zrhoffman commented on a change in pull request #5252:
URL: https://github.com/apache/trafficcontrol/pull/5252#discussion_r524736078
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File path: infrastructure/cdn-in-a-box/optional/vnc/Dockerfile
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@@ -14,15 +14,22 @@
# KIND, either express or implied. See the License for the
# specific language governing permissions and limitations
# under the License.
-FROM docker.io/centos:7
+
+ARG CENTOS_VERSION=8
+FROM centos:${CENTOS_VERSION}
+ARG CENTOS_VERSION=8
Review comment:
It's not a duplicate `ARG`. `ARG` is the only Dockerfile instruction
that is allowed before `FROM`, and in order to pull the image
`centos:${CENTOS_VERSION}` where `CENTOS_VERSION` is a build arg, `ARG` needs
to go before `FROM`.
However, build args (unlike environment variables) are not accessible in
build stages after the one where the build arg is declared. So, in order to be
able to use `CENTOS_VERSION` *after* the `FROM` instruction, a second `ARG`
instruction is required for `CENTOS_VERSION`.
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