Tips and lesson learned about AWS Lambda and Dynamo DB in last year

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Serverless is a revolution for interpreted, single threaded languages such as Node.js or Python. JavaScript engineers have got possibility to write scalable and fast architecture without going too deep into multi threaded issues. Initialisation of Node.js and Python processes is fast, which makes them ideal choice to use for AWS Lambda. Functions can be run in many instances in parallel with autoscaling (based on real traffic). You can control that and eg. prevent spinning up too many instances (reserved concurrency) or set min. instances available to prevent cold starts (provisioned concurrency). One part of your application can be run eg…

Engineers spend a lot of time debugging and looking for performances bottlenecks. Memory leaks, split brains issues… You need to know, how to write good code but also predict which parts of service will need more power and eventually move them into separate microservice or create serverless function (eg. AWS Lambda).

PDF renderer engine is good case for using AWS Lambda, because it uses a lot of memory in comparison to the rest of my application. I want to share with you implementation of PDF news app which I have created based on AWS: EC2, S3, DynamoDB, Lambda.


Application renders news in PDF for chosen country and category. As a source of news I use REST endpoint. UI is simple React app and server is created by Express.js. Source code:


React with Redux is probably the most popular front-end framework in this year. Redux is great and has changed architecture of front-end apps. If you are looking for new job, you probably will find some interesting offers with Angular 1.x, Angular 2 and others, but most interesting are about React & Redux.

The choice for a lot of programmers is quite obvious, but we should consider some cons of using Redux:

  1. It’s not easy to switch to work with reducers
  2. Don’t Repeat Yourself
  3. Care about performance — render()

It’s not easy to switch to work with reducers

You will need to care about functional principles and always return new value based on previous state. Sometimes it’s easy (simple string, objects or array operations) as:

return {…previousObject, newValue: value}

but for more complex changes you probably would like to use Immutable.js or similar library.

During the work on large application you will need to think about combine reducers, higher-order reducers, separate UI…

I like using ESLint and JSCS with Airbnb preset, so code needs to be strict. Sometimes this is painful, but I definitely agree, that this kind of work keeps code more cleaner and helps cooperate with programmers, which very often have different coding styles.

If you don’t use ESLint, lets try and install also Airbnb package:

Event handlers in React

If you work on component in React you probably need to create some custom events, callback functions. Popular convention in React is to name handler method similar as

handleChange() {...}

when your component looks similar as

render() {
return(<MyInput onChange={...} />)


What I really like in Sass and in similar CSS preprocessors is possibility to keep common reusable classes in one place and after extend or include them. The goal of this post is to show you, how easy is to create fancy background zoom effect on hover state.

Class which cares hover-scaling effect

As you see in code above zoom effect is done by CSS3 transform and transition properties. …

Miron Machnicki

Full-stack developer - react.js, node.js, serverless. @machnicki

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