Docker compose volumes_from not updating after rebuild - docker

Question

Imagine two containers: webserver (1) is hosting static HTML files that need to be built form templates inside a data volume container (2).
docker-compose.yml file looks something like this:
version: "2"
services:
webserver:
build: ./web
ports:
- "80:80"
volumes_from:
- templates
templates:
build: ./templates
Dockerfile for templates service looks like this
FROM ruby:2.3
# ... there is more but that is should not be important
WORKDIR /tmp
COPY ./Gemfile /tmp/Gemfile
RUN bundle install
COPY ./source /tmp/source
RUN bundle exec middleman build --clean
VOLUME /tmp/build
When I run docker-compose up everything is working as expected: templates are built, webserver hosts them and you can view them in the browser.
Problem is, when I update the ./source and restart/rebuild the setup, the files the webserver hosts are still the old ones, although the log shows that the container was rebuilt - at least the last three layers after COPY ./source /tmp/source. So the changes inside the source folder are picked up by the rebuilt but I'm not able to get the changes shown in the browser.
What am I doing wrong?

Answer 1

Compose preserves volumes when containers are recreated, which is probably why you are seeing the old files.
Generally it is not a good idea to use volumes for source code (or in this case static html files). Volumes are for data you want to persist, like data in a database. Source code changes with each version of the image, so doesn't really belong in a volume.
Instead of using a data volume container for these files, you can use a builder container to compile them and a webserver service to host them. You'll need to add a COPY to the webserver Dockerfile to include the files.
To accomplish this you would change your docker-compose.yml to this:
version: "2"
services:
webserver:
image: myapp:latest
ports: ["80:80"]
Now you just need to build myapp:latest. You could write a script which:
builds the builder container
runs the builder container
builds the myapp container
You can also use a tool like dobi instead of writing a script (disclaimer: I am the author of this tool). There is an example of building a minimal docker image which is very similar to what you're trying to do.
Your dobi.yaml might look something like this:
image=builder:
image: myapp-dev
context: ./templates
job=templates:
use: builder
image=webserver:
image: myapp
tags: [latest]
context: .
depends: [templates]
compose=serve:
files: [docker-compose.yml]
depends: [webserver]
Now if you run dobi serve it will do all the steps for you. Each step will only be run if files have changed.