images/go-runner/Dockerfile: Explicitly set 'direct' fallback in GOPROXY

From https://golang.org/doc/go1.15#go-command:

The GOPROXY environment variable now supports skipping proxies that
return errors. Proxy URLs may now be separated with either commas (,) or
pipe characters (|). If a proxy URL is followed by a comma, the go
command will only try the next proxy in the list after a 404 or 410 HTTP
response. If a proxy URL is followed by a pipe character, the go command
will try the next proxy in the list after any error. Note that the
default value of GOPROXY remains https://proxy.golang.org,direct, which
does not fall back to direct in case of errors.

Signed-off-by: Stephen Augustus <[email protected]>

Author: justaugustus

images/build/go-runner/Dockerfile

@@ -18,15 +18,12 @@ ARG DISTROLESS_IMAGE
 FROM golang:${GO_VERSION} as builder
 WORKDIR /workspace
 
-# Run this with docker build --build_arg goproxy=$(go env GOPROXY) to override the goproxy
-ARG goproxy=https://proxy.golang.org
-# Run this with docker build --build_arg package=./controlplane/kubeadm or --build_arg package=./bootstrap/kubeadm
-ENV GOPROXY=$goproxy
-
 # Copy the sources
 COPY ./go-runner.go ./
 COPY ./go.* ./
 
+ENV GOPROXY="https://proxy.golang.org|direct"
+
 # Cache the go build
 RUN go build .