musteresel's blog

Open a console connection to a Xen VM

2017-07-11

tagged: xen

I need to setup some virtual machines running on a Xen server which don’t have a ssh server running yet. One can access such VMs easily with Xen management software like XenCenter, but I prefer the UNIX philosophy “do one thing and do it well” and instead have a tool to do just that: give me a connection to one console of one virtual machine of some Xen server.

It took me a while to dig out the correct Xen API calls, but description of consoles of the xapi-project sums it up pretty well. In short:

  1. Login at the Xen server to create new session with Session.login_with_password

  2. Get a reference to the virtual machine, e.g. by name with VM.get_by_name_label

  3. Get a list of consoles of that VM: VM.get_consoles

  4. Find a console with protocol vt100 by looking at console.get_protocol

  5. Get the “location” of the console: console.get_location

  6. Depending on the locations protocol …

    • if it’s https, then use gnutls-cli or openssl s_client, …
    • otherwise (http) using telnet is sufficient to connect to the location’s host

  7. Encode username and password for authorization:

    echo -n "user:pass" | base64

  8. send, with CR-LF line endings and two empty lines at the end:

    CONNECT <location> HTTP/1.1
Authorization: Basic <encoded-user-pass>

  9. use connection as vt100 terminal.

Doing this manually on the command line actually worked pretty well, except the terminal was “crippled” (the local terminal probably needs to be configured somehow, probably like done in miniterm). It worked good enough to install an ssh server, though.

The same should work with VNC consoles, too. Then I could setup a local port and redirect any traffic to the remote connection which I previously would set up like described above. Any VNC viewer should then be able to connect to my local port.

Also note that - contrary to the Xen API docs (shipped with the Xen SDK) - one needs to make the HTTP connect request with HTTP/1.1 (got the idea to try this from this only partly related discussion).