dhcp plugin

Overview

With dhcp plugin the containers can get an IP allocated by a DHCP server already running on your network. This can be especially useful with plugin types such as macvlan . Because a DHCP lease must be periodically renewed for the duration of container lifetime, a separate daemon is required to be running. The same plugin binary can also be run in the daemon mode.

Operation

To use the dhcp IPAM plugin, first launch the dhcp daemon:

# Make sure the unix socket has been removed
$ rm -f /run/cni/dhcp.sock
$ ./dhcp daemon

If given -pidfile <path> arguments after ‘daemon’, the dhcp plugin will write its PID to the given file.
If given -hostprefix <prefix> arguments after ‘daemon’, the dhcp plugin will use this prefix for DHCP socket as <prefix>/run/cni/dhcp.sock. You can use this prefix for references to the host filesystem, e.g. to access netns and the unix socket.
If given -broadcast=true argument after ‘daemon’, the dhcp plugin will enable the broadcast flag on DHCP packets.
If given -timeout <duration> arguments after ‘daemon’, the dhcp daemon will time out unanswered dhcp requests after this duration, defaults to 10s.

Alternatively, you can use systemd socket activation protocol. Be sure that the .socket file uses /run/cni/dhcp.sock as the socket path.

With the daemon running, containers using the dhcp plugin can be launched.

DHCP Options

Not all DHCP options are supported when requesting from server. Current supported are:

• ip-address, subnet-mask
• static-routes, classless-static-routes, routers
• dhcp-lease-time, dhcp-renewal-time, dhcp-rebinding-time

See man:dhcp-options(5) for description of these names. Also, you can use option ID instead of names, like 121 for classless-static-routes.

Example configuration

For example, to send hostname to the DHCP server when using Podman runtime, use this config:

{
    "ipam": {
        "type": "dhcp",
        "daemonSocketPath": "/run/cni/dhcp.sock",
        "request": [
            {
                "skipDefault": false
            }
        ],
        "provide": [
            {
                "option": "host-name",
                "fromArg": "K8S_POD_NAME"
            }
        ]
    }
}

Network configuration reference

• type (string, required): “dhcp”
• daemonSocketPath (string, optional): Path to the socket of daemon. If -hostprefix is set for the daemon, this value should be set to <prefix>/run/cni/dhcp.sock.
• request (dict, optional): Options requesting from DHCP server.
  • skipDefault (bool, optional): If the default request list is skipped.
  • option (string, optional): String or number representation of the DHCP option.
• provide (dict, optional): Options providing to DHCP server when acquire leases.
  • option (string, optional): String or number representation of the DHCP option.
  • value (string, optional): String representation of the value. Directly sent to server.
  • fromArg (string, optional): Get value from CNI_ARGS by given argument name.