Copy static files from Docker container to non empty named volume - docker

Question

I wanna copy new static files from Docker container via named volume to nginx container that has old static.
Prerequisites:
Host machine directory tree:
.
├── data
│   ├── bar.2.css
│   └── foo.2.js
├── docker-compose.yml
├── Dockerfile
Dockerfile:
FROM busybox:latest
COPY data /data
docker-compose.yml:
version: '3'
services:
static:
image: 'myimage'
volumes:
- 'myvolume:/data'
nginx:
image: 'nginx'
volumes:
- 'myvolume:/data'
volumes:
myvolume:
Directory tree of named volume myvolume with old static:
.
├── bar.1.css
└── foo.1.js
Sequence of steps:
Build myimage with Dockerfile: docker build -t myimage .
Check new static files in myimage: docker run myimage ls /data
bar.2.css
foo.2.js
Run: docker-compose up -d --build static
In my mind it must rebuild service static and overwrite old static files. But it did't. Why and how to fix it? Also, what is a better approach?

Answer 1

I think that you are just coping the new files alongside the old files with the docker build -t myimage .
Maybe you can delete the previous data before you insert new, by running a one-time container??
docker exec -it static rm /data
and then just copy the new data, or build the new image:
docker cp /data static:/data
You can also, implement the build step inside the docker-compose file:
version: '3'
services:
static:
build: /
image: 'myimage'
volumes:
- 'myvolume:/data'
nginx:
image: 'nginx'
volumes:
- 'myvolume:/data'
volumes:
myvolume:

Answer 2

Why -- I believe that you are mounting the pre-existing volume myvolume atop your /data folder of the static container. This is because your myvolume already exists. If myvolume did not exist, the content of /data would be copied to the volume.
See: Docker-Volume-Docs -- "If you start a container which creates a new volume, as above, and the container has files or directories in the directory to be mounted (such as /app/ above), the directory’s contents will be copied into the volume."
Sample Solution
Give this a shot. With the structure and content below do a:
docker-compose up --build
This is additive, so if you update/add content to the newdata folder and re-run your compose, then the new content will be present in the shared volume.
You can mount and inspect the shared volume, like this:
docker run -it --rm --mount type=volume,src={docker-volume-name},target=/shared busybox sh
Environment
Folder structure:
.
├── dockerfile
├── docker-compose.yml
├── newdata/
── apple.txt
── banana.txt
dockerfile
FROM busybox:latest
# From host machine to image
COPY newdata/* /newdata/
# #Runtime from image to where a shared volume could be mounted.
ENTRYPOINT [ "cp", "-r", "/newdata/", "/shared" ]
docker-compose.yml
version: '3.2'
services:
data-provider:
image: data-provider
build: .
volumes:
- type: volume
source: so
target: /shared
destination:
image: busybox:latest
volumes:
- type: volume
source: so
target: /shared-data
depends_on:
- data-provider
command: ls -la /shared-data/newdata
volumes:
so:
Sample Output:
$ docker-compose up --build
Creating volume "sodockervol_so" with default driver
Building data-provider
Step 1/3 : FROM busybox:latest
---> c75bebcdd211
Step 2/3 : COPY newdata/* /newdata/
---> bc85fc19ed7b
Removing intermediate container 2a39f4be8dd2
Step 3/3 : ENTRYPOINT cp -r /newdata/ /shared
---> Running in e755c3179b4f
---> 6e79a32bf668
Removing intermediate container e755c3179b4f
Successfully built 6e79a32bf668
Successfully tagged data-provider:latest
Creating sodockervol_data-provider_1 ...
Creating sodockervol_data-provider_1 ... done
Creating sodockervol_destination_1 ...
Creating sodockervol_destination_1 ... done
Attaching to sodockervol_data-provider_1, sodockervol_destination_1
destination_1 | total 16
destination_1 | drwxr-xr-x 2 root root 4096 Oct 9 17:50 .
destination_1 | drwxr-xr-x 3 root root 4096 Oct 9 17:50 ..
destination_1 | -rwxr-xr-x 1 root root 25 Oct 9 17:50 apple.txt
destination_1 | -rwxr-xr-x 1 root root 28 Oct 9 17:50 banana.txt
sodockervol_data-provider_1 exited with code 0
sodockervol_destination_1 exited with code 0