Nginx using as load balancer

Basic HTTP server features

Serving static and index files, autoindexing; open file descriptor cache;
Accelerated reverse proxying with caching; simple load balancing and fault tolerance;
Accelerated support with caching of FastCGI, uwsgi, SCGI, and memcached servers; simple load balancing and fault tolerance;
Modular architecture. Filters include gzipping, byte ranges, chunked responses, XSLT, SSI, and image transformation filter. Multiple SSI inclusions within a single page can be processed in parallel if they are handled by proxied or FastCGI/uwsgi/SCGI servers;
SSL and TLS SNI support.
Other HTTP server features

Name-based and IP-based virtual servers;
Keep-alive and pipelined connections support;
Flexible configuration;
Reconfiguration and upgrade of an executable without interruption of the client servicing;
Access log formats, buffered log writing, fast log rotation, and syslog logging;
3xx-5xx error codes redirection;
The rewrite module: URI changing using regular expressions;
Executing different functions depending on the client address;
Access control based on client IP address, by password (HTTP Basic authentication) and by the result of subrequest;
Validation of HTTP referer;
The PUT, DELETE, MKCOL, COPY, and MOVE methods;
FLV and MP4 streaming;
Response rate limiting;
Limiting the number of simultaneous connections or requests coming from one address;
Embedded Perl.

Load balancing methods

The following load balancing mechanisms (or methods) are supported in nginx:

round-robin — requests to the application servers are distributed in a round-robin fashion,
least-connected — next request is assigned to the server with the least number of active connections,
ip-hash — a hash-function is used to determine what server should be selected for the next request (based on the client’s IP address).
Default load balancing configuration

The simplest configuration for load balancing with nginx may look like the following:

http {
upstream myapp1 {

server {
listen 80;

location / {
proxy_pass http://myapp1;
In the example above, there are 3 instances of the same application running on srv1-srv3. When the load balancing method is not specifically configured, it defaults to round-robin. All requests are proxied to the server group myapp1, and nginx applies HTTP load balancing to distribute the requests.

Reverse proxy implementation in nginx includes load balancing for HTTP, HTTPS, FastCGI, uwsgi, SCGI, and memcached.

To configure load balancing for HTTPS instead of HTTP, just use “https” as the protocol.

When setting up load balancing for FastCGI, uwsgi, SCGI, or memcached, use fastcgi_pass, uwsgi_pass, scgi_pass, and memcached_pass directives respectively.

Least connected load balancing

Another load balancing discipline is least-connected. Least-connected allows controlling the load on application instances more fairly in a situation when some of the requests take longer to complete.

With the least-connected load balancing, nginx will try not to overload a busy application server with excessive requests, distributing the new requests to a less busy server instead.

Least-connected load balancing in nginx is activated when the least_conn directive is used as part of the server group configuration:

upstream myapp1 {
Session persistence

Please note that with round-robin or least-connected load balancing, each subsequent client’s request can be potentially distributed to a different server. There is no guarantee that the same client will be always directed to the same server.

If there is the need to tie a client to a particular application server — in other words, make the client’s session “sticky” or “persistent” in terms of always trying to select a particular server — the ip-hash load balancing mechanism can be used.

With ip-hash, the client’s IP address is used as a hashing key to determine what server in a server group should be selected for the client’s requests. This method ensures that the requests from the same client will always be directed to the same server except when this server is unavailable.

To configure ip-hash load balancing, just add the ip_hash directive to the server (upstream) group configuration:

upstream myapp1 {

Weighted load balancing

It is also possible to influence nginx load balancing algorithms even further by using server weights.

In the examples above, the server weights are not configured which means that all specified servers are treated as equally qualified for a particular load balancing method.

With the round-robin in particular it also means a more or less equal distribution of requests across the servers — provided there are enough requests, and when the requests are processed in a uniform manner and completed fast enough.

When the weight parameter is specified for a server, the weight is accounted as part of the load balancing decision.

upstream myapp1 {
server weight=3;

With this configuration, every 5 new requests will be distributed across the application instances as the following: 3 requests will be directed to srv1, one request will go to srv2, and another one — to srv3.

It is similarly possible to use weights with the least-connected and ip-hash load balancing in the recent versions of nginx.

Health checks

Reverse proxy implementation in nginx includes in-band (or passive) server health checks. If the response from a particular server fails with an error, nginx will mark this server as failed, and will try to avoid selecting this server for subsequent inbound requests for a while.

The max_fails directive sets the number of consecutive unsuccessful attempts to communicate with the server that should happen during fail_timeout. By default, max_fails is set to 1. When it is set to 0, health checks are disabled for this server. The fail_timeout parameter also defines how long the server will be marked as failed. After fail_timeout interval following the server failure, nginx will start to gracefully probe the server with the live client’s requests. If the probes have been successful, the server is marked as a live one.

Other posts


Posted on March 14, 2015, in LInux Based, Web. Bookmark the permalink. Leave a comment.

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