Docker Captain Take 5 — Julien Maitrehenry

Docker Captains are select members of the community that are both experts in their field and are passionate about sharing their Docker knowledge with others. “Docker Captains Take 5” is a regular blog series where we get a closer look at our Captains and ask them the same broad set of questions ranging from what their best Docker tip is to whether they prefer cats or dogs (personally, we like whales and turtles over here). Today, we’re interviewing Julien who recently joined the Captains Program. He is a developer and devops at Kumojin and is based in Quebec City.

Headshot of julien maitrehenry

How/when did you first discover Docker?

I don’t remember how, but, back in 2014, I was working in a PHP shop, and we had our dev environment running inside a VM (with Vagrant). But, it wasn’t really easy to share and maintain. So, we started experimenting with Docker for our dev env. After that, I learned about (legacy/classic) Swarm in Docker, and these tools resolved some of my issues in production for handling load balancer reconfiguration, deployment, and new version management. Check out my first conference about Docker here.

Since then, I continue to learn, use, and share about Docker. It’s useful in so many use cases — it’s amazing!

What is your favorite Docker command?

Docker help. I still need to check the documentation sometimes!

But also, when I need more space on Docker Desktop, I’ll choose docker buildx prune!

What is your top tip for working with Docker that others may not know?

If your team uses ARM (Apple M1, for example) and intel CPU and you want to share a docker image with your team, build a cross platform image:

docker buildx build --push --platform linux/arm64/v8,linux/amd64 --tag xxx/nginx-proxy:1.21-alpine

What’s the coolest Docker demo you have done/seen?

Back during the 2018 Dockercon, I was impressed by the usage of Docker for the DART (Double Asteroid Redirection Test) project. A project as easy as building an aircraft, hitting an asteroid with it, and saving the world!

You should check how they use Docker for space hardware emulation and testing — it’s brilliant to see how Docker could be used to help save the world:

What have you worked on in the past six months that you’re particularly proud of?

Being a mentor for a developer school in Quebec (42 Quebec). It’s amazing to see the new generation of developers and help them with all their questions, fears, and concerns! And it’s cool when someone calls you “Mister Docker” because he watches a docker conference I gave to answer questions about usage and more.

What do you anticipate will be Docker’s biggest announcement this year?

After Docker Extension and SBOM? It’s really hard to say. I need more time to explore and create my first extension, but, I’m sure the Docker team will find something.

What are some personal goals for the next year with respect to the Docker community?

Give my first conference in English as I always give them in French. I’d also like to update my blog with more content.

What was your favorite thing about DockerCon 2022?

The French community room. It was a pleasure to engage with Aurélie and Rachid and have so many great speakers with us! I would do it again anytime!

Looking to the distant future, what is the technology that you’re most excited about and that you think holds a lot of promise?

7 years from now, I still think Docker will continue to innovate and find new ways to simplify the life of the developer community!

Rapid fire questions…

What new skill have you mastered during the pandemic?

Using a face mask and forgetting about it! Or traveling between different countries during the pandemic with all different kinds of restrictions and rules.

Cats or Dogs?

Cats! I’m sorry, but a dog requires too much time, and I already have 3 young kids.

Salty, sour or sweet?

Salty or Umami

Beach or mountains?


Your most often used emoji?

🤣 or 😄


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