Docker: Dockerfile improvements

- Format adjustments
 - Fix error: missing runtime dependencies

docker/alpine/Dockerfile

@@ -14,47 +14,45 @@ ENV DNS_ADDR_2  8.8.4.4
 ENV ARGS=
 
 COPY . /tmp/repo
-
-RUN set -ex && \
-    apk add --no-cache --virtual .build-deps \
-                                autoconf \
-                                automake \
-                                build-base \
-                                c-ares-dev \
-                                libev-dev \
-                                libtool \
-                                libsodium-dev \
-                                linux-headers \
-                                mbedtls-dev \
-                                pcre-dev && \
-    cd /tmp/repo && \
-    ./autogen.sh && \
-    ./configure --prefix=/usr --disable-documentation && \
-    make install && \
-
-    runDeps="$( \
-        scanelf --needed --nobanner /usr/bin/ss-* \
-            | awk '{ gsub(/,/, "\nso:", $2); print "so:" $2 }' \
-            | xargs -r apk info --installed \
-            | sort -u \
-    )" && \
-    apk add --no-cache --virtual .run-deps \
-                                rng-tools \
-                                $runDeps && \
-    apk del .build-deps && \
-    rm -rf /tmp/repo
+RUN set -ex \
+ # Build environment setup
+ && apk add --no-cache --virtual .build-deps \
+      autoconf \
+      automake \
+      build-base \
+      c-ares-dev \
+      libev-dev \
+      libtool \
+      libsodium-dev \
+      linux-headers \
+      mbedtls-dev \
+      pcre-dev \
+ # Build & install
+ && cd /tmp/repo \
+ && ./autogen.sh \
+ && ./configure --prefix=/usr --disable-documentation \
+ && make install \
+ && apk del .build-deps \
+ # Runtime dependencies setup
+ && apk add --no-cache \
+      rng-tools \
+      $(scanelf --needed --nobanner /usr/bin/ss-* \
+      | awk '{ gsub(/,/, "\nso:", $2); print "so:" $2 }' \
+      | sort -u) \
+ && rm -rf /tmp/repo
 
 USER nobody
 
 EXPOSE 8388/tcp 8388/udp
 
-CMD ss-server -s $SERVER_ADDR \
-              -p 8388 \
-              -k ${PASSWORD:-$(hostname)} \
-              -m $METHOD \
-              -t $TIMEOUT \
-              --fast-open \
-              -d $DNS_ADDR \
-              -d $DNS_ADDR_2 \
-              -u \
-              $ARGS
+CMD exec ss-server \
+      -s $SERVER_ADDR \
+      -p 8388 \
+      -k ${PASSWORD:-$(hostname)} \
+      -m $METHOD \
+      -t $TIMEOUT \
+      --fast-open \
+      -d $DNS_ADDR \
+      -d $DNS_ADDR_2 \
+      -u \
+      $ARGS