Servant - a Python framework for building (micro)services

Talk given at Denver Python Meetup about Servant, a Python framework for building (micro)services.

https://www.meetup.com/Denver-Python-Meetup/events/233917210/
https://github.com/brianz/servant

Transcript

1. Servant
   a Python framework for building (micro)services
   

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2. About me
   Brian Zambrano
   brianz@gmail.com
   https://github.com/brianz/
   • Originally from San Francisco Bay Area
   • Moved to Ft. Collins, CO in 2014
   • Have been writing Python since 2001
   

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3. What is Servant?
   • Servant is a Python library/framework
   for authoring and communicating with
   services
   • Servant is to services what Django,
   Rails or Flask are to web applications
   • Primary use case is internal services
   https://github.com/brianz/servant
   

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4. Why Servant?
   • REST is great, but has many limitations and problems
   • HTTP by definition
   • Requires a running server
   • Usually end up using a wrapper library
   • Various interpretations
   • Can be challenging to get your Resources right
   

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5. Using servant as a client
   import servant.client
   client = servant.client.Client(
   'calculator_service', version=1)
   response = client.add(number1=10, number2=15)
   if response.is_error():
   print response.errors, response.field_errors
   else:
   print response.result
   

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6. Authoring a service
   from servant.service.base import Service
   import actions
   class Calculator(Service):
   name = 'calculator_service'
   version = 1
   action_map = {
   'add': actions.AddAction,
   'subtract': actions.SubtractAction,
   }
   

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7. Implement an Action
   import servant.fields
   from servant.service.actions import Action
   class AddAction(Action):
   number1 = servant.fields.IntField(
   required=True,
   in_response=True,
   )
   number2 = servant.fields.IntField(
   required=True,
   in_response=True,
   )
   result = servant.fields.IntField(
   in_response=True,
   )
   def run(self, **kwargs):
   self.result = self.number1 + self.number2
   

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8. Demo
   

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9. Issues with Servant
   • Currently Python only. Other languages would need
   a Servant library implemented.
   • No mechanism for exploration...need knowledge of
   service before hitting it
   • Can't simply use curl to hit an endpoint
   • Need another layer to expose a service publicly
   (i.e., hitting from Javascript)
   

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10. Using servant as a client
    import servant.client
    client = servant.client.Client(
    'calculator_service', version=1)
    response = client.add(number1=10, number2=15)
    if response.is_error():
    print response.errors, response.field_errors
    else:
    print response.result
    

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11. Using servant as a client
    import servant.client
    client = servant.client.Client(
    'calculator_service', version=1)
    response = client.add(number1=10, number2=15)
    if response.is_error():
    print response.errors, response.field_errors
    else:
    print response.result
    

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12. Using servant as a client
    import servant.client
    client = servant.client.Client(
    'calculator_service', version=1)
    client.configure('http', host='192.168.88.100', port=8888)
    response = client.add(number1=10, number2=15)
    if response.is_error():
    print response.errors, response.field_errors
    else:
    print response.result
    

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13. Using servant as a client
    import servant.client
    client = servant.client.Client(
    'calculator_service', version=1)
    client.configure('http', host='192.168.88.100', port=8888)
    response = client.add(number1=10, number2=15)
    if response.is_error():
    print response.errors, response.field_errors
    else:
    print response.result
    

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14. Demo
    

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15. Transports and Brokers
    Currently, servant supports two
    brokers for communication:
    • local library
    • HTTP
    Pretty easy to add others
    

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16. HTTP Transport
    from .base import BaseTransport
    import requests
    class HttpTransport(BaseTransport):
    def __init__(self):
    self.__url = 'http://localhost:8000'
    def __repr__(self):
    return 'HttpTransport at %s' % (self.__url, )
    def configure(self, host='localhost', port=8000, scheme='http'):
    self.__url = '%s://%s:%s' % (scheme, host, port)
    def is_connected(self):
    return True
    def send(self, data):
    headers = {'content-type': 'application/json'}
    response = requests.post(self.__url, data=data, headers=headers)
    return response.text
    

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17. Local Transport
    class LocalTransport(BaseTransport):
    def __init__(self):
    super(LocalTransport, self).__init__()
    self.__service = None
    def __repr__(self):
    return self.__class__.__name__
    def configure(self, service_name='', service_version='', service_meta=None):
    self.service = self._import_and_instantiate_service(service_name,
    service_version)
    @property
    def service(self):
    raise AttributeError("Cannot access service property directly")
    @service.setter
    def service(self, service_instance):
    self.__service = service_instance
    def _import_and_instantiate_service(self, service_name, service_version):
    # Do a bunch of stuff to import and instantiate the service.
    def send(self, request):
    return self.__service.handle_request(request)
    

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18. Field validation
    def do_divide():
    response = client.divide(
    numerator=100, denominator='abc')
    if response.is_error():
    print response.errors, response.field_errors
    else:
    print response.quotient
    None, Bunch(denominator=[Bunch(error=u"Number 'abc' failed
    to convert to a decimal", hint=u"Number 'abc' failed to
    convert to a decimal")])
    

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19. Errors
    def do_divide():
    response = client.divide(
    numerator=100, denominator=0)
    if response.is_error():
    print response.errors, response.field_errors
    else:
    print response.quotient
    [u'Unexpected service error: x / 0'], None
    

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20. Handing Errors
    def run(self, **kwargs):
    if self.denominator == 0:
    raise ActionError('Cannot divide by zero')
    self.quotient = self.numerator / self.denominator
    

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21. Service protocol
    {u'actions': [{u'action_name': u'charge_credit_card',
    u'errors': [{u'error': u'Expired Card',
    u'error_type': u'WARNING',
    u'hint': u''}],
    u'field_errors': None,
    u'results': {u'approved_amount': 0.0,
    u'processor_response_code': 21,
    u'transaction_number': 20,
    u'transaction_status': u'Declined'}}],
    u'response': {u'correlation_id': u'c1fe850b-d449-45d7-
    b8be-9b1ff7c7108b',
    u'errors': [{u'error': u'Expired Card',
    u'error_type': u'WARNING',
    u'hint': u''}],
    u'name': u'payment_service',
    u'response_time': u'5.64651',
    u'version': 1}}
    

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