How to create a Dockerfile for your deno fresh project

Sometimes creating a Dockerfile is an art, you need to be aware of what files include in each layer to leverage the docker cache. How can we do this with deno fresh?

Recommended or usual Dockerfile

Most of the examples I have found in the internet (like this one) tend to copy all the files in the same Docker instruction:

FROM denoland/deno:2.1.4

WORKDIR /app

COPY . .
RUN deno cache main.ts
RUN deno task build

USER deno
EXPOSE 8000

CMD ["run", "-A", "main.ts"]

This of course works, but we are just copying all the files in the Docker image, and that can cause many issues:

Inclusion of files that are not needed.
Inclusion of dangerous files.

Of course you could argue that that is why we should we using a .dockerignore file, however, we are not caching almost anything in the Dockerfile. We could it better, although more verbose.

My approach

FROM denoland/deno:2.1.4

WORKDIR /app

COPY deno.json deno.json
COPY dev.ts dev.ts

COPY fresh.config.ts fresh.config.ts
COPY fresh.gen.ts fresh.gen.ts

COPY tailwind.config.ts tailwind.config.ts

COPY main.ts main.ts

COPY components components
COPY islands islands
COPY static static

COPY lib lib
COPY tests tests

RUN deno cache main.ts
RUN deno task build

USER deno
EXPOSE 8000

CMD ["run", "-A", "main.ts"]

I know it looks longer, and more verbose, but I like explicit code. I do not want to deal with copying the .git or tmp folder by mistake, and finding that the docker images is leaking information that should not.

All folders and files but lib and tests are mandatory for deno fresh. Those are for my application and test code (resp.). You can name them in the way you like.

As you see here, most of the time we will rely on the docker cache when building the image. Most of the time the configuration files are not modified at all, and this approach would save us some precious time.

Conclusion

Having a explicit code (even in Dockerfiles) makes my life easier. Make sure you understand how the docker cache works when building a docker image, and leverage that power.