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This is a base Docker image for Scala applications, specifically web services. Currently this image will have installed:

  • Java 8
  • Scala 2.11.7
  • SBT 0.13.9

This image is build off of baseimage-docker, which provides an init system and process supervisor called runit for starting and monitoring services.

This image is available on Dockerhub (here)


It is recommended that the Dockerfile be located in the root of the project source directory. This way, the ADD . /cromwell line below is a good convention for adding the project source code to the Docker container.

Within the project's source tree are two Docker-related files:

  • docker/ - A script that is invoked to compile the source code on the container.
  • docker/ - A script that is invoked by runit to start the service. This is optional. If scala-baseimage is not being used to host a server then this can be omitted.
FROM broadinstitute/scala-baseimage

# Cromwell's HTTP Port

# Current working directory contains the project source code
ADD . /cromwell
RUN ["/bin/bash", "-c", "/cromwell/docker/ /cromwell"]

# Add Cromwell as a service (it will start when the container starts)
RUN mkdir /etc/service/cromwell
ADD docker/ /etc/service/cromwell/run

Using the Docker Container

Run docker build . from this directory to build scala-baseimage. If it is successful, it'll print out the image ID at the end:

$ docker build .
Sending build context to Docker daemon  76.8 kB
Step 0 : FROM phusion/baseimage:0.9.17
 ---> e9f50c1887ea
Successfully built a5f889590f04

The container is meant to be run in detached mode (-d flag for docker run). Scala-baseimage has a proper init system as it's PID 1 process, so the container doesn't immediately exit.

To get a Bash shell on the container:

$ docker run -t -i a5f889590f04 bash -l

NOTE: This replaces the normal PID 1 process with a bash -l process, so any services set up in runit will not run.

To run a persistent container:

$ docker run -d a5f889590f04

NOTE: This does start up services set up in runit, but if those services are listening on a port, that port should be exposed via an EXPOSE <port> in the Dockerfile as well as a -p flag to docker run

To get a Bash shell on the prior persistent container:

$ docker exec -t -i 0623e6ebdfd30d0511b4ee8e56fe32c5d6d99ed436a65b23d1857921822e15f6 bash -l

Using Runit

The PID 1 process will launch Runit which will in turn start all services that are in /etc/service. This can be better visualized by seeing the process tree within the Docker container:

To control the services, use the sv command. The man pages are available from the container but one might have to do apt-get update; apt-get install man to get access to them.

# sv status cromwell
run: cromwell: (pid 17) 147672s
# sv down cromwell
# sv up cromwell

NOTE: sv down doesn't necessarily kill the underlying Java process. It might have been orphaned and inherited by PID 1 because it might not respond to signals that Runit is sending it properly. This would cause a subsequent sv up of that service to act weird (e.g. ports would be conflicting). After doing an sv down, if the process isn't dead, kill it with kill.

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