When you configure an AWS Lambda, you can configure it to only allow a certain number of concurrent executions through the “Reserve concurrency” setting. For example, it is possible to configure a Lambda to only allow a single concurrent execution.

Even though AWS provides lots of documentation on the topic, there was just too much of it (or I was just too lazy to read it all) and I was not able to fully understand what was the behavior when no more concurrent executions were available. I therefore went ahead and tried it out.

Creating a test lambda

First I created a test lambda…


GitHub contributors statistics are often helpful to get the pulse of a GitHub repository. They make it possible to have a break down of added/removed lines of code and number of commits by contributors. Quite handy!

But when you are trying to get a higher level view and get the pulse of your entire GitHub organization, it becomes more complicated:

  • There’s no easy way to export the data.
  • You have to go in multiple repositories.

In my case, I work for a company that has more than 150 repositories. …


It is common practices to define cloud infrastructure using an Infrastructure as Code (IaC) tool like Terraform, CloudFormation or the Serverless Framework. All these tools have something in common: they require you to define your infrastructure in YAML format. In my opinion, these YAMLs formats look nice at the beginning but, in the end, they result in many problems and limitations.

Luckily for us, there’s been a new kind of kid around the IaC block to fix these problems. These new tools allow you to define your infrastructure using normal code (Python, JavaScript, TypeScript, Java, C#) instead of YAML. The…


AWS lambda functions are the foundation of serverless computing on AWS. They are useful to react to AWS events (SNS message published, file uploaded on S3, etc) but are also often used to just do some serverless computing. You invoke your lambda with some input, it computes something and returns the result. To be more precise, you invoke your lambda function with a JSON object and it will return another JSON object.

This article will first show you some of the limitations (or surprising behaviors) of the default .net AWS Lambda JSON serializer. …


When building a web application using a serverless micro-service architecture on AWS, you end up using lambdas extensively. Lambdas are very useful and simple but they suffer from the cold start problem. As described in details by Serhat Can in this article, a cold start is defined as:

A latency experienced when you trigger a function.

A cold start only happens if there is no idle container available waiting to run the code. This is all invisible to the user and AWS has full control over when to kill containers.

So when a user of a serverless web application is…

Maxime Beaudry

Back end developer at LANDR Music

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