I have Nginx set up as a load balancer with cookie-based stickiness. The logic is:
If the cookie is NOT there, use round-robbing to choose a server from cluster.
If the cookie is there, go to the server that is associated with the cookie value. Server is then responsible for setting the cookie.
What I want to add is this:
If the cookie is there, but server is down, fallback to round-robbing step to choose next available server.
So actually I have load balancing and want to add failover support on top of it.
I have managed to do that with the help of error_page directive, but it doesn't work as I expected it to.
The problem: 504 (and the fallback associated with it) fires only after 30s timeout even if the server is not physically available.
So what I want Nginx to do is fire a 504 (or any other error, doesn't matter) immediately (I suppose this means: when TCP connection fails). This is the behavior we can see in browsers: if we go directly to server when it is down, browser immediately tells us that it can't connect. Moreover, Nginx seems to be doing this for 502 error: if I intentionally misconfigure my servers, Nginx fires 502 immediately.
Configuration (stripped down to basics):
http {
upstream my_cluster {
server 192.168.73.210:1337;
server 192.168.73.210:1338;
}
map $cookie_myCookie $http_sticky_backend {
default 0;
value1 192.168.73.210:1337;
value2 192.168.73.210:1338;
}
server {
listen 8080;
location @fallback {
proxy_pass http://my_cluster;
}
location / {
error_page 504 = @fallback;
# Create a map of choices
# see https://gist.github.com/jrom/1760790
set $test HTTP;
if ($http_sticky_backend) {
set $test "${test}-STICKY";
}
if ($test = HTTP-STICKY) {
proxy_pass http://$http_sticky_backend$uri?$args;
break;
}
if ($test = HTTP) {
proxy_pass http://my_cluster;
break;
}
return 500 "Misconfiguration";
}
}
}
Disclaimer: I am pretty far from systems administration of any kind, so there may be some basics that I miss here.
EDIT: I'm interested in solution with standard free version of Nginx, not Nginx Plus. Thanks.
