Setup Docker Container with SSH server?

Question

I want to setup a very minimalistic alpine linux docker container with the following capabilities:

• It runs an ssh server
• It copies over a SSH public key of my choice to which I can then authenticate

I looked into various options, and in the end decided to write my own small Dockerfile. However, I ran into some problems.

Dockerfile

FROM alpine:latest

RUN apk update
RUN apk upgrade
RUN apk add openssh-server

RUN mkdir -p /var/run/sshd
RUN mkdir -p /root/.ssh

ADD authorized_keys /root/.ssh/authorized_keys
ADD entrypoint.sh /entrypoint.sh
RUN chmod 755 /entrypoint.sh

EXPOSE 22
CMD ["/entrypoint.sh"]

entrypoint.sh

#!/bin/sh
/usr/sbin/sshd -D

authorized_keys

ecdsa-sha2-nistp256 AAAAE2VjZHNhLXNoYTItbmlzdHAyNTYAAAAIbmlzdHAyNTYAAABBBP8cIHIPgV9QoAaSsYNGHktiP/QnWfKPOeyzjujUXgQMQLBw3jJ1EBe04Lk3FXTMxwrKk3Dxq0VhJ+Od6UwzPDg=

Starting the container gives an error: sshd: no hostkeys available -- exiting. How can I fix my Dockerfile, to ensure the ssh server is running correctly and the authorized_keys file is there. What am I missing?