Varnish cache responese with “Set-Cookie” header

cookieshttpvarnish

I have a page which sends a "Set-Cookie" header for something like the language depending on the URL. The thing is this page will get a fairly high hit rate but it's not an option right now to strip the "Set-Cookie" header so that Varnish 4 will cache it.

The documentation only shows how to unset beresp.http.set-cookie or that I can add the cookie to the hash with hash_data(req.http.cookie). As far as I see, adding the cookie to the hash only apply to request Cookies not to the cookies set by the backend.

I am pretty sure vmod_header could be part of the solution but how would I use it to cache a cookie that I match with beresp.http.Set-Cookie == "language=en_us; path=/; domain=mydomain.tld" and cache this response?

Best Answer

The cache key (aka the hash computed in hash_data) is created when receiving the request. The response from the server is not yet received. You cannot change it afterwards.

The two options I can see is :

either disabling the cache of response coming with Set-Cookie header (what I think is maybe done by defautl by varnish)
or list the parameters in the incoming request you use in your Cookie computation (url, host, accept-language...) and add them to the request hash using hash_data

Related Solutions

Nginx – Ignoring GET parameters in Varnish VCL

If you need to leave the key=SOMEALPHANUM intact to the backend in case not delivered from cache, then it might be better to regsub within the vcl_hash function instead, as this won't really alter the url but instead it just alters the hash of the key.

sub vcl_hash {
  if(req.http.host ~ "the-site-in-question.com" & req.url ~ "^/api/") {
    set req.http.X-Sanitized-URL = req.url;
    set req.http.X-Sanitized-URL = regsub(req.http.X-Sanitized-URL, "&key=[A-Za-z0-9]+", "");
    set req.hash += req.http.X-Sanitized-URL;
  } else {
    set req.hash += req.url;
  }
  set req.hash += req.http.host;
  hash;
}

How to make Varnish ignore, not delete cookies

By default Varnish doesn't cache requests with a Cookie header:

http://varnish-cache.org/svn/trunk/varnish-cache/bin/varnishd/default.vcl

  sub vcl_recv {
(...)
  if (req.http.Authorization || req.http.Cookie) {
        /* Not cacheable by default */
        return (pass);
    }
    return (lookup);

You need to code the behaviour you want into the configuration. Be aware that the Cookie is part of the client request, not the "page" (object, really). The "page" (object) comes with a "Set-Cookie" header - that's the one that will be cached.

Also, "Vary: Cookie" doesn't mean "do not cache". It means cache one object for every value of Cookie received.

If your application doesn't generate any content based on Cookie, it's probably safe to ignore it:

-      if (req.http.Authorization || req.http.Cookie) {
+      if (req.http.Authorization) {

Do some tests and you will get the hang of it. Hope this helps.

Best Answer

Related Solutions

Nginx – Ignoring GET parameters in Varnish VCL

How to make Varnish ignore, not delete cookies

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