Lambdaのお勉強がてらに。
s3バケットにアップロードされたgzファイルを展開して、CloudWatchLogsに出力する。

analyze_s3logs
from __future__ import print_function

import json
import urllib
import boto3

import gzip

print('Loading function')

s3 = boto3.client('s3')

def lambda_handler(event, context):
    print("[LambdaLog] Received event: " + json.dumps(event, indent=2))

    # Get the object from the event and show its content type
    bucket = event['Records'][0]['s3']['bucket']['name']
    key = urllib.unquote_plus(event['Records'][0]['s3']['object']['key']).decode('utf8')
    try:
        s3.download_file(bucket, key, '/tmp/file.gz')

        f = gzip.open('/tmp/file.gz', 'rb')
        content = f.read()
        f.close
        print(content)

        return 0
    except Exception as e:
        print(e)
        print('[LambdaLog] Error getting object {} from bucket {}. Make sure they exist and your bucket is in the same region as this function.'.format(key, bucket))
        raise e

元記事はこちら

s3に圧縮ファイルがアップされた際に、解凍して要素をCloudWatchLogsに出力するLambda Function(python版)