Shantanu's Blog

Corporate Consultant

February 24, 2015

 

python map reduce moedule

Here is how we can use Map Reduce jobs using Amazon EMR

python wordc.py big_file.txt  -r emr --conf=mrjob.conf

The configuration file looks like this...

# cat mrjob.conf

runners:
  emr:
    aws_access_key_id: xxx
    aws_secret_access_key: xxx
    ec2_instance_type: m1.small
    num_ec2_instances: 5

# cat wordc.py
"""The classic MapReduce job: count the frequency of words.
"""
from mrjob.job import MRJob
import re

WORD_RE = re.compile(r"[\w']+")

class MRWordFreqCount(MRJob):

    def mapper(self, _, line):
        for word in WORD_RE.findall(line):
            yield (word.lower(), 1)

    def combiner(self, word, counts):
        yield (word, sum(counts))

    def reducer(self, word, counts):
        yield (word, sum(counts))

if __name__ == '__main__':
     MRWordFreqCount.run()

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February 15, 2015

 

Restrict access to S3 bucket

Let's assume I have a S3 bucket named "mybest". I want to restrict (especially download) access from all IP addresses except 182.72.128.206 that is my work IP address.

I can use this policy to control the access of the bucket from any other IP address other than my office address.

{
    "Statement": [
        {
            "Effect": "Deny",
            "Principal": {
                "AWS": "*"
            },
            "Action": "s3:*",
            "Resource": "arn:aws:s3:::mybest/*",
            "Condition": {
                "NotIpAddress": {
                    "aws:SourceIp": [
                        "182.72.128.206/32"
                    ]
                }
            }
        }
    ]
}

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January 30, 2015

 

Using string templates in python

$to and $from in the docstring can be used as a template so that the values from dictionary can replace the placeholder using substitute method of string.template object. neat !

import string
tmpl = string.Template('''
Hi ${to},
welcome to the club
Regards,
$from
''')
dct={'to': 'Rick', 'from':'Stuart'}

tmpl.substitute(dct)

Labels:


 

lambda functions in python

def lambda_adder(a, b):
    return a+b

This function can also be written as lambda function as shown below:

lambda_adder = lambda a,b: a+b

Call either of the functions above using:
lambda_adder(1,2)

Labels:


January 29, 2015

 

email notification of S3 activity

There is an easy way to get alerts of all your S3 account activity.

1) Go to SNS home page here:
https://console.aws.amazon.com/sns/home?region=us-east-1

2) Create new topic
Topic name can be something like "s3_to_email"

3) Note the Topic ARN:
arn:aws:sns:us-east-1:94331768506:s3_to_email

4) View/Edit Topic policy: Advance view

5) Add the following code after changing the ARN

  {
   "Sid": "zzz",
   "Effect": "Allow",
   "Principal": {
    "AWS": "*"
   },
   "Action": "SNS:Publish",
   "Resource": "arn:aws:sns:us-east-1:94331768516:test",
   "Condition": {
    "ArnLike": {
     "aws:SourceArn": "arn:aws:s3:*:*"
    }
   }
  }

6) Click on "Create Subscription" and subscribe to the topic using email protocol. You will have to check your email and confirm your subscription.

That's it. Now select a bucket in S3 - Choose Events from Properties And add an event pointing to SNS topic that you have just created.

This will start sending you email as and when a file is added to that bucket.
This event needs to be applied to all buckets. A task that can be accomplished by boto.

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