php-webdriver bindings for selenium: how to add time-outs

Not all webpages finish loading. In particular I've a page that keeps streaming data back to the client, and never finishes. (For instance it might be used from an ajax call.) I want to test this from Selenium, but have been hitting problems. The main problem is Selenium's get() function, which is used to fetch a fresh URL, does not return until the page has finished loading [1]. In my case that meant never, and so my test script locked up!

However all is not lost; you can specify a page load timeout. It is hidden in the protocol docs, but I've added it to the php webdriver library I use (v0.9). See the three functions below [2]; just paste them in to the bottom of WebDriver.php.

I also needed one bug fix in WebDriver.php's public function get($url). It currently ends with:
    $response=curl_exec($session);

Just after that line you should add this:
    return $this->extractValueFromJsonResponse($response);


The time-out, and that bug fix, can be used like this:

require_once "/usr/local/src/selenium/php-webdriver-bindings-0.9.0/phpwebdriver/WebDriver.php";
$webdriver = new WebDriver("localhost", "4444");
$webdriver->connect("firefox");
$webdriver->setPageLoadTimeout(2000);   //2 seconds
$url="http://example.com/forever.php"; //A page that never finishes loading
$obj=$webdriver->get($url);
if($obj===null){
    $current_url=$webdriver->getCurrentUrl();
    if(!$current_url){
        //Selenium-server not running
        }
    else{
        //It worked! (it completed loading in under two seconds)
        }
    }
elseif($obj->class=='org.openqa.selenium.TimeoutException'){
    //It timed out
    }
elseif($obj->class=='org.openqa.selenium.remote.UnreachableBrowserException'){
    //Browser was closed (or selenium-server was shutdown)
    }
else{
    echo "FAILED:";print_r($obj);
    }

This is useful stuff. There is still one problem left for me: I wanted to load two seconds worth of data and then look at it. But I cannot. The browser refuses to listen to selenium while it is loading a page! So though get() returned control to my script after two seconds, I cannot do anything with that control (except close the browser window), because the URL is still actually loading. And it will do that forever!!  (I've played with an interesting alternative approach, which also fails, but suggests that a solution is possible. But that is out of the scope of this post, which is to show how to add the time limit functions to php-webdriver-bindings.)

[1]: This is browser-specific behaviour, not by Selenium design. Firefox and Chrome, at least, behave this way.


[2]: Consider this code released, with no warranty, under the MIT license, and permission granted to use in the php-webdriver-bindings project with no attribution required.

    /**
     * Set wait for a page to load.
     *
     * This timeout is for the get() function. (Firefox and Chrome, at least, won't return from get()
     * until a page is fully loaded.  If remote server is streaming content, they would never return
     * without this time-out.)
     *
     * @param Number $timeout Number of milliseconds to wait.
     * @author Darren Cook, 2012
     * @internal http://code.google.com/p/selenium/wiki/JsonWireProtocol#/session/:sessionId/timeouts
     */
    public function setPageLoadTimeout($timeout) {
        $request = $this->requestURL . "/timeouts";       
        $session = $this->curlInit($request);
        $args = array('type'=>'page load', 'ms' => $timeout);
        $jsonData = json_encode($args);
        $this->preparePOST($session, $jsonData);
        curl_exec($session);       
    }

    /**
     * Set wait for a script to finish.
     *
     * @param Number $timeout Number of milliseconds to wait.
     * @author Darren Cook, 2012
     * @internal http://code.google.com/p/selenium/wiki/JsonWireProtocol#/session/:sessionId/timeouts
     */
    public function setAsyncScriptTimeout($timeout) {
        $request = $this->requestURL . "/timeouts";       
        $session = $this->curlInit($request);
        $args = array('type'=>'script', 'ms' => $timeout);
        $jsonData = json_encode($args);
        $this->preparePOST($session, $jsonData);
        curl_exec($session);       
    }
    /**
     * Set implict wait.
     *
     * This is for waiting for page elements to appear. Not useful for scripts or
     * waiting for the initial get() call to time out.
     *
     * @param Number $timeout Number of milliseconds to wait.
     * @author Darren Cook, 2012
     * @internal http://code.google.com/p/selenium/wiki/JsonWireProtocol#/session/:sessionId/timeouts
     */
    public function setImplicitWaitTimeout($timeout) {
        $request = $this->requestURL . "/timeouts";       
        $session = $this->curlInit($request);
        $args = array('type'=>'implicit', 'ms' => $timeout);
        $jsonData = json_encode($args);
        $this->preparePOST($session, $jsonData);
        curl_exec($session);       
    }

EC2 and Windows: a match made in... Hell

Henry Ford is famous for his lack of flexibility over the Model T: You can it in any colour you want, as long as it is black.

I think Amazon have taken a leaf out if his book, when offering their Windows instances: You can have any size disk you want, as long as it is 30Gb.

Don't believe me? Go on, try automating the creation of a 100Gb boot disk Windows machine. Or creating one from the web interface, without any post-configuration steps in Windows itself.

(I'll save you the Google: here is the AWS engineers telling you the multiple steps needed to achieve that. The instructions are different depending on the exact version of Windows.)

In fact, try automating anything to do with Windows configuration, using EC2. You can't. It can't be, won't be, scripted. You always have to log on afterwards (going through the EC2 Console to get your almost-impossible-to-type password) to do something. Usually quite a tedious and time-consuming something.
The bottom-line: Windows is not designed for the cloud.



...and yet, some of my clients, and some of my potential clients, insist on trying to use Windows anyway. The cloud is where they feel they should be, so people want to move their legacy apps there. Whenever I ask them how they do it, or why they do it, they seem to find justification. It is the cloud, look we're scaling. We're faster. It works! Like a man let out of prison, and running free in the meadow... only he still has the manacles and chains from his time doing time. Am I carrying my metaphor too far by wishing people would stop and take the Linux axe to the manacles before rushing off to the meadow?

Are you an expert at automating Windows on EC2? Please post a comment showing off your knowledge. I'm willing to learn, and will edit this article if you convince me it can be done :-)

Cloud options compared: EC2, Rackspace, HP

I've been participating in HP Cloud's closed beta program, and they have now announced their billing They use the same cloud system and API as Rackspace, making it a fair comparison.  (See Rackspace cloud server pricing and Rackspace cloud file pricing)

Executive summary: HP have priced themselves slightly lower, but don't have the two smallest server configurations. So, Rackspace is still better than HP or Amazon EC2 if you just need something minimal, as I described here.
(2012-08-15 UPDATE: Rackspace are stopping their minimal server config: no more 256MB option in their "nextgen" V2 API. Also scheduled images are not available in the V2 API (yet).)

HP offer slightly less disk space than Rackspace, for the same memory size. HP's bandwidth is slightly cheaper than Rackspace; incoming bandwidth is free on both.

HP's CDN offering is weird; based on your billing location, rather than where your servers are, or where your customers are! If you are a U.S. or European company it is cheaper. If not it is more expensive. However, for Japan, HK, Singapore it is only a fraction more expensive, so not a showstopper. Also it is tiered: if you're spending more than $200/month on CDN bandwidth it will work out cheaper still.
If your headquarters are not in North America, Europe, Latin America, Japan, Hong Kong or Singapore then HP pricing says they'd rather you took your CDN business elsewhere.

( 2012-06-12 UPDATE:  I've added a surprise Linux cloud hosting option to the below: Microsoft Azure! They are competitive at the low end: 1GHz CPU, 768MB RAM, 25GB storage, 4GB outbound bandwidth (inbound is free), is $12.51/month (about 1.5c/hr). An extra 20% discount for paying for 6 months. But also reasonable at the high-end too (except 14GB is the most memory they can offer). (price calculator) )


Comparing HP's cheapest option to the closest (based on memory size) alternative:
HP: 1Gb RAM, 30GB disk, 1 virtual core: $0.04/hr ($29/month)
Rackspace: 1Gb RAM, 40GB disk, 1/16th of a 4-CPU server: $0.06/hr ($43.80/month)
EC2 Small: 1.7GB RAM, 160GB disk, 1 virtual core, $0.08/hr ($58/month)
Azure Small: 1.6GHz CPU, 1.75GB RAM, 25GB disk, $0.08/hr ($60/month)
   (NB. the XSmall, with 768MB RAM, 1Ghz CPU is $12.50/month)

At the top of the CPU range:
HP: 32GB RAM, 960GB disk, 8 virtual cores: $1.28/hr  ($934/month)
Rackspace: 31GB RAM, 1200GB disk,  4-CPUs: $1.80/hr ($1,314/month)
EC2, High-CPU Extra Large:7GB RAM, 1690GB disk, 8 virtual cores (20 compute units): $0.66/hr ($481/month)
EC2, High-Memory Quadruple Extra Large: 68GB RAM, 1690GB disk, 8 virtual cores (26 compute units): $1.80/hr ($1,314/month)
Azure, XLarge: 8 x 1.6GHz CPU, 14GB RAM, 975GB disk: $0.64/hr ($575/month)

(So, if you are CPU bound then Amazon is best, if memory bound then HP is best.)

Overall, the pricing seems reasonable. However Rackspace have a brand oozing stability and reliability, and Amazon are huge and have data centres all over the world, so I'm not sure HP prices are low enough to worry their competitors. The 50% discount during the beta program makes them a good buy, short-term, though!

Changing Rackspace Cloud Instance Sizes

Following on from my post about the actual costs of using Rackspace, this article is about the "Actual downtime of changing the size of a Rackspace cloud server".

I wanted to go from a 10Gb disk to 20Gb disk. I got confused by the interface and accidentally went from 10Gb to 40Gb. So I then also got to try downsizing from 40Gb to 20Gb!

Q1. Does my IP address change? Do I need a new SSH key?
A. No and No.

Q2. How long does it take?
A. The 40Gb to 20Gb downsize took 13 minutes in total. The 10Gb to 40Gb upsize was about the same or slightly quicker. If you like to be careful and take a disk image beforehand, that takes about another 10-15 minutes (for about 9Gb, so allow more if your disk is bigger).

Q3. How much downtime?
A. At least 30 seconds... Prior to the move I saw activity in one program at 06:28:27; the new server was fully running at 06:29:05-ish, and the first new activity in that program was at 06:30:03.

The reason for the almost 60 second delay in that particular program was it gets started from a monitoring script (that I wrote) that runs on a 1-minute cronjob. The cron job didn't run at 06:29:00, so had to wait until 06:30:00. If I had started my program from the init.d scripts, or even from rc.local, the downtime would only have been 30-40 seconds. That is the same downtime you can expect for a webserver.

Q4. Does it depend on the size of the server?
A. I believe so. Bigger servers would have more files to copy.

Q5. Do in-memory caches survive? Do background processes keep running?
A. No and no. The resize implies a reboot. Any background process you'd started manually before needs restarting manually again when the new server comes up. Use /etc/rc.local or cronjobs to auto-start things.

Q6. Do I need to be around when I resize?
A. Yes to get it started. You could then go away (you are supposed to verify it when it comes up, but I think if you don't verify it then after a few hours it assumes you are happy that everything is running smoothly.)  (The point of the verify step is they keep the old image around and can quickly revert - I did not test this to see how quick the revert would be.)

Q7. How do I change server size without any downtime at all?
A. Big question. The glib answer is: If you have to ask, then it is too difficult. The slightly more helpful answer is: if a web server then run two servers, with a load balancer in front of them; if a database server, look into database clusters.