faster and more efficient docker file

Dockerfile

@@ -1,23 +1,32 @@
-FROM alpine:latest as build
-
-ADD . /sslh
-
-RUN \
-  apk add \
-    gcc \
-    libconfig-dev \
-    make \
-    musl-dev \
-    pcre2-dev \
-    perl && \
-  cd /sslh && \
-  make sslh-select && \
-  strip sslh-select
-
-FROM alpine:latest
-
-COPY --from=build /sslh/sslh-select /sslh
-
-RUN apk --no-cache add libconfig pcre2
-
-ENTRYPOINT [ "/sslh", "--foreground"]
+##########################################################################################
+## BUILD APPLICATION
+##########################################################################################
+FROM alpine:latest as build
+
+# install required packages first to be able to take advantage of caching
+RUN apk add \
+  gcc \
+  libconfig-dev \
+  make \
+  musl-dev \
+  pcre2-dev \
+  perl
+
+# copy files and build the app
+WORKDIR /sslh
+ADD . .
+RUN make sslh-select && \
+  strip sslh-select
+
+
+##########################################################################################
+## PACKAGE APPLICATION
+##########################################################################################
+FROM alpine:latest
+
+# install required packages first and in parallel with the build container execution
+RUN apk --no-cache add libconfig pcre2
+
+# copy the final executable from the build container
+COPY --from=build /sslh/sslh-select /sslh
+ENTRYPOINT [ "/sslh", "--foreground"]