k8s prototype.

Dockerfile.dind

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+FROM docker:19.03
+
+# https://github.com/docker/docker/blob/master/project/PACKAGERS.md#runtime-dependencies
+RUN set -eux; \
+	apk add --no-cache \
+		btrfs-progs \
+		e2fsprogs \
+		e2fsprogs-extra \
+		iptables \
+		openssl \
+		shadow-uidmap \
+		xfsprogs \
+		xz \
+# pigz: https://github.com/moby/moby/pull/35697 (faster gzip implementation)
+		pigz \
+	; \
+# only install zfs if it's available for the current architecture
+# https://git.alpinelinux.org/cgit/aports/tree/main/zfs/APKBUILD?h=3.6-stable#n9 ("all !armhf !ppc64le" as of 2017-11-01)
+# "apk info XYZ" exits with a zero exit code but no output when the package exists but not for this arch
+	if zfs="$(apk info --no-cache --quiet zfs)" && [ -n "$zfs" ]; then \
+		apk add --no-cache zfs; \
+	fi
+
+# TODO aufs-tools
+
+# set up subuid/subgid so that "--userns-remap=default" works out-of-the-box
+RUN set -x \
+	&& addgroup -S dockremap \
+	&& adduser -S -G dockremap dockremap \
+	&& echo 'dockremap:165536:65536' >> /etc/subuid \
+	&& echo 'dockremap:165536:65536' >> /etc/subgid
+
+# https://github.com/docker/docker/tree/master/hack/dind
+ENV DIND_COMMIT ed89041433a031cafc0a0f19cfe573c31688d377
+
+RUN set -eux; \
+	wget -O /usr/local/bin/dind "https://raw.githubusercontent.com/docker/docker/${DIND_COMMIT}/hack/dind"; \
+	chmod +x /usr/local/bin/dind
+
+COPY dockerd-entrypoint.sh /usr/local/bin/
+
+VOLUME /var/lib/docker
+EXPOSE 6788 6789
+
+ENTRYPOINT ["dockerd-entrypoint.sh"]
+CMD []