Dockerfile: Lint and prepare for multiarch

Signed-off-by: Manuel Rüger <[email protected]>

Dockerfile

@@ -1,6 +1,9 @@
 FROM golang:1.13-alpine as base
-ENV GOOS=linux CGO_ENABLED=0 GOARCH=amd64
-RUN apk --no-cache add git
+ARG ARCH=amd64
+ENV GOOS=linux \
+    CGO_ENABLED=0 \
+    GOARCH=${ARCH}
+RUN apk add --no-cache git
 WORKDIR /app
 
 COPY go.mod .
@@ -21,25 +24,25 @@ RUN go test -v ./...
 FROM base as acceptance
 COPY --from=builder /app/conftest /app/conftest
 
-RUN apk add --update npm bash
+RUN apk add --no-cache npm bash
 RUN npm install -g bats
 
 RUN bats acceptance.bats
 
 ## EXAMPLES STAGE ##
 FROM base as examples
-ENV TERRAFORM_VERSION=0.12.0-rc1 \
+ENV TERRAFORM_VERSION=0.12.28 \
     KUSTOMIZE_VERSION=2.0.3
 
 COPY --from=builder /app/conftest /usr/local/bin
 COPY examples /examples
 
-RUN apk add --update npm make git jq ca-certificates openssl unzip wget && \
-    cd /tmp && \
-    wget https://releases.hashicorp.com/terraform/${TERRAFORM_VERSION}/terraform_${TERRAFORM_VERSION}_linux_amd64.zip && \
-    unzip terraform_${TERRAFORM_VERSION}_linux_amd64.zip -d /usr/local/bin
+WORKDIR /tmp
+RUN apk add --no-cache npm make git jq ca-certificates openssl unzip wget && \
+    wget "https://releases.hashicorp.com/terraform/${TERRAFORM_VERSION}/terraform_${TERRAFORM_VERSION}_linux_amd64.zip" && \
+    unzip "terraform_${TERRAFORM_VERSION}_linux_amd64.zip" -d /usr/local/bin
 
-RUN wget -O /usr/local/bin/kustomize https://github.com/kubernetes-sigs/kustomize/releases/download/v${KUSTOMIZE_VERSION}/kustomize_${KUSTOMIZE_VERSION}_linux_amd64 && \
+RUN wget -O /usr/local/bin/kustomize "https://github.com/kubernetes-sigs/kustomize/releases/download/v${KUSTOMIZE_VERSION}/kustomize_${KUSTOMIZE_VERSION}_linux_amd64" && \
     chmod +x /usr/local/bin/kustomize
 
 RUN go get -u cuelang.org/go/cmd/cue