I have two Hudson jobs:
I want to make Launch-instance dependent on the other one, so that triggering Launch-instance automatically causes Upload to be run first. Can I achieve this using Hudson's built-in features or with a plugin?
Note that I do not want Upload to always trigger Launch-instance, which is what the "Build after other projects are built" option on Launch-instance would do. What I want is more analogous to how depends attribute works for an Ant target.
You can use the downstream or upstream dependencies. You should use "Build Triggers" -> Build after other projects are built and/or post-build actions in the configure part of the project.
What about building Upload by calling its build URL with wget as the first build step? Then adding the beef build steps of Launch-instance.
Or for a fancier approach, perhaps use the Remote access API.
Aha, found it! Here I'm building on miki's answer which showed the way but didn't fully solve this for me.
As it says in the Spanish-language article about launching Hudson builds which was linked to from the comments of Hudson's Remote access API page that miki linked to:
En la sección "Build Triggers" [...] marcamos la opción "Trigger builds remotely (e.g., from scripts)". Al marcar esta opción vemos como aparece el cuadro de texto "Authentication Token". Aquí pondremos el nombre del token de autenticación.
(It seems the benefits of knowing Spanish are starting to materialise... :-)
So, turns out Hudson provides a handy built-in option for triggering builds remotely. In Build Triggers section (of Upload job in my case) you can enable remote builds and set an auth token (see screenshot above). Then you can launch a build by accessing a certain URL containing that token. In my case, the first build step of Launch-instance looks like:
wget http://[hudson-url]/job/Upload/build?token=TEST
sleep 10
This works even if anonymous builds are disabled and simply trying to access the build URL would yield "403 Forbidden".