Better use of ARG and ENV combination

comanage-registry/Dockerfile.template

@@ -20,22 +20,10 @@ FROM php:7.0-apache
 ARG COMANAGE_REGISTRY_VERSION=%%COMANAGE_REGISTRY_VERSION%%
 ARG COMANAGE_REGISTRY_SRC_URL=https://github.com/Internet2/comanage-registry/archive/$COMANAGE_REGISTRY_VERSION.tar.gz
 
-# Default values for first administrator bootstrapped
-# into the platform, most likely overridden at build time
-# using build arguments.
-ARG COMANAGE_REGISTRY_ADMIN_GIVEN_NAME=Registry
-ARG COMANAGE_REGISTRY_ADMIN_FAMILY_NAME=Admin
-ARG COMANAGE_REGISTRY_ADMIN_USERNAME=registry.admin
-ARG COMANAGE_REGISTRY_ENABLE_POOLING=No
-
 LABEL comanage_registry_version=$COMANAGE_REGISTRY_VERSION
 LABEL comanage_registry_src_url=$COMANAGE_REGISTRY_SRC_URL
 
 ENV COMANAGE_REGISTRY_DIR /srv/comanage-registry
-ENV COMANAGE_REGISTRY_ADMIN_GIVEN_NAME ${COMANAGE_REGISTRY_ADMIN_GIVEN_NAME}
-ENV COMANAGE_REGISTRY_ADMIN_FAMILY_NAME ${COMANAGE_REGISTRY_ADMIN_FAMILY_NAME}
-ENV COMANAGE_REGISTRY_ADMIN_USERNAME ${COMANAGE_REGISTRY_ADMIN_USERNAME}
-ENV COMANAGE_REGISTRY_ENABLE_POOLING ${COMANAGE_REGISTRY_ENABLE_POOLING}
 
 RUN apt-get update && apt-get install -y \
          libldap-2.4-2 \
@@ -100,4 +88,17 @@ WORKDIR /var/www/html
 
 EXPOSE 80 443
 
+# Default values for first administrator bootstrapped
+# into the platform, most likely overridden at build time
+# using build arguments.
+ARG COMANAGE_REGISTRY_ADMIN_GIVEN_NAME
+ARG COMANAGE_REGISTRY_ADMIN_FAMILY_NAME
+ARG COMANAGE_REGISTRY_ADMIN_USERNAME
+ARG COMANAGE_REGISTRY_ENABLE_POOLING
+
+ENV COMANAGE_REGISTRY_ADMIN_GIVEN_NAME ${COMANAGE_REGISTRY_ADMIN_GIVEN_NAME:-Registry}
+ENV COMANAGE_REGISTRY_ADMIN_FAMILY_NAME ${COMANAGE_REGISTRY_ADMIN_FAMILY_NAME:-Admin}
+ENV COMANAGE_REGISTRY_ADMIN_USERNAME ${COMANAGE_REGISTRY_ADMIN_USERNAME:-registry.admin}
+ENV COMANAGE_REGISTRY_ENABLE_POOLING ${COMANAGE_REGISTRY_ENABLE_POOLING:-No}
+
 CMD ["apache2-foreground"]