My Adventure to Nantes for Europe's Largest DevFest

DevFest is a community-led tech conference series hosted by Google Developer Groups (GDGs) that happens around the world. Each event is organized by local GDGs and features a mix of talks, workshops, and networking opportunities for developers of all skill levels.

I discovered them while trying to find events where I could submit my talk proposals. Once you have a talk you put a lot of work into and that people appreciate, you really want to share it with a wider audience.

So after Devoxx 2025, I submitted my two talks, La réactivité et les signaux: démystifions la magie du frontend and En JavaScript, il y a un paquet pour tout... et souvent pour rien., to many meetups and conferences. On June 24, I received an email from Conference Hall, a platform hosting CFPs, telling me that one of my talks had been accepted for DevFest Nantes 2025. I was so happy to explore a new conference!

DevFest Nantes 2025 ​

Life is currently driving me more than I'm driving my life. I barely read any of the emails from the organizers. I had no idea what to expect.

DevFest Nantes is the largest DevFest in Europe: more than 3,500 attendees, 2 days, 4 tracks, 71 talks and 90 speakers. That's huge!

The conference started with the speakers' dinner on Wednesday, October 15. This took place in the Carrousel of the Marine Worlds where we had the privilege of visiting it and taking a ride.

Then we had a networking event to meet and connect with other speakers. It's always a pleasure to see familiar faces and discover new speakers. This is even more true when the food is good. Your social battery has to be full before going to a speakers' dinner!

The event started on Thursday, October 16, 2025. It took place in the Nantes Congress Center. The building is really impressive, with very large rooms. One thing really impressed me: each sponsor's stand was beautifully decorated, on theme, creating a magical atmosphere that was very pleasant. Even the activities to win goodies and attract people were created just for the event. The food was amazing, with plenty to eat and no waiting time. There was even a quiet room for speakers to relax.

While waiting for a talk to start, I was scrolling on LinkedIn and I saw a post by Xavier saying that he was at DevFest Nantes. Maybe you don't know him. He has a YouTube channel named xavki where you can learn everything about cloud and infrastructure. It's a gold mine! A friend of mine got the job he has today thanks to him. So, I went to say hi to him.

Honestly, I was lost for words for a couple of seconds. I was like a child in front of their favorite hero. While we were talking, Stéphane joined us. Unexpected! Stéphane has a blog named DevSecOps containing so much valuable information. Mind-blowing moment.

DevFest Nantes is also a party between the first and second day. You can meet people, a lot of people, eat good food, dance, and simply enjoy the moment. You won't have any photos because what happens at DevFest Nantes stays at DevFest Nantes. With a glass of wine in my left hand and a crêpe in my right hand, it's hard to take pictures.

The last scheduled slot on Friday was a show from La Faltazi. Forty-five minutes of pure laughter. What a great idea to end the conference with improvisational theater! An amazing performance and a perfect ending.

This was the conference in a few words but what about the talks?

There are things that won't change. Until the last minute, I hadn't read the program, so I mostly followed my intuition when choosing which events to attend. For example, I'm writing a talk about AI so I attended some of the talks related to this topic, to see how they approached it, and to try to bring something new. I was not really interested in the content.

The talks I attended:

• Thursday, October 16, 2025
  • Advice Well Taken by Dasha Ilina
  • Ressusciter vos présentations en articles de blog avec AWS Amplify Gen 2 et Amazon Bedrock by Adrien Lebret
  • Révolution TanStack Query : Enfin une bonne gestion d’état by Lucas Audart and Mickael Alves
  • The future of routing with the Navigation API by Eduardo San Martin Morote
  • From RAG to riches : les secrets des LLM augmentés par la donnée ! by Laurent Mangin
  • État des Lieux de la Souveraineté du Cloud : Des Clouds Publics aux Clouds Confidentiels by Seifeddin Mansri
• Friday, October 17, 2025
  • Karpenter * Keda : Le duo gagnant du FinOps by Guillaume Membré and Sébastien Fourreau
  • 45 min pour mettre son application à genoux : le guide complet du test de charge by Loïc Ortola and Mathilde Lorrain
  • Limits, Requests, QoS, PriorityClasses, on balaie ce que vous pensiez savoir sur le scheduling dans Kubernetes by Denis Germain and Quentin Joly
  • Agents intelligents, la nouvelle frontière des LLMs by Guillaume Laforge
  • Optimiser des UIs Web legacy dans un moteur de jeu AAA by Cédric Chariere Fiedler and Clément Grégoire
  • L'aspirant chevalier LynxJS peut-il détrôner monseigneur React Native et le duc de Flutter ? by Simon Bernardin
  • En JavaScript, il y a un paquet pour tout... et souvent pour rien. by Estéban Soubiran (it's me!)

And I already know I'll watch the recordings of some talks I missed.

Talk Highlights ​

At every conference, I really love to highlight a few talks I really enjoyed. This is based on the impact they had on me, the quality of the content, and the speakers' ability to engage the audience. This is also very personal and subjective.

• The future of routing with the Navigation API by Eduardo San Martin Morote

  This talk is really deep because there's little chance we'll have to play with the Navigation API directly. It's more an API for package authors than for end users, like Eduardo, who is the creator of Vue Router and Pinia. But I found it really important to understand why this API exists, the drawbacks of the current one, and the potential it has for the future.

  His slides are full of smart animations, making them really easy to follow.

  

• 45 min pour mettre son application à genoux : le guide complet du test de charge by Loïc Ortola and Mathilde Lorrain

  This talk was already in my highlights of Devoxx 2025. I'm including it again because I attended it at DevFest Nantes and really appreciated it. It's really impressive. They could talk for far more than 45 minutes. Time flies during their presentation; it's well-written and very accessible.

  

I highly recommend watching these talks.

My Talk ​

My talk was En JavaScript, il y a un paquet pour tout... et souvent pour rien. My slot was the last of the day, on Friday, October 17 at 16:50. I had the opportunity to play it multiple times, so stress wasn't a problem. However, after two long days, I was really tired. I rested for an hour just before my talk.

When I woke up, I drank an espresso and I was up and running again. And I still don't like coffee.

It's now time to go on stage.

Before I went on stage, Pierre introduced me. This is the first time I experienced this and it's really fun. He also made sure that everything was good with the setup. Thank you, Pierre!

Then, I went on stage and delivered my talk. A quick selfie with the audience and let's explain e18e! The amphitheater was really impressive: 800 seats! That's a lot and, by far, the biggest room I've ever spoken in.

Everything went well and people enjoyed it! Fifteen minutes is so short; it's over just when you start to feel good, but that's the way it is.

I really appreciated DevFest Nantes, certainly the best conference of the year!

Technical part, you can skip it if you're not interested.

For this conference, and like the previous ones, I used Inalia, the SaaS I'm building to make presentations more interactive. It works well,which seems normal, yet I'm always amazed to have been able to build a platform, by myself, that just works.

In less than fifteen minutes, more than 17,000 requests (25,000 in total, but 8,000 were cached by Cloudflare) hit my small €4 VPS (2 vCPU and 4 GB of RAM). No lag, no bugs.

For the most curious among you, here is the duration breakdown of the route used to send an emoji on my slide. At the peak, more than 100 people were trying to access the app at the same time.

Behind the scenes, the VPS is also running Plausible, which consumes a lot of RAM. I'm testing lighter alternatives. On the VPS monitoring, the CPU usage peaked at 87%, but the load average was still under control (0.73, 0.68, 0.61). After some tests using autocannon, the VPS was able to handle 41 req/s with 100 concurrent connections over 60 seconds when accessing an overview page. After some tweaks, I was able to increase the performance to 47 req/s, and once Plausible is shut down, I expect to increase it to 53 req/s. So yes, the VPS is small, but it's enough for now.