Add suitable init for running in a container

This goes with the experimental `docker` output format.

Signed-off-by: Justin Cormack <justin.cormack@docker.com>

pkg/init-container/Dockerfile

@@ -0,0 +1,14 @@
+FROM linuxkit/alpine:630ee558e4869672fae230c78364e367b8ea67a9 AS mirror
+RUN mkdir -p /out/etc/apk && cp -r /etc/apk/* /out/etc/apk/
+RUN apk add --no-cache --initdb -p /out alpine-baselayout busybox musl tini
+
+# Remove apk residuals. We have a read-only rootfs, so apk is of no use.
+RUN rm -rf /out/etc/apk /out/lib/apk /out/var/cache
+
+FROM scratch
+ENTRYPOINT []
+CMD []
+WORKDIR /
+COPY --from=mirror /out/ /
+COPY etc etc/
+COPY bin bin/

pkg/init-container/Makefile

@@ -0,0 +1,15 @@
+.PHONY: tag push
+default: push
+
+ORG?=mobytest
+IMAGE=init-container
+DEPS=Dockerfile $(wildcard etc/init.d/*) $(wildcard bin/*)
+
+HASH?=$(shell git ls-tree HEAD -- ../$(notdir $(CURDIR)) | awk '{print $$3}')
+
+tag: $(DEPS)
+	docker build --no-cache --network=none -t $(ORG)/$(IMAGE):$(HASH) .
+
+push: tag
+	DOCKER_CONTENT_TRUST=1 docker pull $(ORG)/$(IMAGE):$(HASH) || \
+	DOCKER_CONTENT_TRUST=1 docker push $(ORG)/$(IMAGE):$(HASH)

pkg/init-container/bin/rc.init

@@ -0,0 +1,10 @@
+#!/bin/sh
+
+# execute other init processes
+INITS="$(find /etc/init.d -type f | sort)"
+for f in $INITS
+do
+	$f &
+done
+
+wait

pkg/init-container/etc/init.d/010-containerd

@@ -0,0 +1,46 @@
+#!/bin/sh
+
+# set global ulimits TODO move to /etc/limits.conf
+ulimit -n 1048576
+ulimit -p unlimited
+
+# bring up containerd
+printf "\nStarting containerd\n"
+/usr/bin/containerd &
+
+# wait for socket to be there
+while [ ! -S /run/containerd/containerd.sock ]
+do
+	sleep 0.1
+done
+
+# start onboot containers, run to completion
+
+if [ -d /containers/onboot ]
+then
+	for f in $(find /containers/onboot -mindepth 1 -maxdepth 1 | sort)
+	do
+		base="$(basename $f)"
+		#/bin/mount --bind "$f/rootfs" "$f/rootfs"
+		#mount -o remount,rw "$f/rootfs"
+		/usr/bin/runc run --bundle "$f" "$(basename $f)"
+		printf " - $base\n"
+	done
+fi
+
+# start service containers
+
+if [ -d /containers/services ]
+then
+	for f in $(find /containers/services -mindepth 1 -maxdepth 1 | sort)
+	do
+		base="$(basename $f)"
+		#/bin/mount --bind "$f/rootfs" "$f/rootfs"
+		#mount -o remount,rw "$f/rootfs"
+		log="/var/log/$base.log"
+		ctr run --runtime-config "$f/config.json" --rootfs "$f/rootfs" --id "$(basename $f)" </dev/null 2>$log >$log &
+		printf " - $base\n"
+	done
+fi
+
+wait