API connection “retry logic with a cooldown period” simulator ( Python exercise )

This is a very simple API call “circuit-breaker” style simulator I’ve written in Python. But since it’s a stateless code snippet, you should call it most likely a “retry logic with a cooldown period” simulator. But there are valid use case scenarios when stateless is the desired state type. For example when a validation of a dataset against a service can either pass or fail and throw an exception and cause the execution flow to halt. This is typical for data-flow styled apps. In such case the circuit-open state is not acceptable. Anyway the goal is to make sure, that whenever we have a connection (or timeout) error during the API call ,we retry after 10 seconds, after 20 seconds, after 30 seconds and then quit trying. The ConnectionError exception is simulated using a non-routable address

However in the microservices world, if you want to implement the full-scale state-full circuit-breaker, please have a look at this article.

import datetime
import time
import logging
import requests

iterator = 1
attempt = 1

# while cycle to simulate connection error using non-routable IP address
while iterator < 40:
        # if iterator inside the range to simulate success
        if 1 < iterator < 8:
            r = requests.get('https://data.police.uk/api/crimes-at-location?date=2017-02&location_id=884227')
        # else iterator outside the range to simulate the error event
            r = requests.get('')
        if r.status_code != requests.codes.ok:
            logging.error('Wrong request status code received, %s', r.status_code)
        r = r.json()
        attempt = 1
    except (requests.exceptions.ConnectionError, requests.exceptions.Timeout,
            requests.exceptions.ConnectTimeout, requests.exceptions.ReadTimeout) as conn_err:
        print(f'bingo, ConnectionError, now lets wait {attempt * 10} seconds before retrying', (datetime.datetime.now()))
        time.sleep(attempt * 10)
        attempt = attempt + 1
        if attempt > 3:
            logging.error('Circuit-breaker forced exit')
            raise conn_err
    iterator = iterator + 1

Also try avoiding Python time.sleep() method in AWS Lambdas as this would not be cost efficient, AWS Step Functions would be much more appropriate.


Tool for migrating data from MSSQL to AWS Redshift part 3 / 3

This tool is now mostly finished. I just need to finish the integration tests for Pytest testing module. Otherwise please feel free to clone, fork or contribute.

You can find it here:



Tool for migrating data from MSSQL to AWS Redshift part 2 / 3

As promised, here’s an update on this project. In the MSSQL part, the T-SQL code is pretty much ready, you can check out the installation script here:


So how is this going to work? The Python wrapper will call the Stored Procedure [MSSQL_to_Redshift].[mngmt].[Extract_Filter_BCP] using PyMSSQL module like this:

EXEC [mngmt].[Extract_Filter_BCP]
@DatabaseName = N'AdventureWorksDW2016',
@SchemaName = N'dbo',
@TargetDirectory = N'C:\mssql_to_redshift\files',
@DryRun = 'False'

You’ll provide the Database name and the schema name, that’s the database you’re connecting to and the schema that’s containing the source tables with the data you are about to transfer into AWS Redshift.

You’ll also provide the target directory on your hard drive, that’s the location where the .csv files will be generated using bcp in the xp_cmdshell wrapper inside the Stored Procedure. This target directory will be created for you inside the Python code in the final version. The last parameter is called DryRun. When set to True, BCP extraction query is modified to return 0 rows for each file using “WHERE 1 = 0” pattern.

Once the Python coding part is ready, these Stored Procedure parameters will be internal and you’ll set these values as arguments while running the Python app.

This SP returns a Python-ready “string tuple” with the generated file names from the current run, in the case it succeeded. This tuple will be used further in the Python code to guarantee we pick up and move over to AWS Redshift only the expected set of files.

The main thing here is, that you need to fill out a table called mngmt.ControlTable. In the Github installation script, I loaded this table with the AdventureWorks DataWarehouse 2016 database columns for the demo purposes. So this table holds values like this:

ControlTable The IsActive flag determines, if the column makes it to the generated .csv file created for the corresponding table. Column_id is defining the order of the columns persisted into the .csv file.

The Stored Procedure [MSSQL_to_Redshift].[mngmt].[Extract_Filter_BCP] is writing the logs to a table called [mngmt].[ExecutionLogs] like this:


And that’s all for now. Have a look at the installation build script, that should be pretty self-explanatory.


Tool for migrating data from MSSQL to AWS Redshift part 1 / 3

Today, I’d like to introduce to you my new project, a SQLServer to AWS Redshift data migration tool . There’s not much tooling for this out there on the Internet, so I hope this tool is going to be valuable for some of you. It’s going to be written in Python 3.7 and once finished, it will be published to my Github account under a MIT Licence. What I’m currently doing is going to be described here in this blog in 2 phases.

Phase #1 will be all about SQL Server coding, there I’ll need to:

  • extract and filter the data from the SQL Server tables I need to transfer to AWS Redshift
  • I’ll need to persist this data using dynamically generated BCP commands into .csv files ( these .csv files will be split based on the target Redshift tables )
  • I’ll need to store these .csv files on a local hard drive.

Untitled Diagram

Phase #2 will be about Python and AWS Boto3 libraries and wrapping this tool all together to push the data through all the way to AWS Redshift. That means:

  • Upload the .csv files from Phase #1 into a AWS S3 bucket
  • Run the copy commands to load these .csv files to AWS Redshift target tables
  • Do the cleanup of the files and write log data

Untitled Diagram2

As soon as I have this initial version out, I would like to extend this tool to be capable of running incremental data loads based on watermarks as well.


A few thoughts on AWS Batch with S3 event-driven usage scenarios

AWS Batch is a great service. This is what AWS says about it: AWS Batch enables developers, scientists, and engineers to easily and efficiently run hundreds of thousands of batch computing jobs on AWS. AWS Batch dynamically provisions the optimal quantity and type of compute resources (e.g., CPU or memory optimized instances) based on the volume and specific resource requirements of the batch jobs submitted. With AWS Batch, there is no need to install and manage batch computing software or server clusters that you use to run your jobs, allowing you to focus on analyzing results and solving problems. AWS Batch plans, schedules, and executes your batch computing workloads across the full range of AWS compute services and features, such as Amazon EC2 and Spot Instances.

What I want to write about in this blogpost is how to make the AWS Batch service work for you in a real-life S3 file arrival event-driven scenario. I use this approach for decoupling the metadata of the file that arrived to spin up a Batch data-processing job where the metadata from the file arrival event define the application logic and the  validations that are processed in the Batch job and when all succeeds, then the Batch job picks up the file itself for processing.

Let’s look at the 2 possible options I ‘ve worked with so far below:


Scenario #1 : A file arrives to a s3 bucket, CloudTrail logs capture the event and raise it to CloudWatch service, and this triggers AWS Batch job as it is a valid CloudWatch target. Use this scenario in case you don’t need to involve heavy logic in the arguments you pass to your Batch job. Typically you would use just basic metadata like the s3 key, s3 “file path” etc.

*Note: Don’t forget to have your CloudTrail log files repository in another bucket then the bucket you use for the file arrival event, otherwise the CloudTrail log files can easily keep triggering the Batch job 🙂

Scenario #2: A file arrives to a s3 bucket, Lambda function has this event set as an input, and this Lambda function triggers a AWS Batch job using the standard BOTO3 API library. Use this scenario when you need more logic before triggering the Batch job. Typically you might want to split the s3 file “file path”, or use the file size etc. and add some additional conditional logic for the arguments you provide to the Batch job.

Both of these solutions have some serious downside though. Solution #1 is weak in the way, that you are not able to add more complex conditional logic for the Batch job arguments. Solution #2 is weak in the way, that AWS Lambda Function has a 15 minute timeout , but the Batch job can run much longer, and therefore you never hear back from the Batch job execution in the context of the Lambda Function. So you’d have to have another Lambda function acting as a Batch job status poller. Ofcourse, you can follow up watching over the Batch job in CloudWatch logs or in the AWS Batch Dashboard, but in this case, you might want to try out the AWS Step functions. They allow you to add orchestration to your Lambda functions firing the Batch jobs. You can see more about AWS Step functions running Lambdas firing Batch jobs here .

Dummy .csv or flat .txt file generator in Python 3.7

I just finished my dummy csv or flat text file generator written in Python 3.7.

In my opinion, such project is quite unique. I use this tool for large files generation, so I can do performance testing loads in ETL data-ingestion pipelines without loading production data in Dev / Test environments or without the need to de-identify PII.

Feel free to clone, fork or contribute with new features and feedback.

The project is located here:



In the future,I’d like to make it also AWS Server-less design event driven project, so stay tuned 🙂

Spinning up a Docker container with Flask and Python

Imagine you need to replicate an existing web API returning a JSON ( listing all feeds in some system ) on your local machine for further development purposes and possible extensions. Today I’ll demonstrate how to achieve this using Docker container , Python and Flask. Note that this tutorial requires some previous experience with Python and Docker. Have a look at Flask, it’s a powerful and easy to use Python web framework.

The source web API we’ll be replicating is returning a valid JSON structure listing all the feeds:

  "feed_name": "feed1",
  "feed_type": "feed type 1",
  "filemasks": [
  "feed_name": "feed2",
  "feed_type": "feed type 2",
  "filemasks": [

Let’s save this dummy JSON file as feeds.json on our local file system.

Next we’ll setup the environment and start with Docker:

mkdir docker-api

mkdir docker-api/app

mkdir docker-api/feeds

cd docker-api

#1) create Dockerfile:

FROM python:3.6-stretch

COPY . .

RUN pip install -r requirements.txt


ENTRYPOINT ["python3"]

CMD ["app.py"]

#2) create requirements.txt:


#3) download the feeds.json file from the website
to your local filesystem into docker-api/feeds/


Let’s move forward with the Python application, which is reading from the Docker image

the feeds.json file and exposing this JSON to the Flask web API. We won’t be stepping into

any actions like GET or PUT, just returning the complete JSON file listing all the feeds.


I prepared the Python app in the location docker-api/app/app.py and it is looking like this:

import os
from flask import Flask
from flask import Response

app = Flask(__name__)

def returner():
    path = os.path.abspath(os.curdir) + '/feeds/feeds.json'

    with open(path,"r") as f:
        data = f.read()
        resp = Response(response=data,

if __name__ == '__main__':
    app.run(debug=True, host='')

The next step is spinning up the docker container ( once we build the image of course )

cd docker-api/ 

docker build -t feeds . 

docker run -d -p 5000:5000 feeds 

docker container list 

*optionally docker container kill(or stop) container_id 
incase you need to "restart" the container
Btw. docker kill vs docker stop is an interesting topic and is discussed for example here
Let’s confirm that your Python project structure is looking like this:

and voila, after running docker run -d -p 5000:5000 feeds , if you lookup the webpage


in your web browser, you should be getting the response with the desired JSON listing all the feeds.

You might want to check-out also curl.

Fibonacci sequence ( Python exercise )

Let’s continue with the simple Python exercises I’ve been messing around lately. This is a classical question at Dev job interviews, the Fibonacci sequence code. The idea behind this is to come up with code, that sums up the previous 2 member values for a member in the sequence, simply expressed like 1,2,3,5,8,13…

Below are my personal takes on this problem.

1: The nice and performing solution

#get fibonacci
import sys

def main(arg):
    seq_len = arg
    seq_len_iterator = 2
    var1 = 1
    var2 = 2
    fibonacci = ([var1, var2])

    while seq_len_iterator < seq_len:

        var3 = var1 + var2

        i = len(fibonacci)
        var1 = fibonacci[i-2]
        var2 = fibonacci[i-1]

        seq_len_iterator = seq_len_iterator + 1

    print(f'Fibonacci sequence for {seq_len} sequence members goes like: {fibonacci}')

if __name__ == '__main__':
        arg = int(sys.argv[1])
        print(f'Invalid input, must be integer!')

Execute with the needed sequence member count argument like for instance :

python.exe C:/codility/fibonacci/__main__.py 10


2: The alternative “nested-iterations” solution ( Not performing over ~30 sequence members count, durations exponentially grow, however its another example of a valid solution and can be useful if you need to warm oneself during long winter cold nights somewhere outside 🙂 )

#get fibonacci
import sys

def main(arg):
    seq_len = arg
    seq_len_iterator = 2
    iterator = 1
    var1 = 1
    var2 = 2
    fibonacci = ([var1, var2])

    while seq_len_iterator < seq_len:
        if iterator == var1 + var2:
            var1 = var2
            var2 = iterator
            iterator = iterator + 1
            seq_len_iterator = seq_len_iterator + 1
            #print(f'Fibonacci member found in try #: {iterator}')
            iterator = iterator + 1

    print(f'Fibonacci sequence for {seq_len} sequence members goes like: {fibonacci}')

if __name__ == '__main__':
        arg = int(sys.argv[1])
        print(f'Invalid input, must be integer!')

Execute with the needed sequence member count argument like for instance :

python.exe C:/codility/fibonacci/__main__.py 10

Binary gap length ( Python exercise )

Sometimes I like to mess around http://www.codility.com , doing the excercises trying to keeping my development skills fresh. This is my take on the binary gap length problem using basic Python 3. The binary gap length is an excercise where you need to come up with a code, returning the longest sequence of zeros in a 16 digit “binary” string. This question also often shows up at developer job interviews.

#get max binary zeros gap
import re
import sys

def get_binary_gap(input_seq):
    iterator = 0
    iterator_zeros = '0'

    while iterator < 16:
        if iterator_zeros in input_seq:
            stack = len(iterator_zeros)
            if stack > iterator:
                output = stack

        elif iterator_zeros not in input_seq and len(iterator_zeros) == 1:
            output = 0


        iterator_zeros = iterator_zeros + '0'
        iterator = iterator + 1
    return output

def main(arg):
    input_seq = arg

    if len(input_seq) == 16 and bool(re.match("^[0-1]{1,16}$", input_seq)):
        output = get_binary_gap(input_seq)
        print(f'The max binary gap of zeros in sequence {input_seq} is {output}')

        print(f'invalid input sequence {input_seq}')

if __name__ == '__main__':
    arg = str(sys.argv[1])

Execute with the binary sequence argument like for instance :

python.exe C:/codility/binary_gap/__main__.py 0100000101010100