cachet-url-monitor/cachet_url_monitor/configuration.py

#!/usr/bin/env python
import abc
import logging
import re
import requests
import timeit
from yaml import load


class Configuration(object):
    """Represents a configuration file, but it also includes the functionality
    of assessing the API and pushing the results to cachet.
    """
    def __init__(self, config_file):
        #TODO(mtakaki|2016-04-26): Needs validation if the config is correct.
        #TODO(mtakaki|2016-04-28): Accept overriding settings using environment
        # variables so we have a more docker-friendly approach.
        self.config_file = config_file
        self.data = load(file(self.config_file, 'r'))
        self.expectations = [Expectaction.create(expectation) for expectation
                in self.data['endpoint']['expectation']]

    def evaluate(self):
        """Sends the request to the URL set in the configuration and executes
        each one of the expectations, one by one. The status will be updated
        according to the expectation results.
        """
        try:
            self.request = requests.request(self.data['endpoint']['method'],
                    self.data['endpoint']['url'],
                    timeout=self.data['endpoint']['timeout'])
        except requests.ConnectionError:
            logging.warning('The URL is unreachable: %s %s' %
                    (self.data['endpoint']['method'],
                        self.data['endpoint']['url']))
            self.status = 3
            return
        except requests.HTTPError:
            logging.exception('Unexpected HTTP response')
            self.status = 3
            return
        except requests.Timeout:
            logging.warning('Request timed out')
            self.status = 3
            return

        # We initially assume the API is healthy.
        self.status = 1
        for expectation in self.expectations:
            status = expectation.get_status(self.request)

            # The greater the status is, the worse the state of the API is.
            if status > self.status:
                self.status = status

    def push_status_and_metrics(self):
        params = {'id': self.data['cachet']['component_id'], 'status':
                self.status}
        headers = {'X-Cachet-Token': self.data['cachet']['token']}
        component_request = requests.put('%s/components/%d' %
                (self.data['cachet']['api_url'],
                self.data['cachet']['component_id']),
                params=params, headers=headers)
        if component_request.status_code == 200:
            # Successful update
            logging.info('Component update: status [%d]' % (self.status,))
        else:
            # Failed to update the API status
            logging.warning('Component update failed with status [%d]: API'
                    ' status: [%d]' % (component_request.status_code, self.status))

class Expectaction(object):
    """Base class for URL result expectations. Any new excpectation should extend
    this class and the name added to create() method.
    """
    @staticmethod
    def create(configuration):
        """Creates a list of expectations based on the configuration types
        list.
        """
        expectations = {
                'HTTP_STATUS': HttpStatus,
                'LATENCY': Latency,
                'REGEX': Regex
                }
        return expectations.get(configuration['type'])(configuration)

    @abc.abstractmethod
    def get_status(self, response):
        """Returns the status of the API, following cachet's component status
        documentation: https://docs.cachethq.io/docs/component-statuses
        """

    @abc.abstractmethod
    def get_message(self, response):
        """Gets the error message."""


class HttpStatus(Expectaction):
    def __init__(self, configuration):
        self.status = configuration['status']

    def get_status(self, response):
        if response.status_code == self.status:
            return 1
        else:
            return 3

    def get_message(self, response):
        return 'Unexpected HTTP status (%s)' % (response.status_code,)


class Latency(Expectaction):
    def __init__(self, configuration):
        self.threshold = configuration['threshold']

    def get_status(self, response):
        if response.elapsed.total_seconds() <= self.threshold:
            return 1
        else:
            return 2

    def get_message(self, response):
        return 'Latency above threshold: %.4f' % (response.elapsed.total_seconds(),)


class Regex(Expectaction):
    def __init__(self, configuration):
        self.regex = re.compile(configuration['regex'])

    def get_status(self, response):
        if self.regex.match(response.text):
            return 1
        else:
            return 3

    def get_message(self, response):
        return 'Regex did not match anything in the body'