Unpack Flyway in a separate build step

[TheSench]

Adding the .tar.gz file in one layer and unpacking it in a second layer adds a lot of bloat to the image size.

Moving the unpacking and permissions to a separate build step allows the final Flyway image to be much smaller (from 627MB to 447MB on my machine).

[TheSench]

Implementation notes:

[TheSench]

Note

All that the original steps did was copy the .tar.gz into the container, unpack it, and set permissions on it. We can simply do all of that in a build stage and then copy the resulting files into this container to avoid the cost of the extra layers.

[TheSench]

Note

I originally picked this image to ensure that users were exactly the same between the build image and the production image.

Now that I look at this a second time, I see that we're not changing ownership of any files, so that shouldn't actually matter. We could use a much smaller image like alpine here, but since the actual flyway image also uses this as its base, this is more efficient from a layers-downloaded perspective because this doesn't add any additional layers that we weren't already downloading for the flyway stage.

[Barry-RG]

Thank you for your PR. I am currently looking at a wider optimization of the docker images in Flyway and something similar to this is in the works.