Add automatic garbage collection service to Trovebaserock/sam/artifact-cache-garbage-collect

We are now using Trove as an artifact server for the Mason continuous
delivery system, which can fill up the disk pretty quickly.

This adds a rudimetary system for cleaning up old artifacts from an
artifact cache server.

Note that it does not have any smarts about what to remove other than
checking the 'mtime', If you have important release artifacts in the
artifact cache, don't run `trove-gc` or enable the trove-garbage-collect
service.

It wraps the `morph gc` command, currently, so Morph is required on the
system. Morph is included in Trove systems via the 'tools' stratum right
now.

It is hardcoded to remove artifacts until there is at least 15GB of free
disk space, and to run once an hour.

No cleanup of Git or Lorry data is done.

1 files changed, 9 insertions, 0 deletions

diff --git a/units/trove-garbage-collect.timer b/units/trove-garbage-collect.timer
new file mode 100644
index 0000000..636acea
--- /dev/null
+++ b/units/trove-garbage-collect.timer
@@ -0,0 +1,9 @@
+[Unit]
+Description=Remove old artifacts once every hour
+
+[Timer]
+OnUnitActiveSec=1h
+
+[Install]
+WantedBy=multi-user.target
+Also=trove-garbage-collect.service