Friday, 23 November 2012

Linux driver file (PPD) for Fuji Xerox printers

The cheapskates at FX don't provide PPDs for Linux, even though they are the same as the MacOS files.

Now, opening apple's *.dmg files is surprisingly convoluted.  Here's a step-by-step guide to, hopefully, save you some time.

1. Download the MacOS ApeosPort IV drivers from Fuji Xerox's site.
2. Download dmg2img (I downloaded the source code for dmg2img and ran `make' - you guys rock!).
3. Convert the dmg file into an image:

./dmg2img ~/Downloads/fxmacprnps1208am105iml.dmg /tmp/out.img

4. Mount the obtained image:

sudo mount  -o loop /tmp/out.img /mnt/iso/

5. Use xar (yum install xar) to extract the pkg file:

cp /mnt/iso/Fuji\ Xerox\ PS\ Plug-in\ Installer.pkg /tmp/
cd /tmp && mkdir fx && cd fx
xar -xf ../Fuji\ Xerox\ PS\ Plug-in\ Installer.pkg 

6. Inside the extracted folders, locate and copy the Payload file with the PPDs:

cp ppd.pkg/Payload /tmp/Payload.cpio.gz

7. Gunzip the file and extract the cpio archive:

cd /tmp
gunzip Payload.cpio.gz
mkdir ppd && cd /tmp/ppd
cpio -id < ../Payload.cpio

8. VoilĂ ! your PPD files are in Library/Printers/PPDs/Contents/Resources/:

Fuji Xerox 4112 PS.gz          FX ApeosPort-IV C4475 PS.gz     FX DocuCentre-IV 7080 PS.gz
Fuji Xerox 4127 PS.gz          FX ApeosPort-IV C5570 PS.gz     FX DocuCentre-IV C2260 PS.gz
Fuji Xerox D110 PS.gz          FX ApeosPort-IV C5575 PS.gz     FX DocuCentre-IV C2263 PS.gz
Fuji Xerox D125 PS.gz          FX ApeosPort-IV C5580 PS.gz     FX DocuCentre-IV C2265 PS.gz
Fuji Xerox D95 PS.gz           FX ApeosPort-IV C6680 PS.gz     FX DocuCentre-IV C2270 PS.gz
FX ApeosPort 350 I  PS B.gz    FX ApeosPort-IV C7780 PS.gz     FX DocuCentre-IV C2275 PS.gz
FX ApeosPort 350 I  PS.gz      FX DocuCentre 450 I  PS B.gz    FX DocuCentre-IV C3370 PS.gz


Thursday, 8 November 2012

Caching 301 redirects in Varnish while keeping the protocol

I have noticed a drop in our Varnish cache hit ratio and, upon investigation, found that the backend was not allowing 301 redirects to be cached:

Client request:
   42 RxRequest    c GET
   42 RxURL        c /img_resized/au/images/gifts/2012/hero/christmas-homepage-hero-alyce.jpg
   42 RxProtocol   c HTTP/1.1

Backend request: 
   21 TxRequest    b GET
   21 TxURL        b /img_resized/au/images/gifts/2012/hero/christmas-homepage-hero-alyce.jpg
   21 TxProtocol   b HTTP/1.1

Backend response: 
   21 RxHeader     b Cache-Control: no-cache
   21 RxHeader     b Location:
   21 RxHeader     b Status: 301

I logged a bug for the application to be fixed and, in the meantime, added a VCL snippet to override the backend headers:

        # WSF-xxxx: App is not allowing redirects to be cached
        if ((req.http.Host == "") &&
           (beresp.status == 301) &&
           (beresp.http.Cache-Control ~ "no-cache")) {
                set beresp.http.Cache-Control = "public, max-age=604800";

There's a catch though.  We do SSL offloading for in our F5 BigIP LTM load balancer.  In other words, the load balancer receives a https request and, in turn, makes a http request to Varnish.

As Varnish doesn't support SSL natively it is unaware of the protocol (http or https) being used; thus, the requests below get cached with the first answer it sees:

HTTP request
curl -I
HTTP/1.1 301 Moved Permanently

HTTPS request
curl -I
HTTP/1.1 301 Moved Permanently

Notice that the HTTPS request was redirected to a HTTP URL.  This will most certainly cause issues, including mixed-mode SSL alerts in some browsers.

Our backend is a Ruby on Rails application and, to my surprise, it understands the X-Forwarded-Proto HTTP header.  This means that the application will use the value of X-Forwarded-Proto to build the URL in the Location header.

I improved the F5 iRule by instructing the load balancer to insert a X-Forwarded-Proto header in HTTPS requests which were being off-loaded to Varnish:

      HTTP::header replace X-Forwarded-Proto "https"

In addition to this, I also had to instruct Varnish to use the X-Forwarded-Proto header in the cache hash:

sub vcl_hash {
if (req.http.X-Forwarded-Proto) {
set req.hash += req.http.X-Forwarded-Proto;

With these tweaks Varnish is now able to account for SSL offloading and correctly serve the appropriate cached version of a page.  An improvement on this configuration would be to only use X-Forwarded-Proto in the hash if the response is a redirect; at the moment I can't be bothered that Varnish is caching objects twice.

HTTP request
$curl -I
HTTP/1.1 301 Moved Permanently

HTTPS request
$curl -I
HTTP/1.1 301 Moved Permanently

Saturday, 10 March 2012

Using varnish to increase the cache time of slow pages

If you are having trouble getting your organisation to accept performance as a feature, one solution is to tie it to another feature.

A common discussion between content owners ("the business") and web operators is how long to cache pages for.  The content owners want to see their fresh content in minimal time but web operators want to cache expensive (to generate) content longer.

Usually content owners get their way, as they should, or you wouldn't have a business.  So you set the default cache time on all pages to something low, like 10 minutes.  If you are not quite ready to take the ESI leap, an attractive compromise is to penalise only expensive pages with a higher expiry time.

If your server backend runs on Ruby-On-Rails, the job is already half-done since requests return a X-Runtime HTTP header indicating, in milliseconds, how long it took RoR to generate the page.  This header is either available in most web frameworks or would be quite easy to implement.

We use the VCL code below to override the internal varnish TTL for slow-to-generate pages.

# VCL 2.1.5 to extend TTL on pages which take 1s or longer to generate
if (beresp.http.X-Runtime ~ "[0-9]{4,}") {
    if (beresp.ttl < 1d) {
        set beresp.ttl = 1d;
        set beresp.http.X-Cache-Override = "1d";

We choose not to modify the original headers, which are sent to the client, because this gives you the opportunity to keep or ban the content from Varnish while letting the browsers come back to ask for the "new" content.

The code also sets a "X-Cache-Override" header so you can tell which pages are taking 1 second or more to generate.

This is great because now, when someone complains that their content isn’t refreshing, we can improve performance to areas of the site that matter to the business instead of the whole “make the site faster” approach.

The results will come quickly.  Two days after putting this in production Google has shown that the average page load time in our (very large) site dropped half a second. As you can see in the graph below, the trend is still going down (click on the image).
Site speed improvement as perceived by the Google bot

A further improvement to this would be to write an algorithm which sets the TTL based on the page generation time.  For example, add 1 day to the TTL for each second it takes the page to generate so if a page takes 5 seconds to generate, keep it for 5 days.