Improve Dockerfile

Dockerfile

@@ -1,5 +1,21 @@
-FROM quay.io/prometheus/busybox:latest
+FROM golang:1.15-buster AS build
 
-COPY s3_exporter /bin/s3_exporter
+ADD . /tmp/s3_exporter
 
-ENTRYPOINT ["/bin/s3_exporter"]
+RUN cd /tmp/s3_exporter && \
+    echo "s3:*:100:s3" > group && \
+    echo "s3:*:100:100::/:/s3_exporter" > passwd && \
+    make
+
+
+FROM scratch
+
+COPY --from=build /etc/ssl/certs/ca-certificates.crt /etc/ssl/certs/
+COPY --from=build /tmp/s3_exporter/group \
+    /tmp/s3_exporter/passwd \
+    /etc/
+COPY --from=build /tmp/s3_exporter/s3_exporter /
+
+USER s3:s3
+EXPOSE 9340/tcp
+ENTRYPOINT ["/s3_exporter"]