host-local IP address management plugin

host-local IPAM allocates IPv4 and IPv6 addresses out of a specified address range. Optionally, it can include a DNS configuration from a resolv.conf file on the host.

Overview

host-local IPAM plugin allocates ip addresses out of a set of address ranges. It stores the state locally on the host filesystem, therefore ensuring uniqueness of IP addresses on a single host.

The allocator can allocate multiple ranges, and supports sets of multiple (disjoint) subnets. The allocation strategy is loosely round-robin within each range set.

Example configurations

Note that the key ranges is a list of range sets. That is to say, the length of the top-level array is the number of addresses returned. The second-level array is a set of subnets to use as a pool of possible addresses.

This example configuration returns 2 IP addresses.

{
	"ipam": {
		"type": "host-local",
		"ranges": [
			[
				{
					"subnet": "10.10.0.0/16",
					"rangeStart": "10.10.1.20",
					"rangeEnd": "10.10.3.50",
					"gateway": "10.10.0.254"
				},
				{
					"subnet": "172.16.5.0/24"
				}
			],
			[
				{
					"subnet": "3ffe:ffff:0:01ff::/64",
					"rangeStart": "3ffe:ffff:0:01ff::0010",
					"rangeEnd": "3ffe:ffff:0:01ff::0020"
				}
			]
		],
		"routes": [
			{ "dst": "0.0.0.0/0" },
			{ "dst": "192.168.0.0/16", "gw": "10.10.5.1" },
			{ "dst": "3ffe:ffff:0:01ff::1/64" }
		],
		"dataDir": "/run/my-orchestrator/container-ipam-state"
	}
}

Previous versions of the host-local allocator did not support the ranges property, and instead expected a single range on the top level. This is deprecated but still supported.

{
  "ipam": {
		"type": "host-local",
		"subnet": "3ffe:ffff:0:01ff::/64",
		"rangeStart": "3ffe:ffff:0:01ff::0010",
		"rangeEnd": "3ffe:ffff:0:01ff::0020",
		"routes": [
			{ "dst": "3ffe:ffff:0:01ff::1/64" }
		],
		"resolvConf": "/etc/resolv.conf"
	}
}

We can test it out on the command-line:

$ echo '{ "cniVersion": "0.3.1", "name": "examplenet", "ipam": { "type": "host-local", "ranges": [ [{"subnet": "203.0.113.0/24"}], [{"subnet": "2001:db8:1::/64"}]], "dataDir": "/tmp/cni-example"  } }' | CNI_COMMAND=ADD CNI_CONTAINERID=example CNI_NETNS=/dev/null CNI_IFNAME=dummy0 CNI_PATH=. ./host-local

{
    "ips": [
        {
            "version": "4",
            "address": "203.0.113.2/24",
            "gateway": "203.0.113.1"
        },
        {
            "version": "6",
            "address": "2001:db8:1::2/64",
            "gateway": "2001:db8:1::1"
        }
    ],
    "dns": {}
}

Network configuration reference

• type (string, required): “host-local”.
• routes (string, optional): list of routes to add to the container namespace. Each route is a dictionary with “dst” and optional “gw” fields. If “gw” is omitted, value of “gateway” will be used.
• resolvConf (string, optional): Path to a resolv.conf on the host to parse and return as the DNS configuration
• dataDir (string, optional): Path to a directory to use for maintaining state, e.g. which IPs have been allocated to which containers
• ranges, (array, required, nonempty) an array of arrays of range objects:
  • subnet (string, required): CIDR block to allocate out of.
  • rangeStart (string, optional): IP inside of “subnet” from which to start allocating addresses. Defaults to “.2” IP inside of the “subnet” block.
  • rangeEnd (string, optional): IP inside of “subnet” with which to end allocating addresses. Defaults to “.254” IP inside of the “subnet” block for ipv4, “.255” for IPv6
  • gateway (string, optional): IP inside of “subnet” to designate as the gateway. Defaults to “.1” IP inside of the “subnet” block.

Older versions of the host-local plugin did not support the ranges array. Instead, all the properties in the range object were top-level. This is still supported but deprecated.

Supported arguments

The following CNI_ARGS are supported:

• ip: request a specific IP address from a subnet.

The following args conventions are supported:

• ips (array of strings): A list of custom IPs to attempt to allocate

The following Capability Args are supported:

• ipRanges: The exact same as the ranges array - a list of address pools

Custom IP allocation

For every requested custom IP, the host-local allocator will request that IP if it falls within one of the range objects. Thus it is possible to specify multiple custom IPs and multiple ranges.

If any requested IPs cannot be reserved, either because they are already in use or are not part of a specified range, the plugin will return an error.

Files

Allocated IP addresses are stored as files in /var/lib/cni/networks/$NETWORK_NAME. The path can be customized with the dataDir option listed above. Environments where IPs are released automatically on reboot (e.g. running containers are not restored) may wish to specify /var/run/cni or another tmpfs mounted directory instead.