Docker Compose to build a single service w/o Dockerfile

docker-compose.yml

services:
    8u121-jre-alpine:
        command:
            - /entrypoint.sh
        ports:
            - '9000:9000'
            - '9443:9443'
        image: openjdk:8u121-jre-alpine
        volumes:
            - ./entrypoint.sh:/entrypoint.sh:ro
            - ./svc:/svc:ro
version: '3'

entrypoint.sh

#!/usr/bin/env sh
# Generic entrypoint.sh for all containers.
set -ex
trap 'echo "Client shutting down" && exit' INT TERM

pacman=exit
if [ -x /sbin/apk ] ; then
    pacman='apk --no-cache add'
elif [ -x /usr/bin/yum ]; then
    # Amazon Linux (Yum-based) doesn't have an OpenJDK image.
    pacman='yum -y install java-1.8.0-openjdk-headless'
elif [ -x /usr/bin/apt-get ]; then
    apt-get update
    pacman='apt-get -y install'
fi
$pacman bash curl openssl rsync

# Clients won't have /svc. Play writes to this directory, so copy it.
cd /
if [ -x svc/bin/start ] ; then
    rsync -a /svc/ /mysvc/
fi

if [ -x /mysvc/bin/start ] ; then
    exec /mysvc/bin/start -Dhttps.port=9443 -Dplay.crypto.secret=secret
else
    while echo Client sleeping... ; do sleep 300 ; done
fi