Hammock, a Good Place to Rest

® Copyright Stratoscale www.stratoscale.com @stratoscale +1 877 420 3244
Hammock
A Good Place to REST
June, 2016
Eyal Posener eyal@stratoscale.com
Software Engineer / Stratoscale

Agenda
❏ Nice to meet you - I’m Eyal
❏ Software developer at Stratoscale (~2 years)
❏ Why am I presenting Hammock?
❏ Stratoscale has moved to microservices in containers:
❏ Currently 8 internally developed REST services.
❏ Internal & external communication.
❏ Coverage:
1. Creating a simple REST application with Python.
2. What was missing for Stratoscale.
3. Hammock

Introducing WSGI - (Web Server Gateway Interface)Web Server
Gateway Interfa
PEP 3333 / PEP 333 Web Server Gateway Interface.
❏ Defines a simple API between the server/gateway and
framework(/application).
Server/
Gateway
Framework
WSGI

Many Many WSGI Players

Application
An application is developed with a specific framework.
Server/
Gateway
Framework
WSGI
Application
Framework
API

Let’s build a REST Server in Falcon
❏ REpresentational State Transfer
❏ A convention for communication:
Path pattern
HTTP
method
Action
Status
(usually)
Response
(usually)
Request Args
Location
.../<item>s POST Create new item 201/202 Dict Body
.../<item>s GET List all Items 200 List of dicts Query
.../<item>s/<item>_id GET Get <item> 200 Dict Query
.../<item>s/<item>_id PATCH/PUT Update <item> 202 Dict Body
.../<item>s/<item>_id DELETE Delete <item> 204 Nothing Query

class Files(object):
def on_post(self, req, resp): # create
pass
def on_get(self, req, resp): # list
pass
class File(object):
def on_get(self, req, resp, file_id): # get one
pass
def on_delete(self, req, resp, file_id): # delete
pass
def on_patch(self, req, resp, file_id): # update
pass
app = falcon.API()
app.add_route('/files', Files())
app.add_route('/files/{file_id}', File())
Falcon Application Example

import files # Business logic is here
def on_get(self, req, resp):
"""List files"""
# First, extract request arguments
path = req.get_param('path', required=True)
sort = req.get_param('sort', default='modified')
reverse = req.get_param('reverse', default=False)
# Convert arguments if a specific type is required
reverse = reverse == 'True'
# Here we actually do stuff
try:
result = [f.to_dict for f in files.list(path, sort, reverse)]
except OSError:
raise falcon.HTTPNotFound('No path {}'.format(path))
# When all ready, prepare the response
result_string = json.dumps(result)
resp.status = falcon.HTTP_200
resp.body = result_string
resp.content_type = 'application/json'
Falcon Application Example (cont.)

WSGI Deficiencies
To do the same work: Different framework == different application
Once you choose a framework, you are locked in!
Server/
Gateway
Application2
Application1
Application3
WSGI
API 1
API 2
API 3
Application4
API 4

REST Frameworks: Same Same but Different
Same same But Different
Methods that do
something with request
and response objects.
● Some accept request and response objects.
● Some accept requests and return responses.
● Some magically have the request.
● Some accept URL arguments.
● Some convert return value to a response.
● Some can read/write from the resource class methods.
Register of Python
methods/classes on URLs.
● Some use resource classes.
● Some use resource methods.
● Some use both.
● For some the class is only for a specific URL, for some it is for a
resource.

REST Frameworks: Same Same but Different (cont)
Same same But Different
Error handling ● Some catch a specific exception types.
● Some need a response object returned.
Their own
Request/Response object
They were made for web
serving
With REST extensions.

Hammock

Hammock
1. Abstraction
2. Built for REST & developer friendly
3. Many cool features

1. Hammock Abstraction
ApplicationHammock
Server/
Gateway

Hammock Abstraction
Server/
Gateway
Well… to be honest....
ApplicationHammock
WIP

2. Ease of Use: Handlers
class Files(hammock.Resource):
@hammock.get('/')
def list(self, path, sort='modified', reverse=False, type=None):
"""
List files in directory.
:param str path: Path to list files in.
:param str type: Show only files of type.
:param str sort: Sort files by attribute
:param bool[False] reverse: Sort reverse.
:return list: List of files.
"""
try:
return [f.to_dict for f in files.list(path, sort, reverse)]
except OSError:
raise exceptions.NotFound('No path {}'.format(path))
@hammock.get('/{file_id}')
def get(self, file_id)
...
Don't worry about
converting requests to
arguments.
Don't worry about
converting results to
responses.
Simply write
Python
functions

2. Ease of Use: Some Corner Cases
Hammock has some reserved arguments.
# streams
@hammock.post()
def func(self, _file): # get octet/stream
return open(‘path’, ‘r’) # return octet/stream
# headers
@hammock.post()
def func(self, _headers): # get headers
return {‘_headers’: {‘key1’: ‘value1’}} # return headers
# when request body is a list
@hammock.post()
def func(self, _list): # get a list body
return [] # return list

2. Ease of Use: Resource Registering
Use a package structure to build URLs:
resources/
hotels/
hotels.py /hotels
rooms/
rooms.py /hotels/{hotel_id}/rooms
reservations.py /hotels/{hotel_id}/rooms/{room_id}/reservations
customers.py /customers

3. Many COOL Features
Hammock
Free Python
client!
Free CLIAuthorization
enforcement
Free API
documentation

How does it work?? At Server Startup:
app = hammock.Hammock(‘falcon’, resources)
❏ Iterate over a 'resources' package,
collect all decorated route methods
into a dict:
{path: {method: function}}
❏ Register handlers using a backend API.
❏ The handler is a translator between backend
handler to the function.
def on_post(self, req, resp):
...
class File(object):
def on_get(self, req, resp, file_id):
...
app.add_route('/files', Files())
app.add_route('/files/{file_id}', File())

How does it work?? Upon request:
Backend
Request
Backend
Response
Hammock
Request
Hammock
Response
Method
Arguments
Method
Result
Backend
Framework
Decorated
Method
There is a lot of magic there...

Future work
❏ More frameworks! (maybe you wanna help?)
❏ Scheme validation.
❏ Combine with swagger/RAML.
❏ Improve unit testing infra.
❏ And much more :-)

Questions?
❏ Contact:
eyal@stratoscale.com
❏ Install:
pip install hammock-rest
>>> import hammock
❏ Contribute:
git clone https://github.com/Stratoscale/hammock.git

Performance
Property Falcon Hammock Ratio Remarks
Document Length [bytes] 638 601 1.06 ujson :-)
Time taken for tests [seconds] 36.3 38 0.96
Requests per second [#/sec] (mean) 1378.5 1314.6 1.05
Time per request [ms] (mean) 0.725 0.761 0.95
Transfer rate [Kbytes/sec] received 955.8 864 1.11
Small benchmark with Apache bench for 50,000 GET requests that returns the
same file list method.

WSGI
def app(environ, start_response):
start_response('200 OK', [('Content-type', 'text/plain')])
return ['Hello world!n']

Appendix
List of WSGI compliant servers.
List of WSGI compliant frameworks.

Hammock, a Good Place to Rest

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