Fixed #482: use dumb-init in docker for signal forwarding

Following-up on discussion in #488, now using https://github.com/Yelp/dumb-init
as entrypoint so our kiwix-* tools properly receives signals

docker/Dockerfile

@@ -12,22 +12,29 @@ ARG TARGETARCH
 ARG VERSION
 ARG ARCH
 
-# if we had no TARGETARCH (not buildx), use --build-arg ARCH. default to amd64
+# defaulting to amd64
 RUN echo "amd64" > /etc/docker_arch
+# use --build-arg ARCH if it was provided (not using buildx)
 RUN if [ ! -z "$ARCH" ] ; then echo "$ARCH" > /etc/docker_arch ; fi
+# use $TARGETARCH if provided.
 RUN if [ ! -z "$TARGETARCH" ] ; then echo "$TARGETARCH" > /etc/docker_arch ; fi
 
 # decide which kiwix arch to download later (`armhf` for all arm* and x86_64 otherwise)
 RUN if [ $(cut -c 1-3 /etc/docker_arch) = "arm" ] ; then echo "armhf" > /etc/kiwix_arch ; else echo "x86_64" > /etc/kiwix_arch ; fi
 
+# dumb-init to forward signals to PID=1
+RUN wget -q -O /usr/bin/dumb-init https://github.com/Yelp/dumb-init/releases/download/v1.2.5/dumb-init_1.2.5_x86_64 && \
+    chmod +x /usr/bin/dumb-init
+
 # Install kiwix-tools
 RUN url="http://mirror.download.kiwix.org/release/kiwix-tools/kiwix-tools_linux-$(cat /etc/kiwix_arch)-$VERSION.tar.gz" && \
     echo "URL: $url" && \
-    wget -O - $url | tar -xz && \
+    wget -q -O - $url | tar -xz && \
     mv kiwix-tools*/kiwix-* /usr/local/bin && \
     rm -r kiwix-tools*
 
 # expose kiwix-serve default port
 EXPOSE 80
 
+ENTRYPOINT ["/usr/bin/dumb-init", "--"]
 CMD ["/bin/sh", "-c", "echo 'Welcome to kiwix-tools! The following binaries are available:' && ls /usr/local/bin/"]

docker/server/Dockerfile

@@ -11,4 +11,4 @@ WORKDIR /data
 
 COPY ./start.sh /usr/local/bin/
 
-ENTRYPOINT ["/usr/local/bin/start.sh"]
+ENTRYPOINT ["/usr/bin/dumb-init", "--", "/usr/local/bin/start.sh"]