lxd-ssh: wrapper for using ssh/scp/etc with lxd

lxd-ssh.sh

#!/bin/sh
set -e

# lxd-ssh
# Wrapper for using ssh/scp/etc with lxd
# Author: Robie Basak <robie.basak@canonical.com>
# Last-Update: 2017-10-11

# Instructions:
#
# 1) Use "lxc profile edit default" or similar to put a cloud-init snippet that
#    gives permission to your ssh public key in new instances.
#
#    Example:
#    $ lxc profile edit default
#          config:
#            user.user-data: |
#              #cloud-config
#              ssh_authorized_keys:
#                - ssh-rsa AAAA...
#
# 2) Put this script (lxd-ssh) somewhere; ideally in your path
#
# 3) Then put something like the following in ~/.ssh/config:
#        Hostname *.lxd
#            User ubuntu
#            ProxyCommand lxd-ssh %h
#
# Now the following should Just Work:
#     $ lxc launch ubuntu:xenial foo
#     Creating foo
#     Starting foo
#     $ ssh foo.lxd
#     ...
#     ubuntu@foo:~$
#
# scp, git remotes and other ssh-using commands should Just Work too.
#
# Known issues:
# 1) It takes a few moments for the container to create its host key and start
#    sshd. Until then attempts to ssh will result in an error.

hostname="$1"
case "$hostname" in
    *.lxd) ;;
    *)
        echo "Hostname supplied ($hostname) does not end in .lxd"
        exit 1
        ;;
esac

container=${hostname%.lxd}

sync_host_keys() {
    local hostname=$1
    local container=$2

    cleanup() { rm -rf "$tmpdir"; }
    tmpdir=`mktemp -d lxd-ssh.XXXXX`
    trap cleanup INT TERM
    lxc exec "$container" -- sh -c 'cat /etc/ssh/*.pub 2>/dev/null || echo "Container ssh host keys not found; has it had enough time to boot?" >&2' | while read a b c; do echo -n "$hostname ";echo "$a $b";done > "$tmpdir/known_hosts_additions" && \
    	ssh-keygen -H -f "$tmpdir/known_hosts_additions" 2>/dev/null && \
            cat ~/.ssh/known_hosts "$tmpdir/known_hosts_additions" > ~/.ssh/known_hosts.$$ && \
            mv ~/.ssh/known_hosts.$$ ~/.ssh/known_hosts
    cleanup
}

if ! ssh-keygen -F "$hostname" </dev/null >/dev/null; then
    sync_host_keys "$hostname" "$container" </dev/null >/dev/null
fi

exec lxc exec "$container" -- sshd -i