SSH Server ( can be used as part of traefik ingress)

Background

I use Traefik to control access to my home network. For security I use https with multifactor authentication and for ssh this dockerimage uses public key authentication - password based authentication is disabled.

I didn't want to disable password authentication on my existing ssh services, so have created a docker container that disables inbound connection password authentication that can be used as the traefik ingress point before hopping to other computers.

Software

This dockerfile uses Alpine Linux to run an openssh server daemon.

Persistance

Two directories can optionally be exposed to the docker host system. Doing so will preserve the ssh servers host keys and the shell users ssh files. If you don't perist these directories, then you will have to trust the host id and re-add authorized keys every time the container is rebuilt.

File or Folder	Description
/etc/sshsavedhostkeys	entrypoint.sh saves or restores this ssh server keys as needed
/home/shelluser/.ssh	shelluser - The jump user's .ssh folder containing the the PKI key, authorized_keys and known_hosts

The image creates the sshd daemon's server keys in a mountable volume. This means that the container can be dropped, re-built, re-started without needing to issue and trust a new set of keys.

Quick command summary

Rebuild / run your own

docker stop sshd;docker rm sshd;docker build --tag sshd sshd

Pull from github

docker pull ghcr.io/stevegroom/sshd:latest

Start without persistance

docker run --name sshd --detach --port 122:22 sshd:latest
-or-
docker run --name sshd --detach --port 122:22 ghcr.io/stevegroom/sshd:latest

Start with persistance

docker run --name sshd \
 --detach \
 --publish 122:22 \
 --volume ~/sshserver/persist/sshsavedhostkeys:/etc/sshsavedhostkeys \
 --volume ~/sshserver/persist/shelluserssh:/home/shelluser/.ssh \
 sshd:latest

 -or-

docker run --name sshd \
 --detach \
 --publish 122:22 \
 --volume ~/sshserver/persist/sshsavedhostkeys:/etc/sshsavedhostkeys \
 --volume ~/sshserver/persist/shelluserssh:/home/shelluser/.ssh \
 ghcr.io/stevegroom/sshd:latest

Add your public keys to the shelluser authorized_keys

Repeat for all the keys you need to add

docker exec -it sshd /addauthuser.sh "$(cat ~/.ssh/id_rsa.pub)"

-or-

docker exec -it sshd /addauthuser.sh "ssh-rsa AAAAB3NzaC ... your id_rsa.pub ...GVVqApPd steve@slice.lan"

ssh into the jumpbox

ssh shelluser@dockerhost -p 122

ssh through the jumpbox to private servers

ssh -J shelluser@dockerhost:122 user@privatehost -p 22

Look inside the ssh server

docker exec -it sshd  /bin/sh
vi /etc/ssh/sshd_config

Operations

chmod 600 persist/authorized_keys

Backup

To make a sharable backup - omit saving the keys:

tar -czvf sshserver.tar.gz --exclude sshserver/persist/shelluserssh/* --exclude sshserver/persist/sshsavedhostkeys/* sshserver 

References

Locking sshd to auth keys only

https://techblog.thcb.org/how-to-install-openssh-server-on-alpine-linux-including-docker/

Using sshd as a jump box

Edit the sshd config file to allow port forwarding.

https://www.ssh.com/academy/ssh/tunneling/example

Contributors