Pythonic Moments

I’ve been heads-down with development work for months it seems, a lot of it in Python, and found a couple of great resources recently that I wanted to share.

If you code in Python and haven’t already heard of Dan Bader or his book, “Python Tricks: A Buffet of Awesome Python Features“, check both of them out. Dan has a series of helpful YouTube videos as well, some of which cover Python Tricks material.

If you listen to podcasts, check out Michael Kennedy‘s “Talk Python To Me” series. He also does a more concise, headline-oriented podcast called “Python Bytes

Huzzah, I’m AWS Certified!

I passed the AWS Certified Solutions Architect – Associate exam on 12/11 and the AWS Certified Developer – Associate exam on 12/15. Woohoo!


AWS re:Invent 2017 Download

I had a good time at AWS re:Invent 2017 last week, despite being sick as a dog for most of it. Though I caught fewer sessions than I would have liked, the ones I did attend on serverless topics were top notch. Here are some links to my favorites:

ARC401 – Serverless Architectural Patterns and Best Practices


  • Serverless foundations
  • Web applications
  • Data Lakes
  • Stream processing
  • Operations automation (e.g., Tailor, for automating AWS account creation)
  • Excellent review of best practices and new features in Lambda

SRV401 – Become a Serverless Black Belt: Optimizing Your Serverless Applications


  • Optimization Katas
    • Lean Functions
    • Eventful Invocations
    • Coordinated Calls
    • Serviceful Operations
  • Cold start issues in Lambda
  • Instrumenting Lambda with XRay
  • Resource allocation
  • Concurrency vs. latency
  • Compelling customer story from ACloudGuru’s VP of Engineering on going 100% serverless

SRV305 – What’s New in Serverless


  • Announced Serverless Application Repository
  • Reviewed new Lambda console
  • Reviewed new Lambda features
  • Reviewed Cloud9 IDE
  • Reviewed XRay tracing for Lambda
  • New API Gateway features
  • Compelling customer story from FICO’s VP of Engineering

Integration Gotcha: SNS and Lambda

When using SNS pub/sub components, a common integration pattern is to use Lambda to process SNS messages. This can include the use of data blobs as the SNS payload for doing file processing, data transformations, and archiving data in S3 among other things. SNS messages have a large payload limit of 256KB per message, but I recently ran into a situation where I could not reliably deliver messages that were sized well under that limit.

As it turns out, when Lambda is consuming your SNS large payloads in events, you hit a limit within Lambda that is exactly half of the SNS payload limit. For Event (asynchronous) invocations in Lambda, there is a 128KB payload limit. So, if your SNS messages are not being processed by Lambda, check the size of the messages and verify that they are below 128KB. This was a confusing problem until I looked at the CloudWatch console for SNS message deliveries and noticed the errors there.



Patterns for Kinesis Streams

I’ve recently been working on a streaming component in a project and have been spending a lot of time with both Kinesis Streams and Kinesis Firehose. I tend to think of the two as event queue frameworks, with Firehose also having the ability to forward events to other AWS services like ElasticSearch (for Kibana-style dashboarding) and backup the same data to a S3 bucket. If you don’t need either of those destinations, then most likely you will get plenty of mileage out of working with Streams alone.

Potential uses abound, but one powerful pattern is making Kinesis a destination for CloudWatch Logs streams via subscription filters. By creating a Kinesis stream and making it a CloudWatch log destination in one account, you can readily add CloudWatch subscription filters in other accounts to create a cross-account log sink. Once your CloudWatch Logs are in one or more Kinesis Streams shards, you can process that log data via Lambda and/or possibly forward to Kinesis Firehose for ES/S3 delivery. There’s a great blog post over at Blend about this exact sort of usage, including a link to their GitHub repo for the CloudFormation templates they use to build and deploy the solution.

One of the best overviews I’ve read recently about design and scale-out issues around event queue processing and how Kinesis resolves, by design, a lot of the challenges therein (e.g., data duplication, ABA problems) is by the fine folks over at Instrumental, entitled “Amazon Kinesis: the best event queue you’re not using“. If you are considering using Kinesis at scale, or are already designing/deploying a consumer/producer pattern to be used with Kinesis, I highly recommend you check out the Instrumental blog post.


Python’s logging() module in a boto3/botocore context

Python’s logging module provides a powerful framework for adding log statements to code vs. what might be done via using print() statements. It provides a system of logging levels similar to syslog-style levels that can be used to produce both on-screen runtime diagnostics as well as more detailed logs with full debug level insights into per module/submodule behavior.

Managing usage of logging() can be complicated, especially around the hierarchical nature of the log streams that it provides. I have developed a simple boto3 script that integrates logging to illustrate a basic usage that is easy to adopt and, in the end, not much more work than using print() statements. For detailed information on logging beyond what I present here, consult the excellent Python docs on the topic, as well as the links in the References section at the end of this post.

Logging Configuration

The setup for logging() that I am using involves two configuration files, logger_config.yaml and logger_config_debug.yaml. The difference between the two files has to do with the log levels used by the log handlers. By default, the example module uses the logger_config setup. This config will produce no screen output by default except at the ERROR level and above. It produces a log file, however, that contains messages at the INFO level for the module and at the WARNING level for boto-specific calls.

Note: boto (including botocore) ships with some logging() active at the INFO level. While not as detailed as DEBUG, there’s enough busyness to that level of logging by boto that you will likely want to not see its messages except when troubleshooting or debugging your code. This is the approach I took with the current configuration, by opting to set custom logger definitions for boto and friends, so that the root logger will not by default display boto’s native log level messages.

Let’s take a look at the default logging configuration file I’ve put together, logger_config.yaml:

version: 1
disable_existing_loggers: False
    format: "%(asctime)s %(levelname)s %(module)s %(message)s"
    format: "%(asctime)s|%(levelname)s|%(module)s.%(funcName)s:%(lineno)-2s|%(message)s"
    format: "%(asctime)s|%(levelname)s|%(pathname)s:%(funcName)s:%(lineno)-2s|%(message)s"

    class: logging.StreamHandler
    level: DEBUG
    formatter: simple
    stream: ext://sys.stdout

    class: logging.StreamHandler
    level: ERROR
    formatter: fancy
    stream: ext://sys.stdout

    class: logging.handlers.RotatingFileHandler
    level: DEBUG
    formatter: debug
    filename: "/tmp/deployVpc.log"
    maxBytes: 1000000
    backupCount: 10
    encoding: utf8

    level: WARNING
    handlers: [logfile, screen]
    propagate: no
    level: WARNING
    handlers: [logfile, screen]
    propagate: no
    level: WARNING
    handlers: [logfile, screen]
    propagate: no
    level: INFO
    handlers: [logfile, screen]
    propagate: no
    level: INFO
    handlers: [logfile, screen]
    propagate: no

  level: NOTSET
  handlers: [console, logfile]

I chose to use YAML for the configuration file as it’s easier to parse, both visually and programmatically. By default, Python uses an INI file format for configuration, but both JSON and YAML are easily supported.

At the top of the file is some basic configuration information. Note the disable_existing_loggers setting. This allows us to avoid timing problems with module-level invocation of loggers. When logging per module/submodule, as those modules are imported early in your main script, they will not find the correct configuration information as it’s yet to be loaded. By setting disable_existing_loggers to False, we avoid that problem.

The remaining file consists of four sections:

  • formatters
  • handlers
  • loggers
  • root logger definition


Formatters are used to define the log message string format. Here, I am using three different formatters:

  • simple – very simple and brief
  • fancy – more detail including timestamp for a helpful log entry
  • debug – fancy with module pathname instead of module name, useful for boto messages

By default, I leave simple for the console handler (for root logger), use fancy for the screen handler, and debug for the logfile handler.


Handlers are used to define at what level, in what format, and exactly where a particular log message should be generated. I’ve left console in its default configuration, but added a StreamHandler and a RotatingFileHandler. Python’s logging module supports multiple types of handlers including Syslog, SMTP, HTTP, and others. Very flexible and powerful!

  • console – used by the root logger
  • screen – log ERROR level and above using fancy formatting to the screen/stdout
  • logfile – log DEBUG level messages and above using debug formatting to a file in /tmp that gets automatically rotated at 1MB and retention of 10 copies


Loggers are referenced in your code whenever a message is generated. The configuration for a given logger is found in this section of the configuration file. In my case, I wanted a separate logger per module/function if necessary, so I’ve made entries at that level. I also include entries for boto and friends so I can adjust their default log levels so I don’t see their detailed information except when and where I want to (i.e., by logging at WARNING instead of INFO or DEBUG for normal operation). A logger entry also defines where log streams should end up. In this case, I send all streams to both my screen handler and my logfile handler.

I also don’t want custom loggers to propagate messages throughout the logging hierarchy (i.e., up to the root logger). So I’ve set propagate to “no”.

Implementing logging in code


I created a module called which is where I do the initialization for defining how logging() will be configured, via the configuration files:

#!/usr/bin/env python
"""Setup logging module for use"""

import os
import logging
import logging.config
import yaml

home = os.path.expanduser('~')
logger_config = home + "/git-repos/rcrelia/aws-mojo/boto3/loggerExample/logger_config.yaml"
logger_debug_config = home + "/git-repos/rcrelia/aws-mojo/boto3/loggerExample/logger_config_debug.yaml"

def configure(default_path=logger_config, default_level=logging.DEBUG, env_key='LOG_CFG'):
    """Setup logging configuration"""
    path = default_path
    value = os.getenv(env_key, None)
    if value:
        path = value
    if os.path.exists(path):
        with open(path, 'rt') as f:
            config = yaml.safe_load(

def configure_debug(default_path=logger_debug_config, default_level=logging.DEBUG, env_key='LOG_CFG'):
    """Setup logging configuration for debugging"""
    path = default_path
    value = os.getenv(env_key, None)
    if value:
        path = value
    if os.path.exists(path):
        with open(path, 'rt') as f:
            config = yaml.safe_load(

This module defines two functions: configure() and configure_debug(). This provides another way of running a non-default logging configuration without using the LOG_CFG environment variable (i.e., on a per-module basis). When you setup logging in your module like so:

logger = logging.getLogger(__name__)

You would simply edit the first line to use .configure_debug() instead of .configure().


Usage is straightforward, simply do the following in each module you wish to use logging(). Refer to the script for the full syntax and usage around these bits of code.

Note: requires use of AWS API key access that is stored in a config profile (I used one called ‘aws-mojo’, change to your own favorite profile). It will create a VPC and Internet Gateway in your AWS account. But it will also, by default, remove those objects as well. Caveat emptor…

  1. Import the logging modules and loggerSetup module
import logging, logging.config, loggerSetup
  1. Activate the logging configuration and define your logger for the module
logger = logging.getLogger(__name__)

Note: By using __name__ instead of a custom logger name, you can easily re-use this setup code in any module.

  1. Add a logger command to your code using the level of your choice:'EC2 Session object created')

That’s all there is to it. Below are some screenshots that show the handler output (screen and logfile) for both the default and debug configurations. Hopefully this will encourage you to look at using Python’s logging() framework for your own projects.

The full source for all of the logging module configuration as well as sample boto script is available over on GitHub in my aws-mojo repository.


Example: Default configuration – output to screen handler (should be no output except ERROR and above)

Default screen handler output

Example: Default configuration – output to logfile handler (should be messages at INFO and above for your code and at WARNING and above for boto library code messaging)

Default logfile handler output

Example: Debug configuration – output to screen handler (should be messages at INFO and above for your code and at WARNING)

Debug screen handler output

Example: Debug configuration – output to logfile handler (should be messages at DEBUG and all levels for your code and boto library code messaging)

Debug logfile handler output


Continue reading

Followup: Visual Studio Code

So, it’s been almost a couple of weeks now of hardcore Visual Studio Code (VSC) usage on my part. I have to say, it’s fantastic. Not a single crash after a solid two weeks of varied development (CloudFormation, Python, shell, and HCL (Terraform)) and at some points, intense Git activity with different repositories and different SCM endpoints. It’s easily 30% more performant than my Atom environment ever was.

The rock solid Git integration is the one feature I appreciate the most. It really works well with everything I do on a regular basis. I did install the GitEasy package just to see if it added anything beyond the built-in support. So far, I only use one GitEasy command reliably, and that’s GitEasy:PushCurrentBranchToOrigin.

I’ve also been able to increase my normal productivity after I installed a marketplace extension called “macros“. I use macros to automate combinations of git commands I often chain together manually (as well as any other keybindings I see fit to construct).

Nice job, Microsoft. I think that’s the first time I’ve said those words after nearly 30 years in technology.