laminar-config

Readme


# Warbo's Laminar Configuration #

Laminar is a simple continuous integration server. Laminar jobs are just scripts
which live in a particular directory, which this repository provides.

We don't point Laminar directly at this git repository, since the scripts might
need a variety of dependencies, etc. which might even conflict (e.g. if jobs
need different versions of GHC). Instead we define the jobs directory as a Nix
package, which lets us manage each script's dependencies independently.

## Contents ##

The `default.nix` file defines the job directory package. Build it using e.g.
`nix-build`.

The `install` script builds the job directory and points Laminar at the result.

## Garbage Collection ##

We can free up space by performing garbage collection on the Nix store, which
deletes paths that aren't 'live' (in use) anymore. Usually, paths are live if
they are installed on the system (or are a dependency of some installed
package). We don't use Nix to install our Laminar configuration, since doing so
would treat a config update like an OS update, which drags in too many other
concerns for our purposes. Hence we can't rely on this to keep our config
directory live.

Instead, the `nix-build` command automatically creates a symlink called `result`
in the current directory. This is a 'garbage collector root', whose presence
tells Nix that the Laminar directory is live. If this symlink is deleted or
renamed, the config directory will no longer be seen as live, and may be deleted
when running the garbage collector. Building a new config directory will
overwrite the `result` symlink, which makes the old directory not live anymore.

Note that installing a new Laminar config is not an atomic operation, it
consists of two atomic steps: building the new config, which also overwrites the
`result` symlink; then moving the new config into place. In between these steps
Laminar will be running a config that is no longer live, hence running the
garbage collector may delete it. This should hopefully not cause any problems.

Repository

Clone this repository using: 
  git clone http://chriswarbo.net/git/laminar-config.git

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