backend_database relation

This reference documentation details the implementation of the backend-database relation. The file implementing these relations can be found here: src/relations/backend_database.py.

Expected Interface

These are the expected contents of the databags in this relation (all values are examples, generated in a running test instance):

category	keys	pgbouncer-k8s-o…	postgresql-k8s/0
metadata	endpoint	'backend-databa…	'database'
	leader	True	True
application data	data	{"endpoints":"postgresql-k8s", "password":"18cqKCp19xOPBh", "read-only-endpoints":"postgresql-k8s","username":"relation_18", "version":"12.9"}	{"database":"postgresql", "extra-user-roles","SUPERUSER"
	database	pgbouncer
	endpoints		postgresql-k8s-…
	extra-user-roles	SUPERUSER
	password		18cqKCp19xOPBh
	read-only-endpoints		postgresql-k8s-…
	username		relation_18
	version		12.9

Hook Handler Flowcharts

These flowcharts detail the control flow of the hooks in this program. Unless otherwise stated, a hook deferral is always followed by a return.

Backend Database Created Hook

flowchart TD
  hook_fired([backend-database-requested Hook]) --> is_leader{Is current unit leader?}
  is_leader -- no --> rtn([return])
  is_leader -- yes --> is_running{Is pgbouncer running?}
  is_running -- no --> defer2>defer]
  is_running -- yes --> is_backend_ready{is backend database charm ready, and has pgbouncer been provided with the necessary relation data?}
  is_backend_ready -- no --> defer>defer]
  is_backend_ready -- yes --> generate_user[Generate username & password]
  generate_user --> create_auth_func[create auth function on postgres]
  create_auth_func --> save_auth_data[update pgbouncer config, and save auth data to container and peer databag]
  save_auth_data --> update_relations[update postgres endpoints in client relations]
  update_relations --> update_status[update charm status]
  update_status --> rtn2([return])

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Backend Database Departed Hook

flowchart TD
  hook_fired([backend-database-relation-departed Hook]) --> update_info[update relation connection information]
  update_info --> is_this_unit_departing{Is this unit the departing unit?}
  is_this_unit_departing -- yes --> tell_peers[update unit databag to tell peers this unit is departing]
  tell_peers --> rtn([return])
  is_this_unit_departing -- no --> is_leader{is this unit the leader, and is it departing}
  is_leader -- no --> rtn2([return])
  is_leader -- yes --> scale_down{Is this application scaling down, but not to 0?}
  scale_down -- yes --> rtn3([return])
  scale_down -- no --> remove_auth[Remove auth function, and   delete auth user]
  remove_auth --> rtn4([return])

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Backend Database Broken Hook

flowchart TD
  hook_fired([backend-database-relation-broken Hook]) --> check_depart{Is this unit not the leader, or is the relation_departing flag  in the unit databag?}
  check_depart -- yes --> rtn([return])
  check_depart -- no --> is_cfg{Is pgbouncer config available?}
  is_cfg -- no --> defer>defer]
  is_cfg -- yes --> remove_auth[Remove authentication information from pgbouncer config]
  remove_auth --> rtn2([return])

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