stack/erp5: Add failover script

Add a script in bin directory that can be called manually to turn a
replica into a primary. Being able to turn a replica into a primary
is an absolutely necessary feature of replication. It's a necessary
step of a takoever procedure.

Questions remain for automatisation. One option is to provide a url
the user may simply interact with (clickable button ...) to trigger
the script, that may also be used automatically as part of a larger
takoever procedure.

Triggering the change to primary by editing the instance parameters
- such as by removing the replication-related parameters - does not
seem best: one immediate drawback is the uncertain propagation time
of instance parameters; another is the reliance on the availability
of the SlapOS master to trigger a usually time-sensitive operation.

stack/erp5/buildout.hash.cfg

@@ -26,7 +26,7 @@ md5sum = d10b8e35b02b5391cf46bf0c7dbb1196
 
 [template-mariadb]
 filename = instance-mariadb.cfg.in
-md5sum = 78dd18b8342eea855c2c84b6a453c8c9
+md5sum = 1994cc11cc0da9c1df68ea0221e127b8
 
 [template-kumofs]
 filename = instance-kumofs.cfg.in

stack/erp5/instance-mariadb.cfg.in

@@ -383,6 +383,26 @@ eggs =
 file = ${mariadb-replication-sense:output}
 output = ${directory:plugins}/mariadb_replication.py
 
+[{{ section('mariadb-replica-become-primary') }}]
+# See https://mariadb.com/kb/en/changing-a-replica-to-become-the-primary
+recipe = slapos.cookbook:wrapper
+wrapper-path = ${directory:bin}/${:_buildout_section_name_}
+logfile = ${directory:log}/${:_buildout_section_name_}.log
+command-line =
+  set -eu
+  mysql="${binary-wrap-mysql:wrapper-path}"
+  {
+    date
+    $mysql -e "
+      STOP ALL SLAVES;
+      RESET SLAVE ALL;
+      SHOW MASTER STATUS;
+      SELECT @@global.gtid_binlog_pos;
+    "
+    echo
+  } >> "${:logfile}"
+  echo "See ${:logfile}"
+
 [{{ section('mariadb-backup-static-server-promise') }}]
 <= monitor-promise-base
 promise = check_socket_listening