• Check_MK, software updates and mount options alarms

    We have been using nagios (more specifically Check_MK) recently at work to get some monitoring information on our CentOS instances. Recently we decided to reprovision all of our EC2 instances to apply several security upgrades. Among the packages upgraded, there was the kernel (which I guess was the cause of our subsequent problems).

    After updating all our instances, nagios began to complain about the mount options no being the right ones for the root file system, and started sending critical alarms. The file system was ok, it was mounted without problems and everything was woking fine, but for some reason the mount options had changed after the reprovisioning.

    Turns out that Check_MK checks the options in place when it does the initial inventory, and if the options change over time, it issues an alarm. If you face this problem, just do a reinventory of your machines and reload the configuration and restart the service, and it should be fine:

    cmk -II && cmk -R
  • ARM assembler in Raspberry Pi – Chapter 14

    In chapter 13 we saw the basic elements of VFPv2, the floating point subarchitecture of ARMv6. In this chapter we will implement a floating point matrix multiply using VFPv2.

    Read on →

  • ARM assembler in Raspberry Pi – Chapter 13

    So far, all examples have dealt with integer values. But processors would be rather limited if they were only able to work with integer values. Fortunately they can work with floating point numbers. In this chapter we will see how we can use the floating point facilities of our Raspberry Pi.

    Read on →

  • Capybara, pop up windows and the new PayPal sandbox

    This past weeks we have been doing a massive refactoring of our testing suite at work to set up a nice CI server setup, proper factories, etc. Our tool-belt so far is basically a well known list of Rails gems:

    For the CI server we decided to use a third party SaaS as our dev team is small and we don’t have the manpower nor the time to set it up ourselves, and we went for CircleCI, which has given us good results so far (easy to set up, in fact almost works out of the box without having to do anything, it has a good integration with GitHub, it’s reasonably fast, and the guys are continuously improving it and very receptive to client’s feedback).

    Back to the post topic, when refactoring the integration tests, we discovered that PayPal decided recently to change the way their development sandbox works, and the tests we had in place broke because of it.

    The basic workflow when having to test with PayPal involves a series of steps:

    • Visit their sandbox page and log in with your testing credentials. This saves a cookie in the browser.
    • Go back to your test page and do the steps needed to perform a payment using PayPal.
    • Authenticate again to PayPal with your test buyers account and pay.
    • Catch the PayPal response and do whatever you need to finish your test.

    With the old PayPal sandbox, the login was pretty straightforward as you only needed to find the username and password fields in the login form of the sandbox page, fill them in, click the login button, and that was all. But with the new version it’s not that easy. The new sandbox has no login form at the main page. It has a login button which you have to click, then a popup window is shown with the login form. In there you have to input your credentials and click on the login button. Then this popup window does some server side magic, closes itself and triggers a reload on the main page, which will finally show you as logged in.

    There’s probably a POST request that you can automatically do to simplify all this, but PayPal is not known as developer documentation friendly so I couldn’t find it. As a result, we had to modify our Capybara tests to handle this new scenario. As we’ve never worked with pop up windows before I thought it’d be nice to share how we did it in case you need to do something similar.

    The basic workflow is as follows:

    • Open the main PayPal sandbox window.
    • Click on the login button.
    • Find the new popup window.
    • Fill in the form in that new window.
    • Go back to your main window.
    • Continue with your usual testing.

    This assumes you are using the Selenium driver for Capybara. Here’s the code we used to get this done:

    describe "a paypal express transaction", :js => true do
      it "should just work" do
        # Visit the PayPal sandbox url
        visit "https://developer.paypal.com/"
        # The link for the login button has no id...
        find(:xpath, "//a[contains(@class,'ppLogin_internal cleanslate scTrack:ppAccess-login ppAccessBtn')]").click
        # Here we have to use the driver to find the newly opened window using it's name
        # We also get the reference to the main window as later on we'll have to go back to it
        login_window = page.driver.find_window('PPA_identity_window')
        main_window = page.driver.find_window('')
        # We use this to execute the next instructions in the popup window
        page.within_window(login_window) do
          #Normally fill in the form and log in
          fill_in 'email', :with => "<your paypal sandbox username>"
          fill_in 'password', :with => "<your paypal sandbox password>"
          click_button 'Log In'
        #More on this sleep later
        #Switch back to the main window and do the rest of the test in it
        page.within_window(main_window) do
          #Here goes the rest of your test

    Now there is an important thing to note on the code above: the sleep(30) call. By now you may have read on hundreds of places that using sleep is not a good practice and that your tests should not rely on that. And that’s true. However, PayPal does a weird thing and this is the only way I could use to make the tests pass. It turns out that after clicking the Log In button, the system does some behind the curtains magic, and after having done that, the popup window closes itself and then triggers a reload on the main page. This reload triggering makes things difficult. If you instruct Capybara to visit your page right after clicking the Log In button, you risk having that reload trigger fired in between, and then your test will fail because the next selector you use will not be found as the browser will be in the PayPal sandbox page.

    There are probably better and more elegant ways to get around this. Maybe place a code to re-trigger your original visit if it detects you are still on the PayPal page, etc. Feel free to use the comments to suggest possible solutions to that particular problem.

  • ARM assembler in Raspberry Pi – Chapter 12

    We saw in chapter 6 some simple schemes to implement usual structured programming constructs like if-then-else and loops. In this chapter we will revisit these constructs and exploit a feature of the ARM instruction set that we have not learnt yet.

    Read on →