Add documentation to migrate to 0.6

doc/book/src/SUMMARY.md

@@ -44,5 +44,6 @@
 - [Working Documents](./working_documents/index.md)
   - [S3 compatibility target](./working_documents/compatibility_target.md)
   - [Load balancing data](./working_documents/load_balancing.md)
+  - [Migrating from 0.5 to 0.6](./working_documents/migration_06.md)
   - [Migrating from 0.3 to 0.4](./working_documents/migration_04.md)
   - [Design draft](./working_documents/design_draft.md)

doc/book/src/working_documents/migration_06.md

@@ -0,0 +1,46 @@
+# Migrating from 0.5 to 0.6
+
+**This guide explains how to migrate to 0.6 if you have an existing 0.5 cluster.
+We don't recommend trying to migrate directly from 0.4 or older to 0.6.**
+
+**We make no guarantee that this migration will work perfectly:
+back up all your data before attempting it!**
+
+Garage v0.6 (not yet released) introduces a new data model for buckets,
+that allows buckets to have many names (aliases).
+Buckets can also have "private" aliases (called local aliases),
+which are only visible when using a certain access key.
+
+This new data model means that the metadata tables have changed quite a bit in structure,
+and a manual migration step is required.
+
+The migration steps are as follows:
+
+1. Disable api and web access for some time (Garage does not support disabling
+   these endpoints but you can change the port number or stop your reverse
+   proxy for instance).
+
+2. Do `garage repair -a --yes tables` and `garage repair -a --yes blocks`,
+   check the logs and check that all data seems to be synced correctly between
+   nodes.
+
+4. Turn off Garage 0.5
+
+5. **Backup your metadata folders!!**
+
+6. Turn on Garage 0.6
+
+7. At this point, `garage bucket list` should indicate that no buckets are present
+   in the cluster. `garage key list` should show all of the previously existing
+   access key, however these keys should not have any permissions to access buckets.
+
+8. Run `garage migrate buckets050`: this will populate the new bucket table with
+   the buckets that existed previously. This will also give access to API keys
+   as it was before.
+
+9. Check that all your buckets indeed appear in `garage bucket list`, and that
+   keys have the proper access flags set. If that is not the case, revert
+   everything and file a bug!
+
+10. Your upgraded cluster should be in a working state. Re-enable API and Web
+    access and check that everything went well.