sftp

SFTP service image with audit logs and gcsfuse that descends from atmoz/sftp.

Goals:

1. Run on Compute Engine with persistent backend
2. Audit log all user activity to STDOUT for view in Logging
3. Use SSH host key stored in Secret Manager

Added packages:

• gcsfuse
• rsyslog

Changed configuration:

• use imuxsock rsyslog module for shared log socket in chroots - ripped from aptible/docker-sftp
• comment out imklog rsyslog module
• symlink /usr/sbin/rsyslogd in to /etc/sftp.d/
• add -l INFO to sftp options for audit logging

Added scripts:

• /gcs_entrypoint - writes SSH host key files from env vars then execs original entrypoint. This script is set as the image ENTRYPOINT.
• /usr/local/sbin/sshd_tail_log - links shared log socket into each user chroot, runs /usr/sbin/sshd, tails /var/log/auth.log to STDOUT. This script is set as the image CMD.