Mounted volume using volume-from is empty - ruby-on-rails

Question

So here's what I'm trying to do:
Nginx container linked to -> Rails container running Puma
Using docker-compose, this solution works great. I'm able to start both containers and the NGINX container has access to the volume in the linked container using volumes_from.
First, the relevant bits of the Dockerfile for Rails:
ENV RAILS_ROOT /www/apps/myapp
RUN mkdir -p $RAILS_ROOT
WORKDIR $RAILS_ROOT
.... lots of files get put in their proper places ....
EXPOSE 3000
VOLUME [/www/apps/myapp/]
CMD puma -C config/puma.rb
Nginx config is pretty basic, relevant parts are here:
ENV RAILS_ROOT /www/apps/myapp
# Set our working directory inside the image
WORKDIR $RAILS_ROOT
EXPOSE 80
EXPOSE 443
Again, this all works great in docker-compose. However, in ECS, I'm trying to use the following task definition:
{
"family": "myapp",
"containerDefinitions": [
{
"name": "web",
"image": "%REPOSITORY_URI%:nginx-staging",
"cpu": 512,
"memory": 512,
"portMappings": [
{
"containerPort": 80,
"protocol": "tcp"
},
{
"containerPort": 443,
"protocol": "tcp"
}
],
"links": [
"myapp"
],
"volumesFrom": [
{
"sourceContainer": "myapp",
"readOnly": false
}
],
"essential": true,
"logConfiguration": {
"logDriver": "awslogs",
"options": {
"awslogs-group": "awslogs-myapp-staging",
"awslogs-region": "us-west-2",
"awslogs-stream-prefix": "awslogs-myapp-nginx"
}
}
},
{
"image": "%REPOSITORY_URI%:v_%BUILD_NUMBER%",
"name": "myapp",
"cpu": 2048,
"memory": 2056,
"essential": true,
...bunch of environment variables, etc.
}
The task starts in ECS as expected, and the myapp container looks perfect. However, when I check out the nginx container on the EC2 instance host with
docker exec -it <container> bash
I land in /www/apps/myapp, but the directory is empty. I've tried to mount drives and do several other things and I'm at a loss here... anyone have any ideas as to how to get the files from the linked container to be usable in my nginx container?

Answer 1

And of course, right after I post this I find the solution. So no one else has to feel this pain, here it is:
VOLUME [/www/apps/myapp/]
VOLUME ["/www/apps/myapp/"]
sigh