add basic rsync server image

Dockerfile

@@ -3,3 +3,5 @@ FROM alpine:3.13
 RUN apk add --no-cache \
 	openssh-server \
 	rsync
+
+RUN mkdir -p /root/.ssh && cp /etc/ssh/sshd_config /etc/default_sshd_config

README.md

@@ -1,2 +1,11 @@
 # docker-rsync-server
 
+This is a simple docker image definition for starting an SSH server that is used for rsyncing to volume mounts.
+
+## Volumes
+
+| path                       | description                           |
+|----------------------------|---------------------------------------|
+| /root/.ssh/authorized_keys | the ssh keys to allow for auth        |
+| /etc/ssh                   | location for SSH host keys and config |
+| anywhere else              | the locations available for rsync     |

entrypoint.sh

@@ -3,6 +3,10 @@ set -eu
 
 ssh-keygen -A
 
+if [ ! -e '/etc/ssh/sshd_config' ]; then
+	cp /etc/default_sshd_config /etc/ssh/sshd_config
+fi
+
 /usr/sbin/sshd
 
 while pgrep -f /usr/sbin/sshd; do