Merge ~cjwatson/launchpad-layers:set-role-after-connecting into launchpad-layers:main

[Colin Watson]

Set database role after connecting

https://code.launchpad.net/~cjwatson/launchpad/+git/launchpad/+merge/432027 allows us to connect using a single set of user credentials provided via the `pgsql` interface, and then switch to whichever database role we need for a given task. This simplifies a lot of our deployment arrangements.

[Guruprasad (lgp171188)]

LGTM 👍🏼

review: Approve

diff --git a/launchpad-base/lib/charms/launchpad/base.py b/launchpad-base/lib/charms/launchpad/base.py
index 71f0dbe..2a182fe 100644
--- a/launchpad-base/lib/charms/launchpad/base.py
+++ b/launchpad-base/lib/charms/launchpad/base.py
@@ -190,6 +190,5 @@ def update_pgpass(dsn):
 
 def strip_dsn_authentication(dsn):
     parsed_dsn = parse_dsn(dsn)
-    parsed_dsn.pop("user", None)
     parsed_dsn.pop("password", None)
     return make_dsn(**parsed_dsn)
diff --git a/launchpad-base/reactive/launchpad-base.py b/launchpad-base/reactive/launchpad-base.py
index b3bd439..0015a78 100644
--- a/launchpad-base/reactive/launchpad-base.py
+++ b/launchpad-base/reactive/launchpad-base.py
@@ -21,7 +21,6 @@ from charms.reactive import (
     when_not,
 )
 from ols import base, postgres
-from psycopg2.extensions import parse_dsn
 
 
 # Monkey-patch layer:ols.
@@ -73,10 +72,6 @@ def configure():
     config["db_standby"] = ",".join(
         strip_dsn_authentication(dsn) for dsn in db_standby
     )
-    # XXX cjwatson 2022-09-23: This is a layering violation, since it's
-    # specific to the appserver.  We need to teach Launchpad to be able to
-    # log in as one role and then switch to another.
-    config["db_user"] = parse_dsn(db_primary)["user"]
     config["rabbitmq_broker_urls"] = sorted(get_rabbitmq_uris(rabbitmq))
     configure_lazr(
         config,
diff --git a/launchpad-base/templates/launchpad-base-lazr.conf b/launchpad-base/templates/launchpad-base-lazr.conf
index 9e597f5..748aaa2 100644
--- a/launchpad-base/templates/launchpad-base-lazr.conf
+++ b/launchpad-base/templates/launchpad-base-lazr.conf
@@ -47,6 +47,7 @@ git_ssh_root: git+ssh://{{ domain_git }}/
 {{- opt("db_statement_timeout", db_statement_timeout) }}
 rw_main_primary: {{ db_primary }}
 rw_main_standby: {{ db_standby or db_primary }}
+set_role_after_connecting: True
 {{- opt("soft_request_timeout", soft_request_timeout) }}
 
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