NRPE MySQL Client

nrpe_mysql.py

import logging

import ops.charm
import ops.framework

class MySQLNRPEClient(os.framework.Object):

  _stored = ops.framework.StoredState()
  
  def __init__(self, charm, relation_name: str):
      self._charm = charm
      self._relation_name = relation_name
      self.framework.observe(charm.on[relation_name].relation_changed, self._on_relation_update)
      self.framework.observe(charm.on[relation_name].relation_joined, self._on_relation_update)
      ### Existing charm doesn't support this, why?
      ### self.framework.observe(charm.on[relation_name].relation_departed, self._on_relation_removed)
      self._stored.set_default(
          nagios_password=None,
      )
      
  def _on_relation_update(self, event):
      app_or_unit = event.unit if event.unit else event.app
      remote_data = event.relation.data[app_or_unit]
      nagios_hostname = remote_data.get('nagios_hostname')
      if nagios_hostname is None:
         logging.debug('no "nagios_hostname" in relation data, deferring configuration')
         return
      self._ensure_nagios_password()
      self._ensure_nagios_access_to_mysql()
      
  def _ensure_nagios_password(self):
      if self._stored.nagios_password is not None:
          return
      self._stored.nagios_password = str(uuid.uuid4())
      
  def _ensure_nagios_access_to_mysql(self):
      cursor = self._charm.get_cursor_to_mysql()  ### Magic
      try:
          self._ensure_nagios_user(cursor)
          self._ensure_nagios_permissions(cursor)
      finally:
          cursor.close()
            
  def _ensure_nagios_user(self, cursor):
      if cursor.execute("SELECT ... WHERE User='nagios'"):
        logging.debug('nagios user already exists')
        return
      cursor.execute("CREATE USER 'nagios'@'localhost' IDENTIFIED BY %s", (password,))
      
  def _ensure_nagios_permissions(self, cursor):
      try:
        c.execute("SHOW GRANTS FOR 'nagios'@'localhost'")
        grants = [i[0] for i in c.fetchall()]
      except MySQLdb.OperationalError:
        grants = []
      ...
      
  def _ensure_nrpe_checks(self):
      for relation in self.model.relations[self._relation_name]:
          mydata = relation.data[self.unit]
          ...