lacquer

Rails drop in for Varnish support. This version is adapted from Russ Smith’s gem and is in production use on posterous.com.

Install

Basic installation

sudo gem install posterous-lacquer

config/initializers/lacquer.rb

Lacquer.configure do |config|
  # Globally enable/disable cache
  config.enable_cache = true

  # Unless overridden in a controller or action, the default will be used
  config.default_ttl = 1.week

  # Can be :none, :delayed_job, :resque
  config.job_backend = :none

  # Array of Varnish servers to manage
  config.varnish_servers << { 
    :host => '0.0.0.0', :port => 6082
  }

  # Number of retries
  config.retries = 5

  # config handler (optional, if you use Hoptoad or another error tracking service)
  config.command_error_handler = lambda {|s| HoptoadNotifier.notify(s) }
end

app/controllers/application_controller.rb

class ApplicationController < ActionController::Base
  include Lacquer::CacheUtils
end

Usage

To set a custom ttl for a controller:

before_filter { |controller| controller.set_cache_ttl(15.minutes) }

Clearing the cache:

class Posts < ApplicationController
  after_filter :clear_cache, :only => [ :create, :update, :destroy ]

private

  def clear_cache
    clear_cache_for(
      root_path,
      posts_path,
      post_path(@post))
  end
end

Gotchas

The default TTL for most actions is set to 0, since for most cases you’ll probably want to be fairly explicit about what pages do get cached by varnish. The default cache header is typically

Cache-Control: max-age=0, no-cache, private

This is good for normal controller actions, since you won’t want to cache them. If TTL for an action is set to 0, it won’t mess with the default header.

The key gotcha here is that cached pages strip cookies, so if your application relies on sessions and uses authenticity tokens, the user will need a session cookie set before form actions will work. Setting default TTL to 0 here will make sure these session cookies won’t break.

As a result, all you have to do to set a cacheable action is the before filter above.

VCL config

backend default {
.host = "127.0.0.1";
.port = "8282";
.max_connections = 2000;
.connect_timeout = 600s;
.first_byte_timeout = 600s;
.between_bytes_timeout = 600s;
}

sub vcl_hash {
  ### these 2 entries are the default ones used for vcl. Below we add our own.
  set req.hash += req.url;
  set req.hash += req.http.host;

  if (req.http.cookie ~ "mobile_view=true") {
    set req.hash += "mobile";
  }
  if (req.http.user-agent ~ "(?i)palm|blackberry|nokia|phone|midp|mobi|symbian|chtml|ericsson|minimo|audiovox|motorola|samsung|telit|upg1|windows ce|ucweb|astel|plucker|x320|x240|j2me|sgh|portable|sprint|docomo|kddi|softbank|android|mmp|pdxgw|netfront|xiino|vodafone|portalmmm|sagem|mot-|sie-|ipod|up\\.b|webos|amoi|novarra|cdm|alcatel|pocket|iphone|mobileexplorer|mobile" && !(req.http.user-agent ~ "(?i)ipad") && !(req.http.cookie ~ "full_site=true")) {
    set req.hash += "mobile";
  }

  return(hash);
}

#
# Handling of requests that are received from clients.
# First decide whether or not to lookup data in the cache.
#
sub vcl_recv {
  # Pipe requests that are non-RFC2616 or CONNECT which is weird.
  if (req.request != "GET" &&
      req.request != "HEAD" &&
      req.request != "PUT" &&
      req.request != "POST" &&
      req.request != "TRACE" &&
      req.request != "OPTIONS" &&
      req.request != "DELETE") {
    return(pipe);
  }

  # Pass requests that are not GET or HEAD
  if (req.request != "GET" && req.request != "HEAD") {
    return(pass);
  }

  # Pass requests for blog pages greater than page 3
  if (req.url ~ "page=([4-9]|[1-9][0-9]+)$") {
    return(pass);
  }

  # Pass requests that we know we aren't caching
  if (req.url ~ "^/admin") {
    return(pass);
  }

  if (req.url ~ "\/private\/") {
    return(pass);
  }

  #
  # Everything below here should be cached
  #

  # Handle compression correctly. Varnish treats headers literally, not
  # semantically. So it is very well possible that there are cache misses
  # because the headers sent by different browsers aren't the same.
  # @see: http://varnish.projects.linpro.no/wiki/FAQ/Compression
  if (req.http.Accept-Encoding) {
    if (req.http.Accept-Encoding ~ "gzip") {
      # if the browser supports it, we'll use gzip
      set req.http.Accept-Encoding = "gzip";
    } elsif (req.http.Accept-Encoding ~ "deflate") {
      # next, try deflate if it is supported
      set req.http.Accept-Encoding = "deflate";
    } else {
      # unknown algorithm. Probably junk, remove it
      remove req.http.Accept-Encoding;
    }
  }

  # Set grace time, lookup in the cache
  set req.grace = 1s;
  return(lookup);
}

#
# Called when entering pipe mode
#  
sub vcl_pipe {
  # If we don't set the Connection: close header, any following
  # requests from the client will also be piped through and
  # left untouched by varnish. We don't want that.
  set req.http.connection = "close";
  return(pipe);
}

#
# Called when the requested object has been retrieved from the
# backend, or the request to the backend has failed
#
sub vcl_fetch {
  esi;
  # Do not cache the object if the backend application does not want us to.
  if (beresp.http.Cache-Control ~ "(no-cache|no-store|private|must-revalidate)") {
    return(pass);
  }

  # Do not cache the object if the status is not in the 200s
  if (beresp.status >= 300) {
    return(pass);
  }

  #
  # Everything below here should be cached
  #
  if (req.url ~ "\/posts\/comments") {
    set beresp.ttl = 0s;
  }

  # Remove the Set-Cookie header
  remove beresp.http.Set-Cookie;

  # Set the grace time
  set beresp.grace = 1s;

  if (req.url ~ "\.(css|js|jpg|jpeg|gif|ico|png)\??\d*$") {
    /* Remove Expires from backend, it's not long enough */
    unset beresp.http.expires;

    /* Set the clients TTL on this object */
    set beresp.http.cache-control = "public, max-age=31536000";

    /* marker for vcl_deliver to reset Age: */
    set beresp.http.magicmarker = "1";
  } else {
    set beresp.http.Cache-Control = "private, max-age=0, must-revalidate";
    set beresp.http.Pragma = "no-cache";
  }

  # return(deliver); the object
  return(deliver);
}

sub vcl_deliver {
  if (resp.http.magicmarker) {
    /* Remove the magic marker */
    unset resp.http.magicmarker;

    /* By definition we have a fresh object */
    set resp.http.age = "0";
  }   

  # Add a header to indicate a cache HIT/MISS
  if (obj.hits > 0) {
    set resp.http.X-Cache = "HIT";
  } else {
    set resp.http.X-Cache = "MISS";
  }
}

Note on Patches/Pull Requests