Setting up Varnish on Drupal 7 on Debian

apt-get install varnish

Install and activate  varnish module
https://drupal.org/project/varnish

nano /etc/default/varnish

Repace the default config with this

# Configuration file for varnish
#
# /etc/init.d/varnish expects the variables $DAEMON_OPTS, $NFILES and $MEMLOCK
# to be set from this shell script fragment.
#
# Note: If systemd is installed, this file is obsolete and ignored.  You will
# need to copy /lib/systemd/system/varnish.service to /etc/systemd/system/ and
# edit that file.
# Should we start varnishd at boot?  Set to "no" to disable.
START=yes
# Maximum number of open files (for ulimit -n)
NFILES=131072
# Maximum locked memory size (for ulimit -l)
# Used for locking the shared memory log in memory.  If you increase log size,
# you need to increase this number as well
MEMLOCK=82000
# Default varnish instance name is the local nodename.  Can be overridden with
# the -n switch, to have more instances on a single server.
# INSTANCE=$(uname -n)
# This file contains 4 alternatives, please use only one.

## Alternative 4, Do It Yourself
#Dervice from:
#http://www.lullabot.com/blog/article/configuring-varnish-high-availability-multiple-web-servers
# DAEMON_OPTS=""
DAEMON_OPTS="-a :80,:443 \
             -T localhost:6082 \
             -f /etc/varnish/default.vcl \
             -u varnish -g varnish \
             -S /etc/varnish/secret \
             -p thread_pool_add_delay=2 \
             -p thread_pools=8  \
             -p thread_pool_min=100 \
             -p thread_pool_max=4000 \
             -p session_linger=50 \
             -p sess_workspace=262144 \
             -s malloc,3G"

Now down to default.vcl

nano /etc/varnish/default.vcl

Dont't forget to chagne acl internal IP below:

# This is a basic VCL configuration file for varnish. See the vcl(7) main page for details on VCL syntax and semantics.
#
# Default backend definition. Set this to point to your content server.
#
 backend default {
     .host = "127.0.0.1";
     .port = "8080";
     .connect_timeout = 600s;
     .first_byte_timeout = 600s;
     .between_bytes_timeout = 600s;
 }
acl internal {
#  "192.10.0.0"/24;
#CHANGE THIS
"1.2.3.4";
}


# Respond to incoming requests.
sub vcl_recv {
  if (req.request == "GET" && req.url ~ "^/varnishcheck$") {
    error 200 "Varnish is Ready";
  }
  # Allow the backend to serve up stale content if it is responding slowly.
  if (!req.backend.healthy) {
    # Use anonymous, cached pages if all backends are down.
    unset req.http.Cookie;
    if (req.http.X-Forwarded-Proto == "https") {
      set req.http.X-Forwarded-Proto = "http";
    }
    set req.grace = 30m;
  } else {
    set req.grace = 15s;
  }
  # Get ride of progress.js query params
  if (req.url ~ "^/misc/progress\.js\?[0-9]+$") {
    set req.url = "/misc/progress.js";
  }
  # If global redirect is on
  #if (req.url ~ "node\?page=[0-9]+$") {
  #  set req.url = regsub(req.url, "node(\?page=[0-9]+$)", "\1");
  #  return (lookup);
  #}
  # Do not cache these paths.
  if (req.url ~ "^/status\.php$" ||
      req.url ~ "^/update\.php$" ||
      req.url ~ "^/ooyala/ping$" ||
      req.url ~ "^/admin" ||
      req.url ~ "^/admin/.*$" ||
      req.url ~ "^/user" ||
      req.url ~ "^/user/.*$" ||
      req.url ~ "^/users/.*$" ||
      req.url ~ "^/info/.*$" ||
      req.url ~ "^/flag/.*$" ||
      req.url ~ "^.*/ajax/.*$" ||
      req.url ~ "^.*/ahah/.*$") {
    return (pass);
  }
  # Pipe these paths directly to Apache for streaming.
  if (req.url ~ "^/admin/content/backup_migrate/export") {
    return (pipe);
  }
  # Do not allow outside access to cron.php or install.php.
  if (req.url ~ "^/(cron|install)\.php$" && !client.ip ~ internal) {
    # Have Varnish throw the error directly.
    error 404 "Page not found.";
    # Use a custom error page that you've defined in Drupal at the path "404".
    # set req.url = "/404";
  }
  # Handle compression correctly. Different browsers send different
  # "Accept-Encoding" headers, even though they mostly all support the same
  # compression mechanisms. By consolidating these compression headers into
  # a consistent format, we can reduce the size of the cache and get more hits.=
  # @see: http:// varnish.projects.linpro.no/wiki/FAQ/Compression
  if (req.http.Accept-Encoding) {
    if (req.http.Accept-Encoding ~ "gzip") {
      # If the browser supports it, we'll use gzip.
      set req.http.Accept-Encoding = "gzip";
    }
    else if (req.http.Accept-Encoding ~ "deflate") {
      # Next, try deflate if it is supported.
      set req.http.Accept-Encoding = "deflate";
    }
    else {
      # Unknown algorithm. Remove it and send unencoded.
      unset req.http.Accept-Encoding;
    }
  }
  # Always cache the following file types for all users.
  if (req.url ~ "(?i)\.(png|gif|jpeg|jpg|ico|swf|css|js)(\?[a-z0-9]+)?$") {
    unset req.http.Cookie;
  }
  # Remove all cookies that Drupal doesn't need to know about. ANY remaining
  # cookie will cause the request to pass-through to a backend. For the most part
  # we always set the NO_CACHE cookie after any POST request, disabling the
  # Varnish cache temporarily. The session cookie allows all authenticated users
  # to pass through as long as they're logged in.
  #
  # 1. Append a semi-colon to the front of the cookie string.
  # 2. Remove all spaces that appear after semi-colons.
  # 3. Match the cookies we want to keep, adding the space we removed
  #    previously, back. (\1) is first matching group in the regsuball.
  # 4. Remove all other cookies, identifying them by the fact that they have
  #    no space after the preceding semi-colon.
  # 5. Remove all spaces and semi-colons from the beginning and end of the
  #    cookie string.
  if (req.http.Cookie) {
    set req.http.Cookie = ";" + req.http.Cookie;
    set req.http.Cookie = regsuball(req.http.Cookie, "; +", ";");
    set req.http.Cookie = regsuball(req.http.Cookie, ";(S{1,2}ESS[a-z0-9]+|NO_CACHE)=", "; \1=");
    set req.http.Cookie = regsuball(req.http.Cookie, ";[^ ][^;]*", "");
    set req.http.Cookie = regsuball(req.http.Cookie, "^[; ]+|[; ]+$", "");
    if (req.http.Cookie == "") {
      # If there are no remaining cookies, remove the cookie header. If there
      # aren't any cookie headers, Varnish's default behavior will be to cache
      # the page.
      unset req.http.Cookie;
    }
    else {
      # If there is any cookies left (a session or NO_CACHE cookie), do not
      # cache the page. Pass it on to Apache directly.
      return (pass);
    }
  }
  ## From default below ##
  if (req.restarts == 0) {
    if (req.http.x-forwarded-for) {
      set req.http.X-Forwarded-For =
      req.http.X-Forwarded-For + ", " + client.ip;
    } else {
      set req.http.X-Forwarded-For = client.ip;
    }
  }
  if (req.request != "GET" &&
    req.request != "HEAD" &&
    req.request != "PUT" &&
    req.request != "POST" &&
    req.request != "TRACE" &&
    req.request != "OPTIONS" &&
    req.request != "DELETE") {
      /* Non-RFC2616 or CONNECT which is weird. */
      return (pipe);
  }
  if (req.request != "GET" && req.request != "HEAD") {
      /* We only deal with GET and HEAD by default */
      return (pass);
  }
  ## Unset Authorization header if it has the correct details...
  #if (req.http.Authorization == "Basic ") {
  #  unset req.http.Authorization;
  #}
  if (req.http.Authorization || req.http.Cookie) {
      /* Not cacheable by default */
      return (pass);
  }
  return (lookup);
}
# Code determining what to do when serving items from the Apache servers.
sub vcl_fetch {
  # Don't allow static files to set cookies.
  if (req.url ~ "(?i)\.(png|gif|jpeg|jpg|ico|swf|css|js)(\?[a-z0-9]+)?$") {
    # beresp == Back-end response from the web server.
    unset beresp.http.set-cookie;
  }
  else if (beresp.http.Cache-Control) {
    unset beresp.http.Expires;
  }
  if (beresp.status == 301) {
    set beresp.ttl = 1h;
    return(deliver);
  }
  ## Doesn't seem to work as expected
  #if (beresp.status == 500) {
  #  set beresp.saintmode = 10s;
  #  return(restart);
  #}
  # Allow items to be stale if needed.
  set beresp.grace = 1h;
}
# Set a header to track a cache HIT/MISS.
sub vcl_deliver {
  if (obj.hits > 0) {
    set resp.http.X-Varnish-Cache = "HIT";
  }
  else {
    set resp.http.X-Varnish-Cache = "MISS";
  }
}
# In the event of an error, show friendlier messages.
sub vcl_error {
     set obj.http.Content-Type = "text/html; charset=utf-8";
     set obj.http.Retry-After = "5";
     synthetic {"
<?xml version="1.0" encoding="utf-8"?>
<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Strict//EN"
  "http://www.w3.org/TR/xhtml1/DTD/xhtml1-strict.dtd">
<html>
   <head>
     <title>"} + obj.status + " " + obj.response + {"</title>
   </head>
   <body>
     <h1>Error "} + obj.status + " " + obj.response + {"</h1>
     <p>"} + obj.response + {"</p>
     <h3>Guru Meditation:</h3>
     <p>XID: "} + req.xid + {"</p>
     <hr>
     <p>Varnish cache server</p>
   </body>
</html>
"};
     return (deliver);
}

service varnish restart

Test if it works:
http://www.isvarnishworking.com/

You can also install this Perl lib to check varnish locally:

sudo apt-get install libwww-perl && GET -Used http://localhost:6081/index.html







Sources:

Handy:

http://andrewdunkle.com/2012/installing-varnish-for-drupal-7.html

More in-depth:

http://www.lullabot.com/blog/article/configuring-varnish-high-availability-multiple-web-servers