Use multi-stage docker build to reduce image size.

Dockerfile

@@ -1,25 +1,38 @@
-FROM ubuntu:eoan
+#
+# First stage - builder
+#
+FROM debian:10-slim AS builder
 
 ENV DEBIAN_FRONTEND noninteractive
 ENV LC_ALL C.UTF-8
 
-# This allows you to use a local Ubuntu mirror
-ARG APT_URL=
-ENV APT_URL ${APT_URL:-http://archive.ubuntu.com/ubuntu/}
-RUN sed -i "s%http://archive.ubuntu.com/ubuntu/%${APT_URL}%" /etc/apt/sources.list
-
+# This allows you to use a local Debian mirror
+ARG APT_URL=http://deb.debian.org/debian/
+ARG MAKE_FLAGS=-j2
 
-# Update packages and install dependencies
-RUN apt-get update && apt-get -y upgrade && apt-get -y clean
-RUN apt-get install -y protobuf-compiler libh2o-dev libcurl4-openssl-dev \
-        libssl-dev libprotobuf-dev libh2o-evloop-dev libwslay-dev libeigen3-dev libzstd-dev \
-	make gcc g++ git build-essential curl autoconf automake libfmt-dev libncurses5-dev \
-    && apt-get -y clean
+RUN sed -i "s%http://deb.debian.org/debian/%${APT_URL}%" /etc/apt/sources.list \
+    && apt-get update && apt-get -y upgrade \
+    && apt-get install -y protobuf-compiler libh2o-dev libcurl4-openssl-dev \
+           libssl-dev libprotobuf-dev libh2o-evloop-dev libwslay-dev \
+           libeigen3-dev libzstd-dev libfmt-dev libncurses-dev \
+           make gcc g++ git build-essential curl autoconf automake help2man
 
 # Build
-ARG MAKE_FLAGS=-j2
-ADD . /galmon/
-WORKDIR /galmon/
-RUN make $MAKE_FLAGS
-ENV PATH=/galmon:${PATH}
+ADD . /galmon-src/
+RUN cd /galmon-src/ \
+    && make $MAKE_FLAGS \
+    && prefix=/galmon make install
 
+#
+# Second stage - contains just the binaries
+#
+FROM debian:10-slim
+RUN apt-get update && apt-get -y upgrade \
+    && apt-get install -y libcurl4 libssl1.1 libprotobuf17 libh2o-evloop0.13 \
+           libncurses6 \
+    && apt-get -y clean \
+    && rm -rf /var/lib/apt/lists/*
+COPY --from=builder /galmon/ /galmon/
+ENV PATH=/galmon/bin:${PATH}
+ENV LC_ALL C.UTF-8
+WORKDIR /galmon/bin