Add more about versioning

Fixes coop-cloud/abra#159

docs/packager-guide.md

@@ -4,17 +4,54 @@ title: Packager guide
 
 ## How apps are versioned
 
-We simply take the version of the packaged app to be the same as the version of
+Co-op Cloud follows the version scheme of the applications we're packaging, as
-the main `app` service in the `compose.yml` file. So, if you are deploying
+far as possible; for example, [version `1.13.4` of our Gitea recipe][gitea]
-`gitea/gitea:1.13.4` then the version of your Gitea app package version is
+contains version `1.13.4` of Gitea. We're trying not to invent a new versioning
-`1.13.4`.
+scheme.
 
-Additionally, most apps have underlying services like databases and/or caches.
+This approach is still work-in-progress.
-When a new version is published and available in the `compose.yml` we use the
-`<version>_<revision>` syntax. So, if you are still on `1.13.4` for Gitea but
-you have `mariadb:10.6` upgraded from `mariadb:10.5` then the Gitea app package
-version would be `1.13.4_1`.
 
-Our high level goals of app versioning on this project are not to invent a new
+Versions are based on [Docker image tags][tags]: we don't currently have a plan for apps
-versioning system. Therefore, we try to follow the upstream versioning as much
+which only publish a `latest` or `master` tag, for instance.
-as possible. This scheme is still a work in progress.
+
+### Versioning different services
+
+Most apps have underlying services like databases and/or caches.
+
+When there's a new version of one of these services, but not the "main" service,
+we add/increment the `_<revision>` part at the end of the version.
+
+So, if you are still on `1.13.4` for Gitea, but you have `mariadb:10.6` upgraded
+from `mariadb:10.5`, then the Gitea recipe package version would be `1.13.4_1`.
+
+If you run `abra recipe gitea versions`, you'll see that there are a few
+available versions of the `gitea` recipe, two with the same version of the
+`gitea` image:
+
+```
+1.14.1-rootless:
+ - app (gitea/gitea:1.14.1-rootless, 6244e9fc)
+ - db (mariadb:10.5, 36288c67)
+1.14.1-rootless_1:
+ - app (gitea/gitea:1.14.1-rootless, 6244e9fc)
+ - db (mariadb:10.6, 718cb856)
+1.14.2-rootless:
+ - app (gitea/gitea:1.14.2-rootless, bedf8d12)
+ - db (mariadb:10.6, 718cb856)
+```
+
+Versions `1.14.1-rootless` and `1.14.1-rooless_1`  differ only in their version
+of the `mariadb` service. If there had been several updates to the `mariadb`
+image in between updates to the `gitea` image, there might have also been
+`1.14.1-rooless_2`, `1.14.1-rooless_3` -- this is more likely with recipes which
+include services with several different images.
+
+!!! note 
+
+	Not all of these updates will be released as installable Co-op Cloud recipes
+	-- in this example, there's no version with `gitea:1.14.2-rootless` and
+	`mariadb:10.5`. If you need a specific combination, create a pull request or
+	issue in the repository for the app recipe!
+
+[gitea]: https://git.autonomic.zone/coop-cloud/gitea/src/tag/1.13.4
+[tags]: https://docs.docker.com/engine/reference/commandline/tag/