Ignition output only logged to primary console

[bgilbert]

Issue Report

Bug

Container Linux Version

$ cat /etc/os-release
NAME="Container Linux by CoreOS"
ID=coreos
VERSION=1520.0.0
VERSION_ID=1520.0.0
BUILD_ID=2017-08-30-0000
PRETTY_NAME="Container Linux by CoreOS 1520.0.0 (Ladybug)"
ANSI_COLOR="38;5;75"
HOME_URL="https://coreos.com/"
BUG_REPORT_URL="https://issues.coreos.com"
COREOS_BOARD="amd64-usr"

Environment

Bare metal, OpenStack, possibly others

Expected Behavior

Ignition logs are presented on the serial console.

Actual Behavior

Ignition logs are not presented on the serial console.

Reproduction Steps

1. Boot a machine with an invalid Ignition config.
2. Look for errors on the serial console.

Other Information

Kernel messages are logged to both primary and secondary consoles, but /dev/console output only goes to the primary console. On OEMs that use the default console settings, VGA is primary and ttyS0 is secondary.

Ignition could also log to kmsg, but that would expose Ignition logs (including the config) to any process that can run dmesg, which may not be desirable. One option is to teach Ignition to buffer logs and send them to kmsg only in case of failure, since in that case we won't be booting anyway.