Docker SBT

SBT is the de-facto build tool used for Scala. This is a Docker image for SBT based on Alpine to get as small an image as possible.

Tags

The tags, 1.2.8, 1.2, 1 and latest, all point to the same image. The full version tags like 0.12.4, 0.13.18 and 1.0.4 point to the older releases of SBT. 0.12, 0.13, 1.0 and 1.1 (along with 1.2) point to their respective latest minor releases. I am planning to maintain a latest version and a older release for a certain version category. This basically means that for 1.0 minor release, we will keep around 1.0.3 and 1.0.4 patch releases. For people who do not update their SBT versions often, I would recommend you use the minor release tags, rather than the full release tags with the patch version (meaning use 1.0 vs 1.0.4), because those would always be available.

Usage

You can run Scala through SBT using:

docker run --rm -it aa8y/sbt:latest sbt console

But the image is expected to be used more often as a base image for testing or packaging Scala code. While any of the tags could be used, I would recommend using latest, stable or the minor/major version tags. Using full version tags is not recommended because, such older tags maybe removed as new versions are released. Also, post version 1.0.0, SBT pulls the required SBT JARs based on the the SBT version specified in the project/build.properties file where the project directory is in the same directory as your based build.sbt file. This is what the entry should look like for example,

sbt.version=0.13.13

See this link for more details.

Also, Docker builds an image by building layers which are cached. So if the image is built the correct way, every little change won't rebuild the complete image. See the examples.

Examples

better-files: The .circleci/config.yml is an example on how these images could be used with CircleCI 2.0 as it inherently supports Docker.
scrypto: The Dockerfile is a good example of how to cache certain image layers to avoid rebuilding the image every time. Also, the .travis.yml file describes how to use the Docker image for running tests.

FAQs

Docker `RUN` commands used to run fine before but now I get a `Permission denied` error.

I recently changed the image to use another base image which has a non-root user called docker. So when you use this image as the base for another, you would have to explicitly run it as root by running USER root before running any commands which would require root access.

Why can't I use the `ci` tag anymore?

git and openssh have been added to all based images negating the need to have a special ci tag. Due to this the ci tag which was deprecated on Jan 13, 2019 has been removed on Apr 14, 2019.

Why is the `stable` tag no longer available?

Initially when I added the stable tag I was expecting to have Docker images for unstable/nightly SBT builds. Since I don't see that happening, the stable tag which was deprecated on Jab 13, 2019 was removed on Apr 14, 2019.

The `Dockerfile` did not have a version before. What does the new v1.0.0 release mean?

Since labels are now supported in Dockerfiles, the idea is to use Semantic Versioning for all changes. Also, I believe the image is stable enough to warrant a v1 release.

aa8y/docker-sbt

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