Module: Mysql_Checks

Defined in:
lib/apprentice/checks/mysql.rb

Overview

Contains MariaDB/MySQL specific methods for checking on slave health

Instance Method Summary collapse

Instance Method Details

#check_seconds_behind ⇒ Object

Get the value of 'Seconds_Behind_Master', which indicates the amount of time in seconds the slave is behind the master’s instruction set received via the replication thread. This should always be as close to zero as possible (or even zero). If this value is beyond @threshold constantly you will need to think about changing your setup to accommodate the traffic coming in from the master.

Attributes

  • @status - Uses the 'Seconds_Behind_Master' key inside the hash

  • @threshold - The globally defined threshold after which the slave is considered to be too far behind to still be an active member. The default is 120 seconds.

Return values

true or false - depending on whether or not the slave’s replication thread is behind @threshold

Examples

@status = Hash.new
@status['Slave_IO_Running'] = 'Yes'

r = check_slave_io
r.inspect # => true

@status['Slave_IO_Running'] = 'No'

r = check_slave_io
r.inspect # => false



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# File 'lib/apprentice/checks/mysql.rb', line 91

def check_seconds_behind
  return true if Integer(@status['Seconds_Behind_Master']) < @threshold
end

#check_slave_io ⇒ Object

Get the value of 'Slave_IO_Running', which, obviously, should be Yes since otherwise it would mean the slave is not replicated properly and/or has stopped because of an error.

Attributes

  • @status - Uses the 'Slave_IO_Running' key inside the hash.

Return values

true or false - depending on whether or not the slave’s replication thread is running.

Examples

@status = Hash.new
@status['Slave_IO_Running'] = 'Yes'

r = check_slave_io
r.inspect # => true

@status['Slave_IO_Running'] = 'No'

r = check_slave_io
r.inspect # => false



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# File 'lib/apprentice/checks/mysql.rb', line 59

def check_slave_io
  return true if @status['Slave_IO_Running'] == 'Yes'
  false
end

#get_mysql_status ⇒ Object

Gets the actual status from the MariaDB/MySQL slave using the Mysql2 gem. Notice that we’re using the EventMachine-enabled Mysql2::Client.

Right now it only returns the relevant error output and continues working afterwards.

Nothing is mentioned about explicitly closing a client connection in the Mysql2 docs, however, we need to be careful with the amount of connections we’re using since we might find ourselves in an environment where the number of connections is constraint for a very few.

Return values

  • @status - Contains a hash of all the relevant replication related variables to be examined by #run_checks



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# File 'lib/apprentice/checks/mysql.rb', line 16

def get_mysql_status
  begin
    client = Mysql2::Client.new(
        host: @server,
        port: @sql_port,
        username: @user,
        password: @password
    )
    result = client.query 'SHOW SLAVE STATUS;'
    if result.count > 0
      result.each do |key, state|
        @status[key] = state
      end
    end
    client.close
  rescue Exception => message
    puts message
  end
end

#run_checks ⇒ Object

Returns the relevant status HTTP code accompanied by a useful user feedback text

Attributes

  • @status - Should contain a hash with the relevant information to determine the the cluster member status. Also see #get_mysql_status.

Return values

  • response - A hash containing a HTTP :code and a :text to return to the user

Example

@status = {'Seconds_Behind_Master' => 140 }
response = self.run_checks
response.inspect # => {:code => 503, :text => 'Some text'}



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# File 'lib/apprentice/checks/mysql.rb', line 111

def run_checks
  get_mysql_status
  unless @status.empty?
    response = {code: 200, text: []}
    if !check_slave_io
      response[:text] << 'Slave IO is not running.'
    end
    if !check_seconds_behind
      response[:text] << "Slave is #{@status['Seconds_Behind_Master']} seconds behind. Threshold is #{@threshold}"
    end
    response[:code] = 503 unless response[:text].empty?
    return response
  else
    return {code: 503, text: ['Unable to determine slave status']}
  end
end