Fastify not working in Docker

Josh Sherman
1 min read
Software Development

I’ve been using Express since it’s inception and while I’ve never really had any issues with it, I’m also always up for messing around with something new. That something new (to me at least) is Fastify.

A recent project of mine included building an extremely lightweight API to power some widgets and Slack notifications. This seemed like a good time to play around with Fastify and learn a bit about it.

While very similar to Express, it did feel like it was a bit lighter in terms of syntax to get up and running. Since this project was something small in nature, the speed improvements that Fastify touts probably won’t ever be noticed, let alone fully realized.

Where I ended up hitting a wall with Fastify is when I attempted to Dockerize the API I was building. Things ran just fine, but I wasn’t able to access the API at all.

After some investigation, specifically running nmap to verify that the port in question was in fact open, I started to think that perhaps it had something to do with the IP address binding within Docker.

This is something I’ve run into previously with webpack, so I had a good idea of where to start.

Fortunately, the fix was similar in nature and quite simple.

Inside of a Docker container, you need to explicitly bind some apps to the address To do so with Fastify, you just need to do the following.

Instead of doing this:

await fastify.listen({ port: 3000 })

You need to do this:

await fastify.listen({ host: '', port: 3000 });

And then you should be good to go to access your Dockerized Fastify service.

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Husband. Father. Pug dad. Musician. Founder of Holiday API, Head of Engineering and Emoji Specialist at Mailshake, and author of the best damn Lorem Ipsum Library for PHP.

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