Add README.md

README.md

@@ -0,0 +1,23 @@
+Docker registry cleanup
+-----------------------
+
+For every repository:
+
+1. Images created less than 1 day ago are kept
+
+2. Images with no defined build date (cache?) are kept
+
+3. Images with `org.opencontainers.image.version` label matching existing
+tags/branches or open pull requests are kept
+
+4. Everything else is deleted
+
+## REST API pagination race condition
+
+It seems that GitHub API pagination can "skip" a branch/tag/pull request
+if it's deleted concurrently.
+
+However, we mostly care about tags. Images for branches and pull requests
+are not as precious and can be rebuilt if necessary.
+
+Tags should never be deleted - so this isn't a real issue.