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+# yumrepofs
+
+Yumrepofs is a virtual Yum repo server. Packages or metadata do not co-exist on disk, but is rather stored in blob storage (ex. S3)
+
+The goal is to be able to store RPMs and serve repositories without the need for NFS.
+
+## Serving
+
+The lifecycle of a dnf call is as follows:
+
+* dnf sends a request to {baseurl}/repodata/repomd.xml
+* Server responds with metadata on where to find further metadata (ex. primary, filelists and other)
+* dnf queries metadata listed in repomd.xml
+
+The most important file in this case is definitely primary.xml. This is where dnf finds information about packages, and specifically where to fetch them from.
+
+Yumrepofs populates `href` fields with a path like this `Packages/{TASK_ID}/{KEY_ID}/{RPM_NAME}`. This in turn signes a S3 url and redirects the end user.
+
+## Updating the repo
+
+Let's start from the build step. Post-build, Peridot runs `createrepo_c` on all individual RPMs to create necessary metadata and stores that.
+
+When an update request is sent to `yumrepofsupdater` containing a specific build, `GetBuildArtifacts` is called to fetch RPMs+Metadata.
+
+Using this method, packages wouldn't need to coexist on disk to create a new repo, because that metadata could then be swapped into the correct place
+
+Yumrepofsupdater first fetches the latest yumrepofs revision of that repo+arch, unmarshals it, then swaps in-place the metadata from the `GetBuildArtifacts` call.
+
+Currently in-repo artifacts that are no longer to be found (based on NVRA), will be removed, just like with `createrepo_c`.
+
+## Comps/groups
+
+Using Peridot Catalogs, comps/groups can be declared that is later applied to every revision of target repo.
+
+[comps2peridot](https://github.com/rocky-linux/peridot-releng/tree/main/comps2peridot) can be used to generate comps in a format Peridot accepts.
+
+A configuration example can be found at [peridot-rocky](https://git.rockylinux.org/rocky/peridot-rocky/-/tree/r9)
+
+## Sqlite/Hashed hrefs
+
+Yumrepofs has something called "hashed variants" that can be created on demand. This changes package hrefs to the format of `Packages/{INITIAL}/{RPM_NAME}` (ex. `Packages/b/bash-5.1.8-4.el9.x86_64.rpm`).
+
+This variant also runs `sqliterepo_c` on metadata and stores the sqlite files in S3. This is also served the same way as any yumrepofs artifact.