SSH Bastion Docker image

Usage

#

Some variables will be used here:

• $JUMPER_PORT - SSH port which will be used for jumping to another hosts. As port 22 most likely will be busy by system SSH daemon, we will use another port, for example 10022.
• $JUMPER_HOST - host which will be used as bastion, it may be dedicated server or part of your cluster. For examples we will use localhost.
• $JUMPER_USER - user which will be used to login on this host, something like developer or admin. By default it is jumper.

So, here is defaults:

1JUMPER_PORT=10022
2JUMPER_HOST=localhost
3JUMPER_USER=jumper

Quick way

#

1. Create your own image based on this image with following files:

   Dockerfile:

   1FROM docker.pkg.github.com/soar/sshbastion/sshbastion:latest
   

   homefs/.ssh/authorized_keys:

   1ssh-rsa AAAA... your first user rsa key
   2ssh-rsa AAAA... your second user rsa key
   

2. Build and run your image:

   1docker build -t mybastion .
   2docker run -p $JUMPER_PORT:$JUMPER_PORT -it mybastion
   

3. Test it with commands above

4. Deploy it on your infrastructure

Connecting

#

With port forwarding

#

1. Establish connection to bastion-host and open local port

   1ssh -N -L $LP:$TARGET_HOSTNAME:$TARGET_PORT -p $JUMPER_PORT $JUMPER_USER@$JUMPER_HOST
   

   where:

   • -N - not to try to allocate PTY
   • -L - local port redirection mode
   • $LP - local port to open (1024+ if you are not root)
   • $TARGET_HOSTNAME - target hostname to connect to
   • $TARGET_PORT - target port to connect to
   • $JUMPER_PORT, $JUMPER_USER, $JUMPER_HOST - see above

   for example:

   1# connect to another machine over SSH
   2ssh -N -L 2022:anotherhost.example.com:22 -p $JUMPER_PORT $JUMPER_USER@$JUMPER_HOST
   3# connect to remote MySQL server
   4ssh -N -L 13306:anotherhost.example.com:3306 -p $JUMPER_PORT $JUMPER_USER@$JUMPER_HOST
   

2. Connect via opened local port Now you can use any application forwarded in previous step, just use localhost:$LP as target. For example for SSH:

   1ssh -p $LP $REMOTE_USER@localhost
   

   where:

   • $LP - locally opened port from previous step
   • $REMOTE_USER - user to authenticate on target host
   • localhost - your address, where you’ve started tunnel

   for example:

   1# connect to another machine over SSH
   2ssh -p 2022 targetuser@localhost
   3# connect to remote MySQL server
   4mysql -u root -h localhost -P 13306
   

With SSH proxy-command

#

SSH will open tunnel for you automatically with next command:

1ssh -o ProxyCommand="ssh -W %h:%p -p $JUMPER_PORT $JUMPER_USER@$JUMPER_HOST" targetuser@$TARGET_HOSTNAME

For example:

1ssh -o ProxyCommand="ssh -W %h:%p -p 10022 jumper@localhost" [email protected]

Environment variables

#

• WHITELIST - comma-separated list of allowed IPs (or ranges in wildcard form) to connect.

  See: man 5 sshd_config / Match or Patterns section

  Examples:

  • 192.0.2.1
  • 192.0.2.1,192.0.2.2,192.0.2.3
  • 192.0.2.*,10.0.0.1
  • 192.0.2.0/24,10.0.0.0/24
  • 2001:db8::/32