ambari/ambari-agent/src/main/python/ambari_agent/NetUtil.py

# Licensed to the Apache Software Foundation (ASF) under one or more
# contributor license agreements.  See the NOTICE file distributed with
# this work for additional information regarding copyright ownership.
# The ASF licenses this file to You under the Apache License, Version 2.0
# (the "License"); you may not use this file except in compliance with
# the License.  You may obtain a copy of the License at
#
#     http://www.apache.org/licenses/LICENSE-2.0
#
# Unless required by applicable law or agreed to in writing, software
# distributed under the License is distributed on an "AS IS" BASIS,
# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
# See the License for the specific language governing permissions and
# limitations under the License.


from urlparse import urlparse
import time
import logging
import httplib
from ssl import SSLError

logger = logging.getLogger()

class NetUtil:

  CONNECT_SERVER_RETRY_INTERVAL_SEC = 10
  HEARTBEAT_IDDLE_INTERVAL_SEC = 10
  MINIMUM_INTERVAL_BETWEEN_HEARTBEATS = 0.1

  # Url within server to request during status check. This url
  # should return HTTP code 200
  SERVER_STATUS_REQUEST = "{0}/cert/ca"

  # For testing purposes
  DEBUG_STOP_RETRIES_FLAG = False

  def checkURL(self, url):
    """Try to connect to a given url. Result is True if url returns HTTP code 200, in any other case
    (like unreachable server or wrong HTTP code) result will be False
    """
    logger.info("Connecting to " + url);
    
    try:
      parsedurl = urlparse(url)
      ca_connection = httplib.HTTPSConnection(parsedurl[1])
      ca_connection.request("HEAD", parsedurl[2])
      response = ca_connection.getresponse()  
      status = response.status    
      
      requestLogMessage = "HEAD %s -> %s"
      
      if status == 200:
        logger.debug(requestLogMessage, url, str(status) ) 
        return True
      else: 
        logger.warning(requestLogMessage, url, str(status) )
        return False
    except SSLError as slerror:
      logger.error(str(slerror))
      logger.error("SSLError: Failed to connect. Please check openssl library versions. \n" +
                   "Refer to: https://bugzilla.redhat.com/show_bug.cgi?id=1022468 for more details.")
      return False
    
    except Exception, e:
      logger.warning("Failed to connect to " + str(url) + " due to " + str(e) + "  ")
      return False

  def try_to_connect(self, server_url, max_retries, logger = None):
    """Try to connect to a given url, sleeping for CONNECT_SERVER_RETRY_INTERVAL_SEC seconds
    between retries. No more than max_retries is performed. If max_retries is -1, connection
    attempts will be repeated forever until server is not reachable
    Returns count of retries
    """
    if logger is not None:
      logger.debug("Trying to connect to %s", server_url)
      
    retries = 0
    while (max_retries == -1 or retries < max_retries) and not self.DEBUG_STOP_RETRIES_FLAG:
      server_is_up = self.checkURL(self.SERVER_STATUS_REQUEST.format(server_url))
      if server_is_up:
        break
      else:
        if logger is not None:
          logger.warn('Server at {0} is not reachable, sleeping for {1} seconds...'.format(server_url,
            self.CONNECT_SERVER_RETRY_INTERVAL_SEC))
        retries += 1
        time.sleep(self.CONNECT_SERVER_RETRY_INTERVAL_SEC)
    return retries