Merge ~cjwatson/launchpad-layers:rabbitmq-optional-relation into launchpad-layers:main

[Colin Watson]

Allow non-relation-driven RabbitMQ configuration

This makes it easier to migrate a non-charmed Launchpad environment to a charmed deployment: everything in a given environment should use the same RabbitMQ server, so we probably want to start by using the existing one rather than demanding that the broker URLs be provided using a Juju relation.

[Guruprasad (lgp171188)]

LGTM 👍🏼

review: Approve

diff --git a/launchpad-base/config.yaml b/launchpad-base/config.yaml
index 4f2b83b..868c93b 100644
--- a/launchpad-base/config.yaml
+++ b/launchpad-base/config.yaml
@@ -206,6 +206,11 @@ options:
     type: string
     description: External base URL for private PPAs.
     default: http://private-ppa.launchpad.test/
+  rabbitmq_broker_urls:
+    type: string
+    description: >
+      Space-separated list of RabbitMQ broker URLs.  If unset, rely on the
+      rabbitmq relation instead.
   rabbitmq_user:
     type: string
     description: Username to use with RabbitMQ.
diff --git a/launchpad-base/reactive/launchpad-base.py b/launchpad-base/reactive/launchpad-base.py
index 0015a78..a6c6fa9 100644
--- a/launchpad-base/reactive/launchpad-base.py
+++ b/launchpad-base/reactive/launchpad-base.py
@@ -18,6 +18,8 @@ from charms.reactive import (
     remove_state,
     set_state,
     when,
+    when_any,
+    when_none,
     when_not,
 )
 from ols import base, postgres
@@ -43,19 +45,33 @@ def prepare_rabbitmq():
 
 
 def get_rabbitmq_uris(rabbitmq):
-    for conversation in rabbitmq.conversations():
-        for relation_id in conversation.relation_ids:
-            for unit in hookenv.related_units(relation_id):
-                hostname = hookenv.relation_get(
-                    "private-address", unit, relation_id
-                )
-                vhost = rabbitmq.vhost()
-                username = rabbitmq.username()
-                password = rabbitmq.password()
-                yield f"amqp://{username}:{password}@{hostname}/{vhost}"
-
-
-@when("ols.configured", "db.master.available", "rabbitmq.available")
+    config = hookenv.config()
+    if config["rabbitmq_broker_urls"]:
+        yield from config["rabbitmq_broker_urls"].split()
+    else:
+        for conversation in rabbitmq.conversations():
+            for relation_id in conversation.relation_ids:
+                for unit in hookenv.related_units(relation_id):
+                    hostname = hookenv.relation_get(
+                        "private-address", unit, relation_id
+                    )
+                    vhost = rabbitmq.vhost()
+                    username = rabbitmq.username()
+                    password = rabbitmq.password()
+                    yield f"amqp://{username}:{password}@{hostname}/{vhost}"
+
+
+@when_any("rabbitmq.available", "config.set.rabbitmq_broker_urls")
+def rabbitmq_available():
+    set_state("launchpad.rabbitmq.available")
+
+
+@when_none("rabbitmq.available", "config.set.rabbitmq_broker_urls")
+def rabbitmq_unavailable():
+    remove_state("launchpad.rabbitmq.available")
+
+
+@when("ols.configured", "db.master.available", "launchpad.rabbitmq.available")
 @when_not("launchpad.base.configured")
 def configure():
     db = endpoint_from_flag("db.master.available")
@@ -114,6 +130,6 @@ def config_changed():
 
 
 @hook("{requires:rabbitmq}-relation-changed")
-def rabbitmq_relation_changed():
+def rabbitmq_relation_changed(*args):
     remove_state("launchpad.base.configured")
     remove_state("service.configured")