Madhav Puri 54240f8da9 Support for passing build-time variables in build context ... - The build-time variables are passed as environment-context for command(s) run as part of the RUN primitve. These variables are not persisted in environment of intermediate and final images when passed as context for RUN. The build environment is prepended to the intermediate continer's command string for aiding cache lookups. It also helps with build traceability. But this also makes the feature less secure from point of view of passing build time secrets. - The build-time variables also get used to expand the symbols used in certain Dockerfile primitves like ADD, COPY, USER etc, without an explicit prior definiton using a ENV primitive. These variables get persisted in the intermediate and final images whenever they are expanded. - The build-time variables are only expanded or passed to the RUN primtive if they are defined in Dockerfile using the ARG primitive or belong to list of built-in variables. HTTP_PROXY, HTTPS_PROXY, http_proxy, https_proxy, FTP_PROXY and NO_PROXY are built-in variables that needn't be explicitly defined in Dockerfile to use this feature. Signed-off-by: Madhav Puri <madhav.puri@gmail.com>		2015-09-16 03:31:15 -07:00
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command.go	Support for passing build-time variables in build context	2015-09-16 03:31:15 -07:00