Nginx set session-cookie before upstreams are hit

nginxsession

We have a nginx-reverse-proxy/cache and multiple backend-servers.

My current problem with our setup is that if a user hits a cached site he / she does not get a session-cookie set, as the backend is not hit.
This is clearly the expected behavior.

In our case, however, I want the reverse-proxy to send a session-cookie with the cached response even before any of the backend-servers are hit.

I know I can use

 add_header Set-Cookie

for this but how can I

make sure the cookie is only set once?
generate a cookie in the form of a uuid which is not hardcoded?

Best Answer

You could try to replicate the session cookie generating logic of your application software with nginx lua language.

However, a better way to implement this would be to use a JavaScript on your page that calls an URL in your page where it gets a session cookie.

Related Solutions

Nginx – How to Set Up as a Caching Reverse Proxy

I don't think that there is a way to explicitly invalidate cached items, but here is an example of how to do the rest. Update: As mentioned by Piotr in another answer, there is a cache purge module that you can use. You can also force a refresh of a cached item using nginx's proxy_cache_bypass - see Cherian's answer for more information.

In this configuration, items that aren't cached will be retrieved from example.net and stored. The cached versions will be served up to future clients until they are no longer valid (60 minutes).

Your Cache-Control and Expires HTTP headers will be honored, so if you want to explicitly set an expiration date, you can do that by setting the correct headers in whatever you are proxying to.

There are lots of parameters that you can tune - see the nginx Proxy module documentation for more information about all of this including details on the meaning of the different settings/parameters: http://nginx.org/r/proxy_cache_path

http {
  proxy_cache_path  /var/www/cache levels=1:2 keys_zone=my-cache:8m max_size=1000m inactive=600m;
  proxy_temp_path /var/www/cache/tmp; 


  server {
    location / {
      proxy_pass http://example.net;
      proxy_cache my-cache;
      proxy_cache_valid  200 302  60m;
      proxy_cache_valid  404      1m;
    }
  }
}

Nginx – Controlling Nginx proxy target using a cookie

Similar to this answer. Nginx's idiomatic approach to this kind of problems is via map.

Basically, you define a map in http section

map $cookie_proxy_override $my_upstream {
  default default-server-or-upstream;
  ~^(?P<name>[\w-]+) $name;
}

Then you simply use $my_upstream in location section(s):

location /original-request {
  proxy_pass http://$my_upstream$uri;
}

Nginx evaluates map variables lazily, only once (per request) and when you are using them.

Best Answer

Related Solutions

Nginx – How to Set Up as a Caching Reverse Proxy

Nginx – Controlling Nginx proxy target using a cookie

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