[baremetal] Add dispatcher script to statically configure DHCP address

[cybertron]

We have a feature request for nodes to be able to initially get
assigned their IP addresses via infinite DHCP leases, but then to
have those addresses statically configured on the node so that if
the DHCP server is unavailable for any reason they don't lose their
network configuration.

This adds a dispatcher script for NetworkManager that does so. It
looks at the DHCP assigned network settings and adds static
configuration with the same values.

- What I did

- How to verify it

- Description for the changelog

[cybertron]

/hold

This is a PoC. If we decide to pursue this it will almost certainly need some refinement.

[celebdor]

Does this not exist in IPv6?

[cybertron]

I only implemented ipv4 in this version. Based on my discussion with the NM team, I would probably argue that for this use case in ipv6 we should just use SLAAC addressing. If there's a reason we can't do that then we can always add support for DHCPv6 here too.

[cybertron]

/hold cancel

I've tested this locally with infinite DHCP leases and it worked fine.

[celebdor]

/retest

[cybertron]

/hold

We discovered that this would cause problems on reboot. Fix coming.

[celebdor]

Just tested it with a small modification on one of my masters with openshift-sdn. It worked well. Here some snippets:

mode: 0755
path: "/etc/NetworkManager/dispatcher.d/30-static-dhcp"
contents:
  inline: |
    #!/bin/bash
    set -ex -o pipefail
    if [[ "{{ .NetworkType }}" == "OVNKubernetes" && "$CONNECTION_ID" == "Wired Connection" ]]
    then
        >&2 echo "Refusing to modify default connection."
        exit 0
    fi

    if [ -z ${DHCP4_IP_ADDRESS:-} ]; then
        >&2 echo "Not a DHCP4 address. Ignoring."
        exit 0
    fi
    if [ ${DHCP4_DHCP_LEASE_TIME:-0} -lt 4294967295 ]; then
        >&2 echo "Not an infinite DHCP4 lease. Ignoring."
        exit 0
    fi
    IPS=($IP4_ADDRESS_0)
    CIDR=${IPS[0]}
    GATEWAY=${IPS[1]}
    TYPE=$(nmcli --get-values connection.type connection show "$CONNECTION_ID")
    if ! nmcli con show inf-lease-to-static
    then
        nmcli con add type "$TYPE" con-name inf-lease-to-static
    fi
    nmcli con mod inf-lease-to-static \
      conn.interface "$1" \
      connection.autoconnect yes \
      ipv4.addresses "$CIDR" \
      ipv4.method manual \
      ipv4.gateway "$GATEWAY" \
      ipv4.dns "$IP4_NAMESERVERS"
    if [ -n "$IP4_DOMAINS" ]; then
        nmcli con mod inf-lease-to-static ipv4.dns-search "$IP4_DOMAINS"
    fi
    plus=''
    for i in $(seq 0 $(($IP4_NUM_ROUTES-1)) )
    do
        varname="IP4_ROUTE_$i"
        nmcli con mod inf-lease-to-static ${plus}ipv4.routes "${!varname}"
        plus='+'
    done
    nmcli con up inf-lease-to-static
    # Copy it from the OverlayFS mount to the persistent lowerdir
    cp "/etc/NetworkManager/system-connections-merged/inf-lease-to-static.nmconnection" /etc/NetworkManager/system-connections

    if [ -n "${DHCP4_HOST_NAME:-}" ]
    then
        hostnamectl set-hostname --static --transient "$DHCP4_HOST_NAME"
    fi

After making these changes, that make sure that it works for openshift SDN and for OVN kubernetes, you can see in the following image that there is a reboot of master-0 (I also rebooted master-1) after I had killed the dnsmasq that provided DHCP functionality.
You can also see that the nodes boot up with the hostname they are supposed and become ready again.

[cybertron]

/hold cancel

I also had success rebooting nodes with the latest version of this. I think it's good to go.

[celebdor]

/lgtm

The version in this PR now matches what I tested successfully in #2188 (comment)

[sinnykumari]

overall lgtm.
/approve

[openshift-ci-robot]

[APPROVALNOTIFIER] This PR is APPROVED

This pull-request has been approved by: celebdor, cybertron, sinnykumari

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[sinnykumari]

/retest

[celebdor]

/retest