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Remember to Include the Dockerfile in Your .dockerignore


My Dockerfiles typically look like the following:

FROM gradle:jdk11 AS builder
WORKDIR /home/root/
COPY . .
RUN gradle build -x test

The key point to notice is the COPY . . line which copies everything under the docker build context.

This is typically the root of the project being built. To optimize this process typically a .dockerignore is used which includes any files that docker must ignore when creating the build context.

Today I ran into an issue where I was trying to get a new Dockerfile working but every time I made a change to the Dockerfile and nowhere else, the entire image was rebuilt. Dockerfiles are normally in the root of the project it belongs to and COPY . . copies the root of said project. It turns out I did not have my Dockerfile in the .dockerignore. As soon as I added it changes to the Dockerfile did not result in a full image rebuild - only the modified lines caused a partial rebuild.