Dec 12, 2016

Web Application Hosting with Heroku

I know Ruby but have little experience with web apps. If you're like me then this article could be useful.

I needed a way to browse API documentation of multiple related code repositories. (Yes, it's YaST).

I made a tool for that in the form of a web application. This was really easy with the Sinatra framework.

First I ran it locally on my machine for myself. Then I ran it on a machine in the company network for team mates to use. It was a VM that I repurposed from a previous experiment. Then Pepa said it would be nice to have it publicly accessible. How hard could that be?

I had heard that Heroku makes that sort of thing easy, and it turned to be true!

  1. It's free. A low profile app, that only needs to run occasionally, fits into their Free service plan. It sleeps after 30 minutes and takes 10 seconds to wake up.

  2. Easy to sign up. Enter your e-mail, pick a password. No other details required.

  3. Easy app creation: pick the region (US or EU). Optionally pick a name (I got salty-waters-71436 for my demo app).

  4. Easy to set up the tooling. Well, they install the curl | bash way. Over https. And then the downloaded code downloads some more.

    If you want to start small, the setup by hand is easy too, now download required:

    touch ~/.netrc
    chmod 600 ~/.netrc
    echo "machine login YOUR_EMAIL password ffffffff-ffff-ffff-ffff-ffffffffffff" >> ~/.netrc

    Where the hex string is your API Key (Top-right Person icon > Account Setings > scroll down)

Now let's write a trivial web app.

  1. Make a git repo.
  2. Make a two-line Sinatra app.

    require "sinatra"
    get "/" { "Hello, world!" }
  3. Add a two-line Gemfile declaration; add also Gemfile.lock to Git.

    source ""
    gem "sinatra", "~> 1.4.0"
  4. Add a oneliner Procfile.

    web: bundle exec ./timeserver

    (This was new to me. It's not needed locally but needed for Heroku, and anyway useful once you outgrow oneliners. Use foreman start to use it)

  5. Use your app name as the remote repo name. Push to deploy (or set up automatic deployment):

    git remote add heroku
    git push heroku

That's it! See the app in action:

To see my actual app, instead of the trivial demo built for this blog post, go to

Aug 1, 2016

Virtual Machine from a Hard Disk Image with virt-install --import

This is one of many ways to create a virtual machine. This way starts with a hard disk image.

wget -O /var/lib/libvirt/images/$NAME $IMG
virt-install --name $NAME \
       --ram 2048 --graphics type=vnc \
       --network bridge=br0 \
       --import \
       --disk bus=virtio,path=/var/lib/libvirt/images/$NAME

For IMG I used a SUSE-internal server with SLEnkins images.
The tricky part is knowing the right value for the --disk bus setting. At first I used the default but the machine wouldn't boot because it would see /dev/sda instead of /dev/vda it was expecting.

May 27, 2016

Ruby Call Graph

Call-graph makes a call graph among methods of a single Ruby file.
I made it to help me orient myself in unfamiliar legacy code and to help identify cohesive parts that could be split out.
Yes, it is quick and dirty.


One file in YaST has around 2700 lines and 73 methods. The call graph below was made with
$ ./call-graph ../yast/packager/src/modules/Packages.rb
$ dot -Tpng -oPackages.png ../yast/packager/src/modules/
If the resulting size is too big, use ImageMagick:
$ convert Packages.png -resize 1200 Packages-small.png
Packages.png, an example output
Packages.png, an example output