flake plus docker cli metadata

Dockerfile

@@ -1,4 +1,26 @@
-FROM golang:1.19-alpine AS build
+# syntax = docker/dockerfile:1.4
+FROM nixos/nix:latest AS builder
+
+WORKDIR /tmp/build
+RUN mkdir /tmp/nix-store-closure
+
+RUN \
+    --mount=type=cache,target=/nix,from=nixos/nix:latest,source=/nix \
+    --mount=type=cache,target=/root/.cache \
+    --mount=type=bind,target=/tmp/build \
+    <<EOF
+  ls -l /nix/store | wc
+  nix \
+    --extra-experimental-features "nix-command flakes" \
+    --extra-substituters "http://host.docker.internal?priority=10" \
+    --option filter-syscalls false \
+    --show-trace \
+    --log-format raw \
+    build . --out-link /tmp/output/result
+  cp -R $(nix-store -qR /tmp/output/result) /tmp/nix-store-closure
+EOF
+
+FROM scratch
 
 WORKDIR /app