Chalice: AWS Lambda使ったアプリが簡単に作れるPythonライブラリ
Boto3: S3にアクセスするためのPythonライブラリ

以下のような構成で、S3からjsonデータを取得したり、保存したりできるアプリを作ります

WebBrowser -- AWS (API Gateway -- Lambda -- S3)

POST /api/save/ : S3にjsonデータを保存
GET /api/load/{key} : S3からjsonデータを取得

準備: インストール

$ pip install awscli
$ pip install chalice boto3

アプリの作成

$ chalice new-project <project-name>
$ nano app.py

app.py

from chalice import Chalice
import boto3
import json

BUCKET_NAME = 'msrks'
s3 = boto3.client('s3')

app = Chalice(app_name='save2s3')
app.debug = True


@app.route('/load/{key}')
def load(key):
    key = str(key)+'.json'
    resp = s3.get_object(Bucket=BUCKET_NAME, Key=key)
    data = json.loads(resp['Body'].read())
    return {'load': data}


@app.route('/save', methods=['POST'], content_types=['application/json'])
def save():
    data = app.current_request.json_body
    if 'key' not in data:
        return {'error': 'please input key'}
    key = str(data['key'])+'.json'
    s3.put_object(Bucket=BUCKET_NAME, Key=key,
                  Body=json.dumps(data))
    return {'save': data['key']}

デプロイ

$ chalice deploy
Regen deployment package.
Updating IAM policy for role: save2s3-dev
Updating lambda function: save2s3-dev
API Gateway rest API already found: m1iu65vuuk
Deploying to API Gateway stage: api
https://m1iu65vuuk.execute-api.ap-northeast-1.amazonaws.com/api/

動作確認

$ echo '{"key" : "lang", "val" : "python"}' | http https://m1iu65vuuk.execute-api.ap-northeast-1.amazonaws.com/api/save/
HTTP/1.1 200 OK
Connection: keep-alive
Content-Length: 16
Content-Type: application/json
Date: Tue, 23 Jan 2018 06:16:02 GMT
Via: 1.1 10885a2c24fad0ff660a4e3a8e3fb801.cloudfront.net (CloudFront)
X-Amz-Cf-Id: ODXxBS7Yq7SNy5RBy3l0N10_awp-z8038s3an0DuMVvyKPbvXwxqXw==
X-Amzn-Trace-Id: sampled=0;root=1-5a66d322-d4765ed44785091e48df33ca
X-Cache: Miss from cloudfront
x-amzn-RequestId: e30e3c23-0004-11e8-88a5-537da6fd5cfc

{
    "save": "lang"
}

$ http https://m1iu65vuuk.execute-api.ap-northeast-1.amazonaws.com/api/load/lang
HTTP/1.1 200 OK
Connection: keep-alive
Content-Length: 42
Content-Type: application/json
Date: Tue, 23 Jan 2018 06:16:40 GMT
Via: 1.1 d653c211343f4b2370c41baf3b65bed6.cloudfront.net (CloudFront)
X-Amz-Cf-Id: FRpHr6jcrOO0-VzC_sZBrhr6G6tntH4OTZADPz9Ey_yeXOiR4v5rqA==
X-Amzn-Trace-Id: sampled=0;root=1-5a66d348-c33cfc4a6f0dc0538d6b2ed3
X-Cache: Miss from cloudfront
x-amzn-RequestId: f9a6b059-0004-11e8-ade1-b3a163f5bf18

{
    "load": {
        "key": "lang",
        "val": "python"
    }
}

参考：ダッシュボード画面