docker-compose volumes not working this way - docker-compose

Question

in my docker-compose.yml , I am using the registry:2 image ( version)
as I need to set up my own configuration ( for using S3 storage ) , I tried to mound my config directory in place of the default one
/usr/share/docker-registry/config/config.yml # my own registry config in local host
/go/src/github.com/docker/distribution/cmd/registry/config.yml # default in container
in my docker-compose.yml , I wrote
backend:
image: registry:2
ports:
- 127.0.0.1:5000:5000
links:
- cache
volumes:
- /usr/share/docker-registry/config:/go/src/github.com/docker/distribution/cmd/registry
..
but when I compose it, my config settings are never taken in account... it's always using the default settings in the container cmd/registry/config.yml
what could be wrong ?
If I inspect the running registry:v2 container , I can see that
thanks for any enlightenment ...
If I inspect the running registry:v2 container , the config is weird ( S3 info are there, but no volumes , and the CMD is executing the standard config.yml file ... )
"Config": {
"Hostname": "5337012111a5",
"Domainname": "",
"User": "",
"AttachStdin": false,
"AttachStdout": false,
"AttachStderr": false,
"PortSpecs": null,
"ExposedPorts": {
"5000/tcp": {}
},
"Tty": false,
"OpenStdin": false,
"StdinOnce": false,
"Env": [
"SETTINGS_FLAVOR=local",
"REGISTRY_STORAGE_S3_SECURE=True",
"REGISTRY_STORAGE_S3_ENCRYPT=True",
"REGISTRY_STORAGE_S3_ROOTDIRECTORY=/s3/object/name/prefix",
"CACHE_REDIS_PORT=6379",
"REGISTRY_STORAGE_S3_V4AUTH=True",
"REGISTRY_STORAGE_S3_CHUNKSIZE=5242880",
"REGISTRY_STORAGE_S3_SECRETKEY=yyyyyyyyyyyyyyyyyyyyyyyy”,
"CACHE_LRU_REDIS_PORT=6379",
"SEARCH_BACKEND=sqlalchemy",
"CACHE_REDIS_HOST=cache",
"REGISTRY_STORAGE_S3_ACCESSKEY=xxxxxxxxxxxxxxxxxxxxxxxxxxxxxx”,
"CACHE_LRU_REDIS_HOST=cache",
"REGISTRY_STORAGE_S3_REGION=eu-central-1",
"REGISTRY_STORAGE_S3_BUCKET=harbor.dufour16.net",
"PATH=/go/bin:/usr/src/go/bin:/usr/local/sbin:/usr/local/bin:/usr/sbin:/usr/bin:/sbin:/bin",
"GOLANG_VERSION=1.4.2",
"GOPATH=/go/src/github.com/docker/distribution/Godeps/_workspace:/go",
"DISTRIBUTION_DIR=/go/src/github.com/docker/distribution"
],
"Cmd": [
"cmd/registry/config.yml"
],
"Image": "registry:2",
"Volumes": null,
"VolumeDriver": "",
"WorkingDir": "/go/src/github.com/docker/distribution",
"Entrypoint": [
"registry"
],

Answer 1

I need to override settings with environment variables.. not using external volumes ..