docs/services/buildbot: update for nomad

docs/src/services/buildbot.md

@@ -2,13 +2,13 @@
 
 BuildBot is our legacy build scheduler.
 
-The buildbot master runs at
+The buildbot controller runs at
 [build.voidlinux.org](https://build.voidlinux.org) and provides
 unified scheduling to all other build tasks in the fleet.  BuildBot
 also exposes a web interface.
 
 The current status of the build infrastructure can be found on the
-build waterfall.  This view shows what each of the buildslaves is
+build waterfall.  This view shows what each of the builders is
 doing right now, and uses traffic light colors for build state.  A
 purple builder is usually a reason to contact void-ops and figure out
 what's wrong with the build host.
@@ -18,7 +18,7 @@ failed without needing to push a new commit.  Not all committers have
 access to restart failed builds this way.  If you believe that you
 should have this access, contact maldridge@.
 
-## Moving a buildslave
+## Moving a builder
 
 Don't.
 
@@ -28,8 +28,23 @@ to be moved is on the musl cluster, all musl builders will need to be
 moved with it.  Similarly, the aarch64 builders must always move as a
 pair.
 
+## Updating buildbot
+
+The buildbot controller and builders should be kept at the same buildbot
+version.
+
+1. Update the buildbot version in both the `buildbot` and
+   `buildbot-builder` Dockerfiles.
+2. Rebuild the service containers by triggering a build for the
+   `infra-buildbot` and `infra-buildbot-builder` containers in CI.
+3. Update the nomad jobs to use the new containers and restart them
+   with the task meta variable `db-upgrade = "true"`. This will run
+   any necessary migrations on startup.
+4. Re-set `db-upgrade = "false"`. The job does not need to be
+   redeployed, but on the next deployment, it will not run the upgrade.
+
 ## EOL
 
-BuildBot is slated for replacement this fall/winter.  The system will
-be replaced by the Distributed XBPS Package Builder (dxpb) which will
-resolve many of the long standing problems in the buildbot.
+BuildBot is slated for replacement in the future.  The system will
+be replaced by the Distributed XBPS Package Builder (dxpb) or nbuild
+which will resolve many of the long standing problems in the buildbot.