distribution: registry config problem

If I set an env config, registry won’t parse the config in my config file.

env config:

      REGISTRY_STORAGE: s3
      REGISTRY_STORAGE_S3_ACCESSKEY: ${REGISTRY_STORAGE_S3_ACCESSKEY}
      REGISTRY_STORAGE_S3_SECRETKEY: ${REGISTRY_STORAGE_S3_SECRETKEY}
      REGISTRY_STORAGE_S3_BUCKET: ${REGISTRY_STORAGE_S3_BUCKET}
      REGISTRY_STORAGE_S3_REGION: ${REGISTRY_STORAGE_S3_REGION}
#      REGISTRY_STORAGE_CACHE_BLOBDESCRIPTOR: redis

config file:

version: 0.1
storage:
  filesystem:
    rootdirectory: /var/lib/registry
  delete:
    enabled: true
  cache:
    blobdescriptor: redis
http:
  addr: 0.0.0.0:5000
  debug:
    addr: 0.0.0.0:5001
redis:
  addr: redis:6379

If I turn on the comment, the registry will not use redis as its blob descriptor:

registry_1  | time="2017-12-06T06:32:34Z" level=info msg="Starting upload purge in 53m0s" go.version=go1.7.6 instance.id=d2ee585b-e082-4d4c-a435-bd62a8711af9 version=v2.6.2
registry_1  | time="2017-12-06T06:32:34Z" level=info msg="listening on [::]:5000, tls" go.version=go1.7.6 instance.id=d2ee585b-e082-4d4c-a435-bd62a8711af9 version=v2.6.2

If I turn off the comment, it works:

registry_1  | time="2017-12-06T06:27:48Z" level=info msg="Starting upload purge in 58m0s" go.version=go1.7.6 instance.id=b96d0204-25b2-4c1f-bbba-1007ea47aa5e version=v2.6.2
registry_1  | time="2017-12-06T06:27:48Z" level=info msg="using redis blob descriptor cache" go.version=go1.7.6 instance.id=b96d0204-25b2-4c1f-bbba-1007ea47aa5e version=v2.6.2
registry_1  | time="2017-12-06T06:27:48Z" level=info msg="listening on [::]:5000, tls" go.version=go1.7.6 instance.id=b96d0204-25b2-4c1f-bbba-1007ea47aa5e version=v2.6.2

But interestingly, registry use the delete.enable part and ignored the cache.