Add a retry loop with BatchMode=yes to absorb the race window
between Env.Start() returning (when tta reports the tailscale
backend as Running) and cloud-init finishing the user/SSH-key
setup. In CI, the second VM's tta agent has been observed
connecting only a few hundred milliseconds before the test SSHes
in, which is inside the window where /root/.ssh/authorized_keys
hasn't fully landed yet. SSH key auth then fails and ssh(1) falls
back to interactive password prompts (3x), wasting time and
producing a confusing "Permission denied (publickey,password)"
error.
BatchMode=yes makes the client fail fast on auth failure instead
of prompting, and the retry loop handles SSH transport-level
errors (exit code 255) for up to 30 seconds with 500ms backoff.
Remote command non-zero exits still pass through unchanged.
Fixes#20228
Signed-off-by: Brad Fitzpatrick <bradfitz@tailscale.com>
Change-Id: I17f7422e9e27bf7b995f505c0184cbb2b230ed81
Brad FitzpatrickandBrad Fitzpatrick
0bc0cb8131