Nginx, load-balancing using sticky and least connections algorithms simulteniously

We use Nginx as load-balancer for our websocket application. Every backend server keeps session information so every request from client must be forwarded on the same server. So we use ip_hash directive to achieve this:

upstream app {     ip_hash;     server 1; } 

The problem appears when we want to add another backend server:

upstream app {     ip_hash;     server 1;     server 2; } 

New connections go to server 1 and server 2 - but this is not what we need in this situation as load on server 1 continues to increase - we still need sticky sessions but least_conn algorithm enabled too - so our two servers receive approximately equal load.

We also considered using Nginx-sticky-module but the documentaton says that if no sticky cookie available it will fall back to round-robin default Nginx algorithm - so it also does not solve a problem.

So the question is can we combine sticky and least connections logic using Nginx? Do you know which other load balancers solve this problem?

2 Answers

Answers 1

Probably using the split_clients module could help

upstream app {     ip_hash;     server 127.0.0.1:8001; }  upstream app_new {     ip_hash;     server 127.0.0.1:8002; }  split_clients "${remote_addr}AAA" $upstream_app {     50% app_new;     *   app; } 

This will split your traffic and create the variable $upstreap_app the one you could use like:

server {    location /some/path/ {    proxy_pass http://$upstream_app; } 

This is a workaround to the least_conn and the load balancer that work with sticky sessions, the "downside" is that if more servers need to be added, a new stream needs to be created, for example:

split_clients "${remote_addr}AAA" $upstream_app {     30% app_another_server;     30% app_new;     *   app; } 

For testing:

for x in {1..10}; do \   curl "0:8080?token=$(LC_ALL=C; cat /dev/urandom | tr -dc 'a-zA-Z0-9' | fold -w 32 | head -n 1)"; done 

More info about this module could be found in this article (Performing A/B testing)

Answers 2

You can easily achieve this using HAProxy and I indeed suggest going through it thoroughly to see how your current setup can benefit.

With HA Proxy, you'd have something like:

backend nodes     # Other options above omitted for brevity     cookie SRV_ID prefix     server web01 127.0.0.1:9000 cookie check     server web02 127.0.0.1:9001 cookie check     server web03 127.0.0.1:9002 cookie check 

Which simply means that the proxy is tracking requests to-and-fro the servers by using a cookie.

However, if you don't want to use HAProxy, I'd suggest you setup you change your session implementation to use an in-memory DB such as redis/memcached. This way, you can use leastconn or any other algorithm without worrying about sessions.

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