Mount the mandatory config files separately in docker-compose, since it's including the whole /app from host and therefore the copies made in Dockerfile aren't available.

docker-compose.yml

@@ -13,7 +13,9 @@ services:
       DATABASE_USERNAME: root
       DATABASE_PASSWORD_EMPTY: 1
     volumes:
-      - ${VOLUME:-.:/app}:Z
+      - ${VOLUME:-.}:/app:Z
+      - ${VOLUME:-.}/config/database.docker.yml:/app/config/database.yml:Z
+      - ${VOLUME:-.}/config/site.docker.yml:/app/config/site.yml:Z
     ports:
       - 3000:3000
     depends_on:

script/docker-environment

@@ -2,12 +2,14 @@
 
 set -e
 
+echo "Doing it here"
+
 # Find our app dir
 appdir=$(cd $(dirname "$0")/.. && pwd)
 
 # Check if we've been told to run the command in Docker Composer.
 cmd="$@"; [ "$#" -eq 0 ] && cmd=bash
-export VOLUME="$appdir:/app"
+export VOLUME="$appdir"
 image=${DOCKER_IMAGE:=web}
 
 port_publish=""; [ "${BIND_DOCKER_SERVICE_PORTS:-}" = 1 ] && port_publish="--service-ports"