add VERSION build arg

Dockerfile

@@ -1,17 +1,19 @@
 FROM alpine AS build
 
 ARG TARGETPLATFORM
+ARG VERSION
 
-RUN apk add --update curl jq
+RUN if [ -z "$VERSION" ]; then echo "VERSION is required" && exit 1; fi
+
+RUN apk add --update curl
 
 RUN arch=$(echo ${TARGETPLATFORM} | cut -d/ -f2) \
-  && tarball=$(curl 'https://pkgs.tailscale.com/stable/?mode=json' | jq -r .Tarballs.${arch}) \
-  && version=$(echo ${tarball} | cut -d_ -f2) \
-  && curl "https://pkgs.tailscale.com/stable/${tarball}" -o tailscale.tgz \
+  && tarball=tailscale_${VERSION}_${arch} \
+  && curl -f "https://pkgs.tailscale.com/stable/${tarball}.tgz" -o tailscale.tgz \
   && tar xzf tailscale.tgz \
   && mkdir -p /root-layer/usr/bin /root-layer/usr/sbin \
-  && cp -vrf "tailscale_${version}_${arch}"/tailscale /root-layer/usr/bin/tailscale \
-  && cp -vrf "tailscale_${version}_${arch}"/tailscaled /root-layer/usr/sbin/tailscaled
+  && cp -vrf "${tarball}/tailscale" /root-layer/usr/bin/tailscale \
+  && cp -vrf "${tarball}/tailscaled" /root-layer/usr/sbin/tailscaled
 
 COPY root/ /root-layer/