Wait for MariaDB to be accessible via HAProxy

Explicitly wait for the database to be accessible via the load balancer.
Sometimes it can reject connections even when all database services are up,
possibly due to the health check polling in HAProxy.

Closes-Bug: #1840145
Change-Id: I7601bb710097a78f6b29bc4018c71f2c6283eef2

ansible/roles/mariadb/tasks/recover_cluster.yml

@@ -190,3 +190,5 @@
   when:
     - bootstrap_host is defined
     - bootstrap_host != inventory_hostname
+
+- import_tasks: wait_for_loadbalancer.yml

ansible/roles/mariadb/tasks/register.yml

@@ -13,6 +13,8 @@
       priv: "*.*:USAGE"
   run_once: True
 
+- import_tasks: wait_for_loadbalancer.yml
+
 - name: Creating the Percona XtraBackup database
   kolla_toolbox:
     module_name: mysql_db

ansible/roles/mariadb/tasks/wait_for_loadbalancer.yml

@@ -0,0 +1,16 @@
+---
+# Explicitly wait for the database to be accessible via the load balancer.
+# Sometimes it can reject connections even when all database services are up,
+# due to the health check polling in HAProxy.
+- name: wait for MariaDB to be available via HAProxy
+  wait_for:
+    host: "{{ database_address }}"
+    port: "{{ database_port }}"
+    connect_timeout: 1
+    timeout: 60
+    search_regex: "MariaDB"
+  register: check_mariadb_port
+  until: check_mariadb_port is success
+  retries: 10
+  delay: 6
+  run_once: True