これによりフォーラムが壊れました。Docker コンテナは再起動しましたが、フォーラムは起動しませんでした。幸い、アップグレード前に VM スナップショットを取得していたので、それを復元しています。
ログ：
Tasks: TOP => db:migrate
(See full trace by running task with --trace)
I, [2022-04-14T15:20:51.896917 #1] INFO -- : == 20220304162250 EnableUnaccentExtension: migrating =========
-- enable_extension("unaccent")
I, [2022-04-14T15:20:51.897218 #1] INFO -- : Terminating async processes
I, [2022-04-14T15:20:51.897265 #1] INFO -- : Sending INT to HOME=/var/lib/postgresql USER=postgres exec chpst -u postgres:postgres:ssl-cert -U postgres:postgres:ssl-cert /usr/lib/postgresql/12/bin/postmaster -D /etc/postgresql/12/main pid: 1710
I, [2022-04-14T15:20:51.897396 #1] INFO -- : Sending TERM to exec chpst -u redis -U redis /usr/bin/redis-server /etc/redis/redis.conf pid: 1827
2022-04-14 15:20:51.897 UTC [1710] LOG: received fast shutdown request
1827:signal-handler (1649949651) Received SIGTERM scheduling shutdown...
2022-04-14 15:20:51.900 UTC [1710] LOG: aborting any active transactions
2022-04-14 15:20:51.902 UTC [1710] LOG: background worker "logical replication launcher" (PID 1719) exited with exit code 1
2022-04-14 15:20:51.904 UTC [1714] LOG: shutting down
1827:M 14 Apr 2022 15:20:51.913 # User requested shutdown...
1827:M 14 Apr 2022 15:20:51.914 * Saving the final RDB snapshot before exiting.
2022-04-14 15:20:51.965 UTC [1710] LOG: database system is shut down
1827:M 14 Apr 2022 15:20:53.157 * DB saved on disk
1827:M 14 Apr 2022 15:20:53.157 # Redis is now ready to exit, bye bye...
FAILED
--------------------
Pups::ExecError: cd /var/www/discourse && su discourse -c 'bundle exec rake db:migrate' failed with return #<Process::Status: pid 2118 exit 1>
Location of failure: /usr/local/lib/ruby/gems/2.7.0/gems/pups-1.1.1/lib/pups/exec_command.rb:117:in `spawn'
exec failed with the params {"cd"=>"$home", "hook"=>"db_migrate", "cmd"=>["su discourse -c 'bundle exec rake db:migrate'"]}
bootstrap failed with exit code 1
** FAILED TO BOOTSTRAP ** please scroll up and look for earlier error messages, there may be more than one.
./discourse-doctor may help diagnose the problem.
2dcd9aeca614c9e06ef748f673eb68203db6eae5c445253b416d666663879d6d
==================== END REBUILD LOG ====================
Failed to rebuild app.
そのマシンが「PG12に戻ろう」としている間に、もう一方のマシンで前進できるか試しています。クリーンインストールでPGをアップグレードしようとすると、「Creating missing functions in the discourse_functions schema…」の後に（500エラーを返し始め）停止します。そして tail -f shared/data/log/var-log/postgres/current を見ると、データコンテナが「移動」していることがわかりますが、以下のような「エラー」でいっぱいになっています。
discourse@discourse ERROR: relation "user_auth_tokens" does not exist at character 34
discourse@discourse STATEMENT: SELECT "user_auth_tokens".* FROM "user_auth_tokens" WHERE ((auth_token = 'XXXX=' OR
prev_auth_token = 'XXXX=') AND rotated_at > '2022-03-09 10:21:44.051357') LIMIT 1
discourse@discourse ERROR: relation "application_requests" does not exist at character 41
discourse@discourse STATEMENT: SELECT "application_requests"."id" FROM "application_requests" WHERE "application_requests"."date" = '2022-05-08' AND "application_requests"."req_type" = 0 LIMIT 1
