feat: add single tailnet support to pgcoord (#9351)

coderd/database/migrations/000156_pg_coordinator_single_tailnet.down.sql

@@ -0,0 +1,39 @@
+BEGIN;
+
+ALTER TABLE
+	tailnet_clients
+ADD COLUMN
+	agent_id uuid;
+
+UPDATE
+	tailnet_clients
+SET
+	-- there's no reason for us to try and preserve data since coordinators will
+	-- have to restart anyways, which will create all of the client mappings.
+	agent_id = '00000000-0000-0000-0000-000000000000'::uuid;
+
+ALTER TABLE
+	tailnet_clients
+ALTER COLUMN
+	agent_id SET NOT NULL;
+
+DROP TABLE tailnet_client_subscriptions;
+DROP FUNCTION tailnet_notify_client_subscription_change;
+
+-- update the tailnet_clients trigger to the old version.
+CREATE OR REPLACE FUNCTION tailnet_notify_client_change() RETURNS trigger
+	LANGUAGE plpgsql
+	AS $$
+BEGIN
+	IF (OLD IS NOT NULL) THEN
+		PERFORM pg_notify('tailnet_client_update', OLD.id || ',' || OLD.agent_id);
+		RETURN NULL;
+	END IF;
+	IF (NEW IS NOT NULL) THEN
+		PERFORM pg_notify('tailnet_client_update', NEW.id || ',' || NEW.agent_id);
+		RETURN NULL;
+	END IF;
+END;
+$$;
+
+COMMIT;

coderd/database/migrations/000156_pg_coordinator_single_tailnet.up.sql

@@ -0,0 +1,88 @@
+BEGIN;
+
+CREATE TABLE tailnet_client_subscriptions (
+	client_id uuid NOT NULL,
+	coordinator_id uuid NOT NULL,
+	-- this isn't a foreign key since it's more of a list of agents the client
+	-- *wants* to connect to, and they don't necessarily have to currently
+	-- exist in the db.
+	agent_id uuid NOT NULL,
+	updated_at timestamp with time zone NOT NULL,
+	PRIMARY KEY (client_id, coordinator_id, agent_id),
+	FOREIGN KEY (coordinator_id)  REFERENCES tailnet_coordinators (id) ON DELETE CASCADE
+	-- we don't keep a foreign key to the tailnet_clients table since there's
+	-- not a great way to guarantee that a subscription is always added after
+	-- the client is inserted. clients are only created after the client sends
+	-- its first node update, which can take an undetermined amount of time.
+);
+
+CREATE FUNCTION tailnet_notify_client_subscription_change() RETURNS trigger
+	LANGUAGE plpgsql
+	AS $$
+BEGIN
+	IF (NEW IS NOT NULL) THEN
+		PERFORM pg_notify('tailnet_client_update', NEW.client_id || ',' || NEW.agent_id);
+		RETURN NULL;
+	ELSIF (OLD IS NOT NULL) THEN
+		PERFORM pg_notify('tailnet_client_update', OLD.client_id || ',' || OLD.agent_id);
+		RETURN NULL;
+	END IF;
+END;
+$$;
+
+CREATE TRIGGER tailnet_notify_client_subscription_change
+	AFTER INSERT OR UPDATE OR DELETE ON tailnet_client_subscriptions
+	FOR EACH ROW
+EXECUTE PROCEDURE tailnet_notify_client_subscription_change();
+
+CREATE OR REPLACE FUNCTION tailnet_notify_client_change() RETURNS trigger
+	LANGUAGE plpgsql
+	AS $$
+DECLARE
+	var_client_id uuid;
+	var_coordinator_id uuid;
+	var_agent_ids uuid[];
+	var_agent_id uuid;
+BEGIN
+	IF (NEW.id IS NOT NULL) THEN
+		var_client_id = NEW.id;
+		var_coordinator_id = NEW.coordinator_id;
+	ELSIF (OLD.id IS NOT NULL) THEN
+		var_client_id = OLD.id;
+		var_coordinator_id = OLD.coordinator_id;
+	END IF;
+
+	-- Read all agents the client is subscribed to, so we can notify them.
+	SELECT
+		array_agg(agent_id)
+	INTO
+		var_agent_ids
+	FROM
+		tailnet_client_subscriptions subs
+	WHERE
+		subs.client_id = NEW.id AND
+		subs.coordinator_id = NEW.coordinator_id;
+
+	-- No agents to notify
+	if (var_agent_ids IS NULL) THEN
+		return NULL;
+	END IF;
+
+	-- pg_notify is limited to 8k bytes, which is approximately 221 UUIDs.
+	-- Instead of sending all agent ids in a single update, send one for each
+	-- agent id to prevent overflow.
+	FOREACH var_agent_id IN ARRAY var_agent_ids
+	LOOP
+		PERFORM pg_notify('tailnet_client_update', var_client_id || ',' || var_agent_id);
+	END LOOP;
+
+	return NULL;
+END;
+$$;
+
+ALTER TABLE
+	tailnet_clients
+DROP COLUMN
+	agent_id;
+
+COMMIT;

coderd/database/migrations/testdata/fixtures/000130_ha_coordinator.up.sql

@@ -18,7 +18,7 @@ VALUES
 	);
 
 INSERT INTO tailnet_agents
-(id, coordinator_id, updated_at, node)
+	(id, coordinator_id, updated_at, node)
 VALUES
 	(
 		'c0eebc99-9c0b-4ef8-bb6d-6bb9bd380a11',

coderd/database/migrations/testdata/fixtures/000156_pg_coordinator_single_tailnet.up.sql

@@ -0,0 +1,9 @@
+INSERT INTO tailnet_client_subscriptions
+	(client_id, agent_id, coordinator_id, updated_at)
+VALUES
+	(
+		'b0eebc99-9c0b-4ef8-bb6d-6bb9bd380a11',
+		'c0eebc99-9c0b-4ef8-bb6d-6bb9bd380a11',
+		'a0eebc99-9c0b-4ef8-bb6d-6bb9bd380a11',
+		'2023-06-15 10:23:54+00'
+	);