Leverage Docker Layer System (#1191)

Dockerfile best practices recommend to move the installation of external dependencies before specific code.
This will improve local development experience by improving Docker cache management
and it will improve final Docker images compaction by sharing the first layers.

Dockerfile

@@ -1,9 +1,13 @@
 FROM ubuntu:20.04
 
 ARG TARGETARCH
-COPY ./dist/${TARGETARCH}/ttyd /usr/bin/ttyd
+
+# Dependencies
 RUN apt-get update && apt-get install -y --no-install-recommends tini && rm -rf /var/lib/apt/lists/*
 
+# Application
+COPY ./dist/${TARGETARCH}/ttyd /usr/bin/ttyd
+
 EXPOSE 7681
 WORKDIR /root
 

Dockerfile.alpine

@@ -1,9 +1,13 @@
 FROM alpine
 
 ARG TARGETARCH
-COPY ./dist/${TARGETARCH}/ttyd /usr/bin/ttyd
+
+# Dependencies
 RUN apk add --no-cache bash tini
 
+# Application
+COPY ./dist/${TARGETARCH}/ttyd /usr/bin/ttyd
+
 EXPOSE 7681
 WORKDIR /root