Javier Rengel

Senior Full-stack Engineer

About me

I'm a senior software engineer with over 12 years of experience. I specialize in backend web development, but I have experience and a good understanding of the full stack, from frontend to devops. I'm most productive at present with the Scala, JS and Python ecosystems, however I consider myself to be technology-agnostic, and can quickly adapt to any technology.

Most of my professional experience has been with startups in London. I enjoy the thrill of building something brand new, plus the fast paced environment and good vives with a small and dedicated team.

I'm currently available for hire as a permanent or contractor on a fully-remote basis.

During my spare time I am also constantly learning new technologies and building pet projects of very different natures: from web apps to videogames to mobile apps to electronics. I share them in my blog, Coconauts.net.

Favourite technologies: Python, JS, Scala, Go, React, AWS, GCP, Docker, Kubernetes, Datadog, Redis, PostgreSQL


This is a list of my previous companies, and some technologies and stuff I've done there

Pashi is an OS for factories. With a simple No-code editor you can view and edit the different hardware devices of a production line.


I joined Pashi as a technical leader. I was in charge of maintaining, updating, bugfixing the main codebase, while I was building a brand new interface and backend for extending the compatibility of the product with multiple production line types, using no-code principles.


  • Technologies: Go, VanillaJS, Docker, Postgres, Cypress.
  • On my first day, I dockerized all the different Go services for everyone to run it locally.
  • I introduced tests and CI.
  • I built a no-code report engine to visualize the status of the production line in realtime.
  • As the worker with more seniority, I introduced good startup practices, to improve our efficiency as a team.
  • I was continuously doing tech talks even for non technical coworkers, and writting documentation of all different components of the product.
Stacker aims to build a revolutionary service following no-code principles that will allow non technical users to build their own portals by just importing their data from Airtable or Google sheets.


I joined Stacker as a full stack engineer at a very early stage, so we experienced some iterations in the product. It was a very challenging and exciting product to work on, since the goal to allow non technical users to build their own apps was not an easy task; nor from the product point of view (no one has cracked the magic formula yet) or from a technical point of view. We had to design a very dynamic API that could not be tied to a specific schema or configuration, with several generic layers (like permissions or roles), as well as a data cache to keep it performant.


  • Technologies: Google cloud, Kubernetes, React, Python Django, Celery, Postgres, Memcached, Cypress.
  • I was in charge of devops and architecture: deployed services using Kubernetes in GCP.
  • Advance service monitoring on Datadog.
Lantum hired me as a contractor to design, maintain their python microservice architecture on Kubernetes in AWS. Eventually I started also making changes to the frontend code built in Angular.


  • Technologies: AWS, Angular, Python, Kubernetes
  • I was in charge of devops: I designed and maintained Kubernetes staging and prod clusters in AWS
Network Locum is a market network that unifies Practices and Locums (GPs) on a single platform, managing sessions and rotas for the practices, and allowing the Locums to easily apply for jobs. Processing and emitting invoices for both in the process.


Smart team of people with different approaches to work. We all worked really hard on doing a codebase refactor in 6 weeks, defining and creating from scratch all the existing platform features in new Django, Flask docker microservices. We then shifted to a squads-based structure, and I joined the one in charge of the billing process.


  • Full microservices architecture using Docker and Rancher
  • Backend mostly built in Python3, Django and Flask (and a bit of Scala) with PostgreSQL and Redis for persistence
  • TDD and BDD
  • Continuous integration using Jenkins and Travis
  • Conducted software developer interviews
Top10 was a hotel metasearch startup company based in London, taking advantage of brand new web technologies and good marketing campaigns.


It was a small startup with a team of top-talent engineers, I had the chance to vastly improve my knowledge both in new technologies and good code practices.


  • Backend microservices development in Scala
  • Full custom CMS app built in Scala (Play Framework)
  • CI with Jenkins
  • Polyglot persistence with Cassandra, Memcached, ElasticSearch, Redis
  • Heavy use of Amazon WS (DynamoDB, EC2, S3, SQS, SNS, etc)
Openbet are the world's leading provider of interactive gaming and betting solutions, providing software solutions to William Hill, Ladbrokes, Betfair, etc.


While the codebase and project was not very flashy, I learned how it feels working in a large company with a large team and I also was introduced to agile (standups, code reviews)


  • Web backend development for sportsbook sites in Tcl
  • Troubleshooting, QA, optimization and code analysis for existing products
  • Automation scripts in Bash and Expect in Jenkins.
  • Release manager: in charge or the team's code merging, code deployment, and direct support towards clients
Asesores locales is a well renowned medium-size consultancy company based in Madrid, Malaga and Cadiz (Spain). It's main line of business is the development of software for local goverments, as well as training in several fields. Other clients include companies both spanish and international.


Asesores Locales was my first job as a developer. I started by learning some basics on JEE and web development, but fueled by my motivation, after the cuourse of my time there I ended up leading development of some projects, bringing new technology, and mentoring others (I was the official "innovator geek mind" in the company).


  • JEE development in several projects, as part of teams and autonomously
  • GIS system development in JEE using MapServer for custom street location service
  • Devops: Installation, configuration and maintenance of IBM servers with Windows Server 2008 R2, CentOS and VMWare VSphere hypervisor 5.0.
  • Administration of Oracle, MySQL and PostgreSQL databases
  • Product presentations (inside and outside the company)
  • Manager role in some projects

Code showcase

If you are interested on how I code, here there are a few easy-to-review projects showcasing different technologies, that you can check on Github.

Scala Akka-HTTP

Scala REST API to manage Tasks with Akka-HTTP and Slick 3 to be used as a template

Django Rest

Python Django REST API to manage Tasks to be used as a template

Perfect Stack

Ideal docker microservice Infrastructure with multiple languages (Python + NodeJS), databases and unit, integration and behaviour tests


NodeJS + Express + Elasticsearch showcase app to search Pokemons

On my Github accounts (personal and Coconauts ) you can find tons of other projects on languages like NodeJS, Golang, C++, C# or Kotlin.


Javier has been our most productive developer over the past year. Notably, Javier has been reliably productive in both high and low morale environments. He's a great, friction-less team member - he always has cool side projects to share. Javier has a systematic approach, and he delivers consistent, well-tested code. He always has a great local dev environment setup, and combined with fast iterations on unit and integration tests, makes you feel very productive pair-programming with Javier.

Douglas Hindson Lead Backend Developer at Lantum

Javier has been with the company for over two and half years, and is a committed and talented developer with strong experience in Scala (inc. Akka, Play), Java, and the AWS platform. Aside from his technical skills, Javier is an absolutely brilliant guy to have in the team with a positive, can-do attitude, a great sense of humour and unbridled enthusiasm for technology. In his spare time he develops indie computer games and is building a smartwatch.

Tom Leathes Top10 CEO

Javier and I worked together in NetworkLocum. We were backend colleagues. He’s a top-notch engineer, and a model I tried to follow while working with him. He had more experience than me in the environment and in the company, he has been always supportive and willing to help, not only me but everyone around. His standards of quality are quite high, and he is always trying to improve the test environments and promoting best practices.

Marga Rodríguez Software engineer at Network Locum

Javier has proven himself to be a valuable asset ot both the team and the company. He is a skilled developer and works well, both with his team mates and the customer, to get projects completed on time to a high standard. Javier often takes the initiative to develop new scripts and software to help out the team and can be trusted to work autonomously on tasks.

Robert Hayward Technical Lead at Openbet


Some personal projects

Some pet projects that I feel particularly proud of

Watchduino 2

WatchDuino 2 is a SmartWatch built in Arduino that uses Bluetooth for sending messages to Android, finalist on the Hackaday Prize 2015.


A web emulator of NES games with Achievements and multiplayer gameplay via websockets, featured on Hackernews.

StarCraft Unity3D

RTS template optimized for mobile, built in Unity3D inspired in StarCraft


Lightweight online music player, powered by NodeJS, Sqlite and JPlayer with tons of features

You can find the full list of projects at Coconauts projects/


My CV is available in different and unusual formats, check it by yourself:

The original file is written in markdown, all other files are generated using that markdown file (even json). For HTML and ODT I use pandoc, for json I built my own markdown parser using a nodejs script. You can read more about this in my Github repo

Follow up

I keep a blog on Coconauts.net , where you can follow all my developments. You can also find me on social networks:

Alternatively, If you'd like to contact me, you can send me an email Or book a call with me on Calendly.