users don’t switch servers mid-session:

The IP hash is required for socket-based applications and anything requiring persistence. If you don’t want to use the IP address, you can customize this hash:

If you don’t need any kind of session persistence, you can make the round-robin selection a little smarter by selecting which server has the least connections:

Or, based on which one is currently responding fastest:

NGINX Plus has a few other forms of session persistence, but IP hashing will work for most applications.

Proxying to the Backend

Once you’ve got your backend configured, you can send requests to it from within your location blocks, using proxy_pass with a URI to the backend.

Of course, if you’re using HTTPS, you’ll need to send the request with HTTPS: