Minor change to the Dockerfile to improve build speed (#1139)

"go mod download" does not depend on the VERSION env var, so moving the ARG directive after the RUN will allow better use of the Docker build cache - subsequent builds on the same machine need only re-run the "go mod download" if go.mod or go.sum has changed, rather than re-running it any time the VERSION value passed from the Makefile has changed

Co-authored-by: Joel Speed <Joel.speed@hotmail.co.uk>

Dockerfile

@@ -1,5 +1,4 @@
 FROM golang:1.16-buster AS builder
-ARG VERSION
 
 # Copy sources
 WORKDIR $GOPATH/src/github.com/oauth2-proxy/oauth2-proxy
@@ -11,6 +10,8 @@ RUN GO111MODULE=on go mod download
 # Now pull in our code
 COPY . .
 
+ARG VERSION
+
 # Build binary and make sure there is at least an empty key file.
 #  This is useful for GCP App Engine custom runtime builds, because
 #  you cannot use multiline variables in their app.yaml, so you have to

Dockerfile.arm64

@@ -1,5 +1,4 @@
 FROM golang:1.16-buster AS builder
-ARG VERSION
 
 # Copy sources
 WORKDIR $GOPATH/src/github.com/oauth2-proxy/oauth2-proxy
@@ -11,6 +10,8 @@ RUN GO111MODULE=on go mod download
 # Now pull in our code
 COPY . .
 
+ARG VERSION
+
 # Build binary and make sure there is at least an empty key file.
 #  This is useful for GCP App Engine custom runtime builds, because
 #  you cannot use multiline variables in their app.yaml, so you have to

Dockerfile.armv6

@@ -1,5 +1,4 @@
 FROM golang:1.16-buster AS builder
-ARG VERSION
 
 # Copy sources
 WORKDIR $GOPATH/src/github.com/oauth2-proxy/oauth2-proxy
@@ -11,6 +10,8 @@ RUN GO111MODULE=on go mod download
 # Now pull in our code
 COPY . .
 
+ARG VERSION
+
 # Build binary and make sure there is at least an empty key file.
 #  This is useful for GCP App Engine custom runtime builds, because
 #  you cannot use multiline variables in their app.yaml, so you have to