parfait 0.3
Microframework
License: Apache License 2.0
Keywords: chalice,parfait,aws,lambda,amazon web services

========================================
Python Serverless Microframework for AWS
========================================

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Chalice is a microframework for writing serverless apps in python. It allows
you to quickly create and deploy applications that use AWS Lambda.  It provides:

* A command line tool for creating, deploying, and managing your app
* A decorator based API for integrating with Amazon API Gateway, Amazon S3,
  Amazon SNS, Amazon SQS, and other AWS services.
* Automatic IAM policy generation


You can create Rest APIs:

.. code-block:: python

    from chalice import Chalice

    app = Chalice(app_name="helloworld")

    @app.route("/")
    def index():
        return {"hello": "world"}

Tasks that run on a periodic basis:

.. code-block:: python

    from chalice import Chalice, Rate

    app = Chalice(app_name="helloworld")

    # Automatically runs every 5 minutes
    @app.schedule(Rate(5, unit=Rate.MINUTES))
    def periodic_task(event):
        return {"hello": "world"}


You can connect a lambda function to an S3 event:

.. code-block:: python

    from chalice import Chalice

    app = Chalice(app_name="helloworld")

    # Whenever an object is uploaded to 'mybucket'
    # this lambda function will be invoked.

    @app.on_s3_event(bucket='mybucket')
    def handler(event):
        print("Object uploaded for bucket: %s, key: %s"
              % (event.bucket, event.key))

As well as an SQS queue:

.. code-block:: python

    from chalice import Chalice

    app = Chalice(app_name="helloworld")

    # Invoke this lambda function whenever a message
    # is sent to the ``my-queue-name`` SQS queue.

    @app.on_sqs_message(queue='my-queue-name')
    def handler(event):
        for record in event:
            print("Message body: %s" % record.body)


And several other AWS resources.

Once you've written your code, you just run ``chalice deploy``
and Chalice takes care of deploying your app.

::

    $ chalice deploy
    ...
    https://endpoint/dev

    $ curl https://endpoint/api
    {"hello": "world"}

Up and running in less than 30 seconds.
Give this project a try and share your feedback with us here on Github.

The documentation is available
`on readthedocs <http://chalice.readthedocs.io/en/latest/>`__.

Quickstart
==========

.. quick-start-begin

In this tutorial, you'll use the ``chalice`` command line utility
to create and deploy a basic REST API.
First, you'll need to install ``chalice``.  Using a virtualenv
is recommended::

    $ pip install virtualenv
    $ virtualenv ~/.virtualenvs/chalice-demo
    $ source ~/.virtualenvs/chalice-demo/bin/activate

Note: **make sure you are using python2.7, python3.6, or python3.7**.
These are the only python versions currently supported by AWS Lambda so they
are also the only versions supported by the ``chalice`` CLI and ``chalice``
python package. You can check the version of python in your virtualenv by
running::

    # Double check you have a supported python version in your virtualenv
    $ python -V

Next, in your virtualenv, install ``chalice``::

    $ pip install chalice

You can verify you have chalice installed by running::

    $ chalice --help
    Usage: chalice [OPTIONS] COMMAND [ARGS]...
    ...


Credentials
-----------

Before you can deploy an application, be sure you have
credentials configured.  If you have previously configured your
machine to run boto3 (the AWS SDK for Python) or the AWS CLI then
you can skip this section.

If this is your first time configuring credentials for AWS you
can follow these steps to quickly get started::

    $ mkdir ~/.aws
    $ cat >> ~/.aws/config
    [default]
    aws_access_key_id=YOUR_ACCESS_KEY_HERE
    aws_secret_access_key=YOUR_SECRET_ACCESS_KEY
    region=YOUR_REGION (such as us-west-2, us-west-1, etc)

If you want more information on all the supported methods for
configuring credentials, see the
`boto3 docs
<http://boto3.readthedocs.io/en/latest/guide/configuration.html>`__.


Creating Your Project
---------------------

The next thing we'll do is use the ``chalice`` command to create a new
project::

    $ chalice new-project helloworld

This will create a ``helloworld`` directory.  Cd into this
directory.  You'll see several files have been created for you::

    $ cd helloworld
    $ ls -la
    drwxr-xr-x   .chalice
    -rw-r--r--   app.py
    -rw-r--r--   requirements.txt

You can ignore the ``.chalice`` directory for now, the two main files
we'll focus on is ``app.py`` and ``requirements.txt``.

Let's take a look at the ``app.py`` file:

.. code-block:: python

    from chalice import Chalice

    app = Chalice(app_name='helloworld')


    @app.route('/')
    def index():
        return {'hello': 'world'}


The ``new-project`` command created a sample app that defines a
single view, ``/``, that when called will return the JSON body
``{"hello": "world"}``.


Deploying
---------

Let's deploy this app.  Make sure you're in the ``helloworld``
directory and run ``chalice deploy``::

    $ chalice deploy
    ...
    Initiating first time deployment...
    https://qxea58oupc.execute-api.us-west-2.amazonaws.com/api/

You now have an API up and running using API Gateway and Lambda::

    $ curl https://qxea58oupc.execute-api.us-west-2.amazonaws.com/api/
    {"hello": "world"}

Try making a change to the returned dictionary from the ``index()``
function.  You can then redeploy your changes by running ``chalice deploy``.


For the rest of these tutorials, we'll be using ``httpie`` instead of ``curl``
(https://github.com/jakubroztocil/httpie) to test our API.  You can install
``httpie`` using ``pip install httpie``, or if you're on Mac, you can run
``brew install httpie``.  The Github link has more information on installation
instructions.  Here's an example of using ``httpie`` to request the root
resource of the API we just created.  Note that the command name is ``http``::


    $ http https://qxea58oupc.execute-api.us-west-2.amazonaws.com/api/
    HTTP/1.1 200 OK
    Connection: keep-alive
    Content-Length: 18
    Content-Type: application/json
    Date: Mon, 30 May 2016 17:55:50 GMT
    X-Cache: Miss from cloudfront

    {
        "hello": "world"
    }


Additionally, the API Gateway endpoints will be shortened to
``https://endpoint/api/`` for brevity.  Be sure to substitute
``https://endpoint/api/`` for the actual endpoint that the ``chalice``
CLI displays when you deploy your API (it will look something like
``https://abcdefg.execute-api.us-west-2.amazonaws.com/api/``.

Next Steps
----------

You've now created your first app using ``chalice``.

The next few sections will build on this quickstart section and introduce
you to additional features including: URL parameter capturing,
error handling, advanced routing, current request metadata, and automatic
policy generation.


Tutorial: URL Parameters
========================

Now we're going to make a few changes to our ``app.py`` file that
demonstrate additional capabilities provided by the python serverless
microframework for AWS.

Our application so far has a single view that allows you to make
an HTTP GET request to ``/``.  Now let's suppose we want to capture
parts of the URI:

.. code-block:: python

    from chalice import Chalice

    app = Chalice(app_name='helloworld')

    CITIES_TO_STATE = {
        'seattle': 'WA',
        'portland': 'OR',
    }


    @app.route('/')
    def index():
        return {'hello': 'world'}

    @app.route('/cities/{city}')
    def state_of_city(city):
        return {'state': CITIES_TO_STATE[city]}


In the example above, we've now added a ``state_of_city`` view that allows
a user to specify a city name.  The view function takes the city
name and returns name of the state the city is in.  Notice that the
``@app.route`` decorator has a URL pattern of ``/cities/{city}``.  This
means that the value of ``{city}`` is captured and passed to the view
function.  You can also see that the ``state_of_city`` takes a single
argument.  This argument is the name of the city provided by the user.
For example::

    GET /cities/seattle   --> state_of_city('seattle')
    GET /cities/portland  --> state_of_city('portland')

Now that we've updated our ``app.py`` file with this new view function,
let's redeploy our application.  You can run ``chalice deploy`` from
the ``helloworld`` directory and it will deploy your application::

    $ chalice deploy

Let's try it out.  Note the examples below use the ``http`` command
from the ``httpie`` package.  You can install this using ``pip install httpie``::

    $ http https://endpoint/api/cities/seattle
    HTTP/1.1 200 OK

    {
        "state": "WA"
    }

    $ http https://endpoint/api/cities/portland
    HTTP/1.1 200 OK

    {
        "state": "OR"
    }


Notice what happens if we try to request a city that's not in our
``CITIES_TO_STATE`` map::

    $ http https://endpoint/api/cities/vancouver
    HTTP/1.1 500 Internal Server Error
    Content-Type: application/json
    X-Cache: Error from cloudfront

    {
        "Code": "ChaliceViewError",
        "Message": "ChaliceViewError: An internal server error occurred."
    }


In the next section, we'll see how to fix this and provide better
error messages.


Tutorial: Error Messages
========================

In the example above, you'll notice that when our app raised
an uncaught exception, a 500 internal server error was returned.

In this section, we're going to show how you can debug and improve
these error messages.

The first thing we're going to look at is how we can debug this
issue.  By default, debugging is turned off, but you can
enable debugging to get more information:

.. code-block:: python

    from chalice import Chalice

    app = Chalice(app_name='helloworld')
    app.debug = True


The ``app.debug = True`` enables debugging for your app.
Save this file and redeploy your changes::

    $ chalice deploy
    ...
    https://endpoint/api/

Now, when you request the same URL that returned an internal
server error, you'll get back the original stack trace::

    $ http https://endpoint/api/cities/vancouver
    Traceback (most recent call last):
      File "/var/task/chalice/app.py", line 304, in _get_view_function_response
        response = view_function(*function_args)
      File "/var/task/app.py", line 18, in state_of_city
        return {'state': CITIES_TO_STATE[city]}
    KeyError: u'vancouver'


We can see that the error is caused from an uncaught ``KeyError`` resulting
from trying to access the ``vancouver`` key.

Now that we know the error, we can fix our code.  What we'd like to do is
catch this exception and instead return a more helpful error message
to the user.  Here's the updated code:

.. code-block:: python

    from chalice import BadRequestError

    @app.route('/cities/{city}')
    def state_of_city(city):
        try:
            return {'state': CITIES_TO_STATE[city]}
        except KeyError:
            raise BadRequestError("Unknown city '%s', valid choices are: %s" % (
                city, ', '.join(CITIES_TO_STATE.keys())))


Save and deploy these changes::

    $ chalice deploy
    $ http https://endpoint/api/cities/vancouver
    HTTP/1.1 400 Bad Request

    {
        "Code": "BadRequestError",
        "Message": "Unknown city 'vancouver', valid choices are: portland, seattle"
    }

We can see now that we have received a ``Code`` and ``Message`` key, with the message
being the value we passed to ``BadRequestError``.  Whenever you raise
a ``BadRequestError`` from your view function, the framework will return an
HTTP status code of 400 along with a JSON body with a ``Code`` and ``Message``.
There are a few additional exceptions you can raise from your python code::

* BadRequestError - return a status code of 400
* UnauthorizedError - return a status code of 401
* ForbiddenError - return a status code of 403
* NotFoundError - return a status code of 404
* ConflictError - return a status code of 409
* UnprocessableEntityError - return a status code of 422
* TooManyRequestsError - return a status code of 429
* ChaliceViewError - return a status code of 500

You can import these directly from the ``chalice`` package:

.. code-block:: python

    from chalice import UnauthorizedError


Tutorial: Additional Routing
============================

So far, our examples have only allowed GET requests.
It's actually possible to support additional HTTP methods.
Here's an example of a view function that supports PUT:

.. code-block:: python

    @app.route('/resource/{value}', methods=['PUT'])
    def put_test(value):
        return {"value": value}

We can test this method using the ``http`` command::

    $ http PUT https://endpoint/api/resource/foo
    HTTP/1.1 200 OK

    {
        "value": "foo"
    }

Note that the ``methods`` kwarg accepts a list of methods.  Your view function
will be called when any of the HTTP methods you specify are used for the
specified resource.  For example:

.. code-block:: python

    @app.route('/myview', methods=['POST', 'PUT'])
    def myview():
        pass

The above view function will be called when either an HTTP POST or
PUT is sent to ``/myview``.

Alternatively if you do not want to share the same view function across
multiple HTTP methods for the same route url, you may define separate view
functions to the same route url but have the view functions differ by
HTTP method. For example:

.. code-block:: python

    @app.route('/myview', methods=['POST'])
    def myview_post():
        pass

    @app.route('/myview', methods=['PUT'])
    def myview_put():
        pass

This setup will route all HTTP POST's to ``/myview`` to the ``myview_post()``
view function and route all HTTP PUT's to ``/myview`` to the ``myview_put()``
view function. It is also important to note that the view functions
**must** have unique names. For example, both view functions cannot be
named ``myview()``.

In the next section we'll go over how you can introspect the given request
in order to differentiate between various HTTP methods.


Tutorial: Request Metadata
==========================

In the examples above, you saw how to create a view function that supports
an HTTP PUT request as well as a view function that supports both POST and
PUT via the same view function.  However, there's more information we
might need about a given request:

* In a PUT/POST, you frequently send a request body.  We need some
  way of accessing the contents of the request body.
* For view functions that support multiple HTTP methods, we'd like
  to detect which HTTP method was used so we can have different
  code paths for PUTs vs. POSTs.

All of this and more is handled by the current request object that the
``chalice`` library makes available to each view function when it's called.

Let's see an example of this.  Suppose we want to create a view function
that allowed you to PUT data to an object and retrieve that data
via a corresponding GET.  We could accomplish that with the
following view function:

.. code-block:: python

    from chalice import NotFoundError

    OBJECTS = {
    }

    @app.route('/objects/{key}', methods=['GET', 'PUT'])
    def myobject(key):
        request = app.current_request
        if request.method == 'PUT':
            OBJECTS[key] = request.json_body
        elif request.method == 'GET':
            try:
                return {key: OBJECTS[key]}
            except KeyError:
                raise NotFoundError(key)


Save this in your ``app.py`` file and rerun ``chalice deploy``.
Now, you can make a PUT request to ``/objects/your-key`` with a request
body, and retrieve the value of that body by making a subsequent
``GET`` request to the same resource.  Here's an example of its usage::

    # First, trying to retrieve the key will return a 404.
    $ http GET https://endpoint/api/objects/mykey
    HTTP/1.1 404 Not Found

    {
        "Code": "NotFoundError",
        "Message": "mykey"
    }

    # Next, we'll create that key by sending a PUT request.
    $ echo '{"foo": "bar"}' | http PUT https://endpoint/api/objects/mykey
    HTTP/1.1 200 OK

    null

    # And now we no longer get a 404, we instead get the value we previously
    # put.
    $ http GET https://endpoint/api/objects/mykey
    HTTP/1.1 200 OK

    {
        "mykey": {
            "foo": "bar"
        }
    }

You might see a problem with storing the objects in a module level
``OBJECTS`` variable.  We address this in the next section.

The ``app.current_request`` object also has the following properties.

* ``current_request.query_params`` - A dict of the query params for the request.
* ``current_request.headers`` - A dict of the request headers.
* ``current_request.uri_params`` - A dict of the captured URI params.
* ``current_request.method`` -  The HTTP method (as a string).
* ``current_request.json_body`` - The parsed JSON body (``json.loads(raw_body)``)
* ``current_request.raw_body`` - The raw HTTP body as bytes.
* ``current_request.context`` - A dict of additional context information
* ``current_request.stage_vars`` - Configuration for the API Gateway stage

Don't worry about the ``context`` and ``stage_vars`` for now.  We haven't
discussed those concepts yet.  The ``current_request`` object also
has a ``to_dict`` method, which returns all the information about the
current request as a dictionary.  Let's use this method to write a view
function that returns everything it knows about the request:

.. code-block:: python

    @app.route('/introspect')
    def introspect():
        return app.current_request.to_dict()


Save this to your ``app.py`` file and redeploy with ``chalice deploy``.
Here's an example of hitting the ``/introspect`` URL.  Note how we're
sending a query string as well as a custom ``X-TestHeader`` header::


    $ http 'https://endpoint/api/introspect?query1=value1&query2=value2' 'X-TestHeader: Foo'
    HTTP/1.1 200 OK

    {
        "context": {
            "apiId": "apiId",
            "httpMethod": "GET",
            "identity": {
                "accessKey": null,
                "accountId": null,
                "apiKey": null,
                "caller": null,
                "cognitoAuthenticationProvider": null,
                "cognitoAuthenticationType": null,
                "cognitoIdentityId": null,
                "cognitoIdentityPoolId": null,
                "sourceIp": "1.1.1.1",
                "userAgent": "HTTPie/0.9.3",
                "userArn": null
            },
            "requestId": "request-id",
            "resourceId": "resourceId",
            "resourcePath": "/introspect",
            "stage": "dev"
        },
        "headers": {
            "accept": "*/*",
            ...
            "x-testheader": "Foo"
        },
        "method": "GET",
        "query_params": {
            "query1": "value1",
            "query2": "value2"
        },
        "raw_body": null,
        "stage_vars": null,
        "uri_params": null
    }


Tutorial: Request Content Types
===============================

The default behavior of a view function supports
a request body of ``application/json``.  When a request is
made with a ``Content-Type`` of ``application/json``, the
``app.current_request.json_body`` attribute is automatically
set for you.  This value is the parsed JSON body.

You can also configure a view function to support other
content types.  You can do this by specifying the
``content_types`` parameter value to your ``app.route``
function.  This parameter is a list of acceptable content
types.  Here's an example of this feature:

.. code-block:: python

    import sys

    from chalice import Chalice
    if sys.version_info[0] == 3:
        # Python 3 imports.
        from urllib.parse import urlparse, parse_qs
    else:
        # Python 2 imports.
        from urlparse import urlparse, parse_qs


    app = Chalice(app_name='helloworld')


    @app.route('/', methods=['POST'],
               content_types=['application/x-www-form-urlencoded'])
    def index():
        parsed = parse_qs(app.current_request.raw_body.decode())
        return {
            'states': parsed.get('states', [])
        }

There's a few things worth noting in this view function.
First, we've specified that we only accept the
``application/x-www-form-urlencoded`` content type.  If we
try to send a request with ``application/json``, we'll now
get a ``415 Unsupported Media Type`` response::

    $ http POST https://endpoint/api/ states=WA states=CA --debug
    ...
    >>> requests.request(**{'allow_redirects': False,
     'headers': {'Accept': 'application/json',
                 'Content-Type': 'application/json',
    ...


    HTTP/1.1 415 Unsupported Media Type

    {
        "message": "Unsupported Media Type"
    }

If we use the ``--form`` argument, we can see the
expected behavior of this view function because ``httpie`` sets the
``Content-Type`` header to ``application/x-www-form-urlencoded``::

    $ http --form POST https://endpoint/api/formtest states=WA states=CA --debug
    ...
    >>> requests.request(**{'allow_redirects': False,
     'headers': {'Content-Type': 'application/x-www-form-urlencoded; charset=utf-8',
    ...

    HTTP/1.1 200 OK
    {
        "states": [
            "WA",
            "CA"
        ]
    }

The second thing worth noting is that ``app.current_request.json_body``
**is only available for the application/json content type.**
In our example above, we used ``app.current_request.raw_body`` to access
the raw body bytes:

.. code-block:: python

    parsed = parse_qs(app.current_request.raw_body)

``app.current_request.json_body`` is set to ``None`` whenever the
``Content-Type`` is not ``application/json``.  This means that
you will need to use ``app.current_request.raw_body`` and parse
the request body as needed.


Tutorial: Customizing the HTTP Response
=======================================

The return value from a chalice view function is serialized as JSON as the
response body returned back to the caller.  This makes it easy to create
rest APIs that return JSON response bodies.

Chalice allows you to control this behavior by returning an instance of
a chalice specific ``Response`` class.  This behavior allows you to:

* Specify the status code to return
* Specify custom headers to add to the response
* Specify response bodies that are not ``application/json``

Here's an example of this:

.. code-block:: python

    from chalice import Chalice, Response

    app = Chalice(app_name='custom-response')


    @app.route('/')
    def index():
        return Response(body='hello world!',
                        status_code=200,
                        headers={'Content-Type': 'text/plain'})

This will result in a plain text response body::

    $ http https://endpoint/api/
    HTTP/1.1 200 OK
    Content-Length: 12
    Content-Type: text/plain

    hello world!


Tutorial: GZIP compression for json
===================================
The return value from a chalice view function is serialized as JSON as the
response body returned back to the caller.  This makes it easy to create
rest APIs that return JSON response bodies.

Chalice allows you to control this behavior by returning an instance of
a chalice specific ``Response`` class.  This behavior allows you to:

* Add ``application/json`` to binary_types
* Specify the status code to return
* Specify custom header ``Content-Type: application/json``
* Specify custom header ``Content-Encoding: gzip``

Here's an example of this:

.. code-block:: python

    import json
    import gzip
    from chalice import Chalice, Response

    app = Chalice(app_name='compress-response')
    app.api.binary_types.append('application/json')

    @app.route('/')
    def index():
        blob = json.dumps({'hello': 'world'}).encode('utf-8')
        payload = gzip.compress(blob)
        custom_headers = {
            'Content-Type': 'application/json',
            'Content-Encoding': 'gzip'
        }
        return Response(body=payload,
                        status_code=200,
                        headers=custom_headers)



Tutorial: CORS Support
======================

You can specify whether a view supports CORS by adding the
``cors=True`` parameter to your ``@app.route()`` call.  By
default this value is false:

.. code-block:: python

    @app.route('/supports-cors', methods=['PUT'], cors=True)
    def supports_cors():
        return {}


Settings ``cors=True`` has similar behavior to enabling CORS
using the AWS Console.  This includes:

* Injecting the ``Access-Control-Allow-Origin: *`` header to your
  responses, including all error responses you can return.
* Automatically adding an ``OPTIONS`` method to support preflighting
  requests.

The preflight request will return a response that includes:

* ``Access-Control-Allow-Origin: *``
* The ``Access-Control-Allow-Methods`` header will return a list of all HTTP
  methods you've called out in your view function.  In the example above,
  this will be ``PUT,OPTIONS``.
* ``Access-Control-Allow-Headers: Content-Type,X-Amz-Date,Authorization,
  X-Api-Key,X-Amz-Security-Token``.

If more fine grained control of the CORS headers is desired, set the ``cors``
parameter to an instance of ``CORSConfig`` instead of ``True``. The
``CORSConfig`` object can be imported from from the ``chalice`` package it's
constructor takes the following keyword arguments that map to CORS headers:

================= ==== ================================
Argument          Type Header
================= ==== ================================
allow_origin      str  Access-Control-Allow-Origin
allow_headers     list Access-Control-Allow-Headers
expose_headers    list Access-Control-Expose-Headers
max_age           int  Access-Control-Max-Age
allow_credentials bool Access-Control-Allow-Credentials
================= ==== ================================

Code sample defining more CORS headers:

.. code-block:: python

    from chalice import CORSConfig
    cors_config = CORSConfig(
        allow_origin='https://foo.example.com',
        allow_headers=['X-Special-Header'],
        max_age=600,
        expose_headers=['X-Special-Header'],
        allow_credentials=True
    )
    @app.route('/custom_cors', methods=['GET'], cors=cors_config)
    def supports_custom_cors():
        return {'cors': True}


There's a couple of things to keep in mind when enabling cors for a view:

* An ``OPTIONS`` method for preflighting is always injected.  Ensure that
  you don't have ``OPTIONS`` in the ``methods=[...]`` list of your
  view function.
* Even though the ``Access-Control-Allow-Origin`` header can be set to a
  string that is a space separated list of origins, this behavior does not
  work on all clients that implement CORS. You should only supply a single
  origin to the ``CORSConfig`` object. If you need to supply multiple origins
  you will need to define a custom handler for it that accepts ``OPTIONS``
  requests and matches the ``Origin`` header against a whitelist of origins.
  If the match is successful then return just their ``Origin`` back to them
  in the ``Access-Control-Allow-Origin`` header.

  Example:

.. code-block:: python

    from chalice import Chalice, Response

    app = Chalice(app_name='multipleorigincors')

    _ALLOWED_ORIGINS = set([
	'http://allowed1.example.com',
	'http://allowed2.example.com',
    ])


    @app.route('/cors_multiple_origins', methods=['GET', 'OPTIONS'])
    def supports_cors_multiple_origins():
	method = app.current_request.method
	if method == 'OPTIONS':
	    headers = {
		'Access-Control-Allow-Method': 'GET,OPTIONS',
		'Access-Control-Allow-Origin': ','.join(_ALLOWED_ORIGINS),
		'Access-Control-Allow-Headers': 'X-Some-Header',
	    }
	    origin = app.current_request.headers.get('origin', '')
	    if origin in _ALLOWED_ORIGINS:
		headers.update({'Access-Control-Allow-Origin': origin})
	    return Response(
		body=None,
		headers=headers,
	    )
	elif method == 'GET':
	    return 'Foo'

* Every view function must explicitly enable CORS support.

The last point will change in the future.  See
`this issue
<https://github.com/aws/chalice/issues/70#issuecomment-248787037>`_
for more information.


Tutorial: Policy Generation
===========================

In the previous section we created a basic rest API that
allowed you to store JSON objects by sending the JSON
in the body of an HTTP PUT request to ``/objects/{name}``.
You could then retrieve objects by sending a GET request to
``/objects/{name}``.

However, there's a problem with the code we wrote:

.. code-block:: python

    OBJECTS = {
    }

    @app.route('/objects/{key}', methods=['GET', 'PUT'])
    def myobject(key):
        request = app.current_request
        if request.method == 'PUT':
            OBJECTS[key] = request.json_body
        elif request.method == 'GET':
            try:
                return {key: OBJECTS[key]}
            except KeyError:
                raise NotFoundError(key)


We're storing the key value pairs in a module level ``OBJECTS``
variable.  We can't rely on local storage like this persisting
across requests.

A better solution would be to store this information in Amazon S3.
To do this, we're going to use boto3, the AWS SDK for Python.
First, install boto3::

    $ pip install boto3

Next, add ``boto3`` to your requirements.txt file::

    $ echo 'boto3==1.3.1' >> requirements.txt

The requirements.txt file should be in the same directory that contains
your ``app.py`` file.  Next, let's update our view code to use boto3:

.. code-block:: python

    import json
    import boto3
    from botocore.exceptions import ClientError

    from chalice import NotFoundError


    S3 = boto3.client('s3', region_name='us-west-2')
    BUCKET = 'your-bucket-name'


    @app.route('/objects/{key}', methods=['GET', 'PUT'])
    def s3objects(key):
        request = app.current_request
        if request.method == 'PUT':
            S3.put_object(Bucket=BUCKET, Key=key,
                          Body=json.dumps(request.json_body))
        elif request.method == 'GET':
            try:
                response = S3.get_object(Bucket=BUCKET, Key=key)
                return json.loads(response['Body'].read())
            except ClientError as e:
                raise NotFoundError(key)

Make sure to change ``BUCKET`` with the name of an S3 bucket
you own.  Redeploy your changes with ``chalice deploy``.
Now, whenever we make a ``PUT`` request to ``/objects/keyname``, the
data send will be stored in S3.  Any subsequent ``GET`` requests will
retrieve this data from S3.

Manually Providing Policies
---------------------------


IAM permissions can be auto generated, provided manually or can be
pre-created and explicitly configured. To use a
pre-configured IAM role ARN for chalice, add these two keys to your
chalice configuration. Setting manage_iam_role to false tells
Chalice to not attempt to generate policies and create IAM role.

::

    "manage_iam_role":false
    "iam_role_arn":"arn:aws:iam::<account-id>:role/<role-name>"

Whenever your application is deployed using ``chalice``, the
auto generated policy is written to disk at
``<projectdir>/.chalice/policy.json``.  When you run the
``chalice deploy`` command, you can also specify the
``--no-autogen-policy`` option.  Doing so will result in the
``chalice`` CLI loading the ``<projectdir>/.chalice/policy.json``
file and using that file as the policy for the IAM role.
You can manually edit this file and specify ``--no-autogen-policy``
if you'd like to have full control over what IAM policy to associate
with the IAM role.

You can also run the ``chalice gen-policy`` command from your project
directory to print the auto generated policy to stdout.  You can
then use this as a starting point for your policy.

::

    $ chalice gen-policy
    {
      "Version": "2012-10-17",
      "Statement": [
        {
          "Action": [
            "s3:ListAllMyBuckets"
          ],
          "Resource": [
            "*"
          ],
          "Effect": "Allow",
          "Sid": "9155de6ad1d74e4c8b1448255770e60c"
        }
      ]
    }

Experimental Status
-------------------

The automatic policy generation is still in the early stages, it should
be considered experimental.  You can always disable policy
generation with ``--no-autogen-policy`` for complete control.

Additionally, you will be prompted for confirmation whenever the
auto policy generator detects actions that it would like to add or remove::


    $ chalice deploy
    Updating IAM policy.

    The following action will be added to the execution policy:

    s3:ListBucket

    Would you like to continue?  [Y/n]:


Tutorial: Using Custom Authentication
=====================================

AWS API Gateway routes can be authenticated in multiple ways:

- API Key
- AWS IAM
- Cognito User Pools
- Custom Auth Handler

API Key
-------

.. code-block:: python

    @app.route('/authenticated', methods=['GET'], api_key_required=True)
    def authenticated():
        return {"secure": True}

Only requests sent with a valid `X-Api-Key` header will be accepted.

Using AWS IAM
-------------

.. code-block:: python

    authorizer = IAMAuthorizer()

    @app.route('/iam-role', methods=['GET'], authorizer=authorizer)
    def authenticated():
        return {"secure": True}


Using Amazon Cognito User Pools
-------------------------------

To integrate with cognito user pools, you can use the
``CognitoUserPoolAuthorizer`` object:

.. code-block:: python

    authorizer = CognitoUserPoolAuthorizer(
        'MyPool', header='Authorization',
        provider_arns=['arn:aws:cognito:...:userpool/name'])

    @app.route('/user-pools', methods=['GET'], authorizer=authorizer)
    def authenticated():
        return {"secure": True}


Note, earlier versions of chalice also have an ``app.define_authorizer``
method as well as an ``authorizer_name`` argument on the ``@app.route(...)``
method.  This approach is deprecated in favor of ``CognitoUserPoolAuthorizer``
and the ``authorizer`` argument in the ``@app.route(...)`` method.
``app.define_authorizer`` will be removed in future versions of chalice.


Using Custom Authorizers
------------------------

To integrate with custom authorizers, you can use the ``CustomAuthorizer`` method
on the ``app`` object.  You'll need to set the ``authorizer_uri``
to the URI of your lambda function.

.. code-block:: python

    authorizer = CustomAuthorizer(
        'MyCustomAuth', header='Authorization',
        authorizer_uri=('arn:aws:apigateway:region:lambda:path/2015-03-31'
                        '/functions/arn:aws:lambda:region:account-id:'
                        'function:FunctionName/invocations'))

    @app.route('/custom-auth', methods=['GET'], authorizer=authorizer)
    def authenticated():
        return {"secure": True}


Tutorial: Local Mode
====================

As you develop your application, you may want to experiment locally  before
deploying your changes.  You can use ``chalice local`` to spin up a local
HTTP server you can use for testing.

For example, if we have the following ``app.py`` file:

.. code-block:: python

    from chalice import Chalice

    app = Chalice(app_name='helloworld')


    @app.route('/')
    def index():
        return {'hello': 'world'}


We can run ``chalice local`` to test this API locally:


    $ chalice local
    Serving on localhost:8000

We can override the port using:

    $ chalice local --port=8080

We can now test our API using ``localhost:8000``::

    $ http localhost:8000/
    HTTP/1.0 200 OK
    Content-Length: 18
    Content-Type: application/json
    Date: Thu, 27 Oct 2016 20:08:43 GMT
    Server: BaseHTTP/0.3 Python/2.7.11

    {
        "hello": "world"
    }


The ``chalice local`` command *does not* assume the
role associated with your lambda function, so you'll
need to use an ``AWS_PROFILE`` that has sufficient permissions
to your AWS resources used in your ``app.py``.


Deleting Your App
=================

You can use the ``chalice delete`` command to delete your app.
Similar to the ``chalice deploy`` command, you can specify which
chalice stage to delete.  By default it will delete the ``dev`` stage::

    $ chalice delete --stage dev
    Deleting Rest API: duvw4kwyl3
    Deleting function aws:arn:lambda:region:123456789:helloworld-dev
    Deleting IAM Role helloworld-dev

.. quick-start-end

Feedback
========

We'also love to hear from you.  Please create any Github issues for
additional features you'd like to see over at
https://github.com/aws/chalice/issues.  You can also chat with us
on gitter: https://gitter.im/awslabs/chalice


FAQ
===


**Q: How does the Python Serverless Microframework for AWS compare to other
similar frameworks?**

The biggest difference between this framework and others is that the Python
Serverless Microframework for AWS is singularly focused on using a familiar,
decorator-based API to write python applications that run on Amazon API Gateway
and AWS Lambda.  You can think of it as
`Flask <http://flask.pocoo.org/>`__/`Bottle <http://bottlepy.org/docs/dev/index.html>`__
for serverless APIs.  Its goal is to make writing and deploying these types of
applications as simple as possible specifically for Python developers.

To achieve this goal, it has to make certain tradeoffs.  Python will always
remain the only supported language in this framework.  Not every feature of API
Gateway and Lambda is exposed in the framework.  It makes assumptions about how
applications will be deployed, and it has restrictions on how an application
can be structured.  It does not address the creation and lifecycle of other AWS
resources your application may need (Amazon S3 buckets, Amazon DynamoDB tables,
etc.).  The feature set is purposefully small.

Other full-stack frameworks offer a lot more features and configurability than
what this framework has and likely will ever have.  Those frameworks are
excellent choices for applications that need more than what is offered by this
microframework.  If all you need is to create a simple rest API in Python that
runs on Amazon API Gateway and AWS Lambda, consider giving the Python
Serverless Microframework for AWS a try.

Related Projects
----------------

* `serverless <https://github.com/serverless/serverless>`__ - Build applications
  comprised of microservices that run in response to events, auto-scale for
  you, and only charge you when they run.
* `Zappa <https://github.com/Miserlou/Zappa>`__ - Deploy python WSGI applications
  on AWS Lambda and API Gateway.
* `claudia <https://github.com/claudiajs/claudia>`__ - Deploy node.js projects
  to AWS Lambda and API Gateway.
* `Domovoi <https://github.com/kislyuk/domovoi>`_ - An extension to Chalice that
  handles a variety of AWS Lambda event sources such as SNS push notifications,
  S3 events, and Step Functions state machines.