Varnish Cache Expiring Objects Too Quickly

Question

I've been having a problem with my varnish (v3.0.2) cache where it keeps resetting the cache of an object after less than 60 seconds despite having a TTL of 24h, cookies stripped, content encoding normalized, non-critical headers unset, Cache-Control set to public, s-maxage=86400 etc.

For some reason, if you access the following URL repeatedly over a minute, you can see that the Age creeps up and then hits zero (with X-Cache returning MISS):

http://data.eyewire.org/volume/83329/chunk/0/1/0/1/tile/xz/32:64

There are no n_lru_nuked objects and the cache is over 60GB. I watched the varnishlog and may have seen something with ExpBan going on, but I can't for the life of me figure out why.

Here are some key parts to my vcl file:

sub vcl_recv {
  set req.grace = 120s;

   # normalize Accept-Encoding to reduce vary
  if (req.http.Accept-Encoding) {
    if (req.http.User-Agent ~ "MSIE 6") {
      unset req.http.Accept-Encoding;
    } 
    elsif (req.http.Accept-Encoding ~ "gzip") {
      set req.http.Accept-Encoding = "gzip";
    } 
    elsif (req.http.Accept-Encoding ~ "deflate") {
      set req.http.Accept-Encoding = "deflate";
    } 
    else {
      unset req.http.Accept-Encoding;
    }
  }

  # This uses the ACL action called "purge". Basically if a request to
  # PURGE the cache comes from anywhere other than localhost, ignore it.
  if (req.request == "PURGE") 
    {if (!client.ip ~ purge)
      {error 405 "Not allowed.";}
    return(lookup);}

  if (req.http.Upgrade ~ "(?i)websocket") {
    return (pipe);
  }

  # ....

  if ( req.http.host ~ "data\.eyewire\.org" ) {
    unset req.http.Cookie;
    unset req.http.Accept-Language;
    unset req.http.Expires;
    unset req.http.Cache-Control;
    unset req.http.User-Agent;
    return(lookup);
  }

  # ....
}


sub vcl_fetch {
  # ....

  if ( req.http.host ~ "data.eyewire.org" ) {
    if ( req.url ~ "^/volume" ) {
      unset beresp.http.Set-Cookie;
      set beresp.ttl = 24h;
      set beresp.http.Cache-Control = "public, s-maxage=86400";
      set beresp.http.X-TTL = beresp.ttl;
      return(deliver);
    }
    elsif (req.url ~ "^/cell") {
      set beresp.ttl = 1h;
      return(hit_for_pass);
    }
  }
}

# from http://blog.bigdinosaur.org/adventures-in-varnish/
sub vcl_pass {
  set bereq.http.connection = "close";
  if (req.http.X-Forwarded-For) {
      set bereq.http.X-Forwarded-For = req.http.X-Forwarded-For;
  }
  else {
      set bereq.http.X-Forwarded-For = regsub(client.ip, ":.*", "");
  }
}

# from http://blog.bigdinosaur.org/adventures-in-varnish/
sub vcl_pipe {
  #we need to copy the upgrade header
  if (req.http.upgrade) {
      set bereq.http.upgrade = req.http.upgrade;
      set bereq.http.connection = req.http.connection;
  }

  set bereq.http.connection = "close";
  if (req.http.X-Forwarded-For) {
      set bereq.http.X-Forwarded-For = req.http.X-Forwarded-For;
  }
  else {
      set bereq.http.X-Forwarded-For = regsub(client.ip, ":.*", "");
  }
}

# from http://blog.bigdinosaur.org/adventures-in-varnish/
sub vcl_hit {
  if (req.request == "PURGE") {
      purge;
      error 200 "Purged.";
  }
}

# from http://blog.bigdinosaur.org/adventures-in-varnish/
sub vcl_miss {
  if (req.request == "PURGE") {
      purge;
      error 200 "Purged.";
  }
}

sub vcl_deliver {  
    # Display hit/miss info
    if (obj.hits > 0) {
      set resp.http.X-Cache = "HIT";
      set resp.http.X-Cache-Hits = obj.hits;
    }
    else {
        set resp.http.X-Cache = "MISS";
    }

    # Security Non-Disclosure
    remove resp.http.X-Varnish;
    remove resp.http.X-Powered-By;
    remove resp.http.Server;

    return(deliver);
}

Thanks!

Edit: FYI: I had to revert some changes to my VCL to solve a problem in production, but the problem is still essentially the same.

Answer 1

For what it's worth, I just upgraded to Varnish 4 and it seemed to solve the problem. During the upgrade we also removed the definition of vcl_hit and vcl_miss which included a purge directive that didn't seem like it was being hit but who knows.