Add max_connect_errors configuration option.

This change adds the config option max_connect_errors for MySQL to this
charm and sets a default of 100.
Commit also includes the inclusion of this (default) config setting in the
unit tests.
Closes-Bug: #1776908

Change-Id: I33b9e29bd64ad8a1fec0edc3dfd657a87648b537

config.yaml

@@ -365,3 +365,13 @@ options:
       This configuration option represents the warning and critical percentages
       that are used to check the number of threads connected to MySQL.
       The value should be written as a string containing two numbers separated by commas.
+  max-connect-errors:
+    type: int
+    default: 100
+    description: |
+      This setting limits the number of successive unsuccessful connection
+      requests that a host can make to MySQL. After max-connect-errors
+      successive connection requests from a host are interrupted without a
+      successful connection, the MySQL server blocks that host from making
+      further connections.
+      This setting is only for Ubuntu Xenial and newer releases.

hooks/percona_hooks.py

@@ -273,6 +273,7 @@ def render_config(hosts=None):
         'binlogs_max_size': config('binlogs-max-size'),
         'binlogs_expire_days': config('binlogs-expire-days'),
         'performance_schema': config('performance-schema'),
+        'max_connect_errors': config('max-connect-errors'),
         'is_leader': is_leader(),
         'server_id': get_server_id(),
         'series_upgrade': is_unit_upgrading_set(),

templates/mysqld.cnf

@@ -44,6 +44,10 @@ myisam-recover         = {{ myisam_recover }}
 max_connections = {{ max_connections }}
 {% endif %}
 
+{% if max_connect_errors %}
+max_connect_errors = {{ max_connect_errors }}
+{% endif %}
+
 {% if wait_timeout != -1 -%}
 # Seconds before clearing idle connections
 wait_timeout = {{ wait_timeout }}

unit_tests/test_percona_hooks.py

@@ -929,6 +929,7 @@ class TestConfigs(CharmTestCase):
             'binlogs_path': self.default_config['binlogs-path'],
             'cluster_name': 'juju_cluster',
             'binlogs_expire_days': self.default_config['binlogs-expire-days'],
+            'max_connect_errors': self.default_config['max-connect-errors'],
             'ipv6': False,
             'innodb_file_per_table':
             self.default_config['innodb-file-per-table'],
@@ -987,6 +988,7 @@ class TestConfigs(CharmTestCase):
             'binlogs_path': self.default_config['binlogs-path'],
             'binlogs_expire_days': self.default_config['binlogs-expire-days'],
             'performance_schema': self.default_config['performance-schema'],
+            'max_connect_errors': self.default_config['max-connect-errors'],
             'key_buffer': '32M',
             'default_storage_engine': 'InnoDB',
             'wsrep_log_conflicts': True,
@@ -1052,6 +1054,7 @@ class TestConfigs(CharmTestCase):
             'binlogs_path': self.default_config['binlogs-path'],
             'binlogs_expire_days': self.default_config['binlogs-expire-days'],
             'performance_schema': self.default_config['performance-schema'],
+            'max_connect_errors': self.default_config['max-connect-errors'],
             'key_buffer': '32M',
             'default_storage_engine': 'InnoDB',
             'wsrep_log_conflicts': True,
@@ -1130,6 +1133,7 @@ class TestConfigs(CharmTestCase):
             'binlogs_path': self.default_config['binlogs-path'],
             'binlogs_expire_days': self.default_config['binlogs-expire-days'],
             'performance_schema': self.default_config['performance-schema'],
+            'max_connect_errors': self.default_config['max-connect-errors'],
             'key_buffer': '32M',
             'default_storage_engine': 'InnoDB',
             'wsrep_log_conflicts': True,
@@ -1145,6 +1149,68 @@ class TestConfigs(CharmTestCase):
             context,
             perms=0o444)
 
+    @mock.patch.object(hooks, 'is_unit_upgrading_set')
+    @mock.patch.object(os, 'makedirs')
+    @mock.patch.object(hooks, 'get_cluster_host_ip')
+    @mock.patch.object(hooks, 'get_wsrep_provider_options')
+    @mock.patch.object(PerconaClusterHelper, 'parse_config')
+    @mock.patch.object(hooks, 'render')
+    @mock.patch.object(hooks, 'sst_password')
+    @mock.patch.object(hooks, 'lsb_release')
+    def test_render_config_max_connect_errors(
+            self,
+            lsb_release,
+            sst_password,
+            render,
+            parse_config,
+            get_wsrep_provider_options,
+            get_cluster_host_ip,
+            makedirs,
+            mock_is_unit_upgrading_set):
+        mock_is_unit_upgrading_set.return_value = False
+        parse_config.return_value = {'key_buffer': '32M'}
+        get_cluster_host_ip.return_value = '10.1.1.1'
+        get_wsrep_provider_options.return_value = None
+        sst_password.return_value = 'sstpassword'
+        lsb_release.return_value = {'DISTRIB_CODENAME': 'bionic'}
+        self.test_config.set('max-connect-errors', 42)
+
+        context = {
+            'wsrep_slave_threads': 48,
+            'server_id': hooks.get_server_id(),
+            'server-id': hooks.get_server_id(),
+            'is_leader': hooks.is_leader(),
+            'series_upgrade': hooks.is_unit_upgrading_set(),
+            'private_address': '10.1.1.1',
+            'innodb_autoinc_lock_mode': '2',
+            'cluster_hosts': '',
+            'enable_binlogs': self.default_config['enable-binlogs'],
+            'sst_password': 'sstpassword',
+            'sst_method': self.default_config['sst-method'],
+            'pxc_strict_mode': 'enforcing',
+            'binlogs_max_size': self.default_config['binlogs-max-size'],
+            'cluster_name': 'juju_cluster',
+            'innodb_file_per_table':
+            self.default_config['innodb-file-per-table'],
+            'table_open_cache': self.default_config['table-open-cache'],
+            'binlogs_path': self.default_config['binlogs-path'],
+            'binlogs_expire_days': self.default_config['binlogs-expire-days'],
+            'performance_schema': self.default_config['performance-schema'],
+            'key_buffer': '32M',
+            'default_storage_engine': 'InnoDB',
+            'wsrep_log_conflicts': True,
+            'ipv6': False,
+            'wsrep_provider': '/usr/lib/galera3/libgalera_smm.so',
+            'max_connect_errors': 42,
+        }
+
+        hooks.render_config()
+        hooks.render.assert_called_once_with(
+            'mysqld.cnf',
+            '/etc/mysql/percona-xtradb-cluster.conf.d/mysqld.cnf',
+            context,
+            perms=0o444)
+
 
 class TestRenderConfigRestartOnChanged(CharmTestCase):
     TO_PATCH = [