proposal: IP modes

[progrium]

There are a lot of different ways to get an IP to register. This is a placeholder issue to flesh out a proposal for the various modes.

[andyshinn]

Some additional notes I had written down around this:

• Ability to get IP address from environment. Specify the environment variable that would contain the correct IP address (SERVICE_IP=$COREOS_PRIVATE_IPV4).
• Try looking up IP address by adapter if hostname fails.
• Separate out into different IP lookup models (adapter, environment variable, hostname, etc.).

[jefferai]

Specifying adapter is a quite common paradigm; ideally this would be a first-order possibility, not only if hostname fails. That can be a lot simpler than having to fix any logic mistakes by manually mapping IPs to hostnames in e.g. /etc/hosts.

[enxebre]

This just got merged on Docker and is relevant here as docker inspect will return list of networks now.
moby/moby#17360

[panga]

+1 to "Add ability to specify address by interface #129"

[wbyoung]

For what it's worth, I wrote a tiny wrapper to handle by network interface:

FROM gliderlabs/registrator:latest
COPY registrator-wrapper /bin/
ENTRYPOINT ["/bin/registrator-wrapper"]

#!/bin/sh

ip_args=""

if [ -n "$REGISTRATOR_NETWORK_INTERFACE" ]; then
  ip=$(
    ifconfig $REGISTRATOR_NETWORK_INTERFACE |
    grep 'inet addr:' |
    cut -d: -f2 |
    awk '{ print $1}'
  )
  ip_args="-ip $ip"
fi

/bin/registrator $ip_args "$@"