Reuse of the existing Neutron networks

The current Kuryr implementation assumes the Neutron networks, subnetpools, subnets and ports are created by Kuryr and their lifecycles are completely controlled by Kuryr. However, in the case where users need to mix the VM instances and/or the bare metal nodes with containers, the capability of reusing existing Neutron networks for implementing Kuryr networks becomes valuable.

Problem Description

The main use case being addressed in this spec is described below:

  • Use of existing Neutron network and subnet resources created independent of Kuryr

With the addition of Tags to neutron resources Add tags to neutron resources spec the association between container networks and Neutron networks is implemented by associating tag(s) to Neutron networks. In particular, the container network ID is stored in such tags. Currently the maximum size for tags is 64 bytes. Therefore, we currently use two tags for each network to store the corresponding Docker ID.

Proposed Change

This specification proposes to use the Options that can be specified by user during the creation of Docker networks. We propose to use either the Neutron network uuid or name to identify the Neutron network to use. If the Neutron network uuid or name is specified but such a network does not exist or multiple such networks exist in cases where a network name is specified, the create operation fails. Otherwise, the existing network will be used. Similarly, if a subnet is not associated with the existing network it will be created by Kuryr. Otherwise, the existing subnet will be used.

The specified Neutron network is tagged with a well known string such that it can be verified whether it already existed at the time of the creation of the Docker network or not.

Proposed Workflow

  1. A user creates a Docker network and binds it to an existing Neutron network by specifying it’s uuid:

    $ sudo docker network create --driver=kuryr --ipam-driver=kuryr \
           --subnet --gateway --ip-range \
           -o \
    $ sudo docker network create --driver=kuryr --ipam-driver=kuryr \
           --subnet --gateway --ip-range \
           -o \

    This creates a Docker network with the given name, foo in this case, by using the Neutron network with the specified uuid or name.

    If subnet information is specified by --subnet, --gateway, and --ip-range as shown in the command above, the corresponding subnetpools and subnets are created or the existing resources are appropriately reused based on the provided information such as CIDR. For instance, if the network with the given UUID in the command exists and that network has the subnet whose CIDR is the same as what is given by --subnet and possibly --ip-range, Kuryr doesn’t create a subnet and just leaves the existing subnets as they are. Kuryr composes the response from the information of the created or reused subnet.

    It is expected that when Kuryr driver is used, the Kuryr IPAM driver is also used.

    If the gateway IP address of the reused Neutron subnet doesn’t match with the one given by --gateway, Kuryr returns the IP address set in the Neutron subnet nevertheless and the command is going to fail because of Dockers’s validation against the response.

  2. A user inspects the created Docker network

    $ sudo docker network inspect foo
        "Name": "foo",
        "Id": "286eddb51ebca09339cb17aaec05e48ffe60659ced6f3fc41b020b0eb506d364",
        "Scope": "global",
        "Driver": "kuryr",
        "IPAM": {
            "Driver": "kuryr",
            "Config": [{
                "Subnet": "",
                "IPRange": "",
                "Gateway": ""
        "Containers": {}
        "Options": {
            "": {
                "": "25495f6a-8eae-43ff-ad7b-77ba57ed0a04"

    A user can see the Neutron uuid given in the command is stored in the Docker’s storage and can be seen by inspecting the network.

  3. A user launches a container and attaches it to the network

    $ CID=$(sudo docker run --net=foo -itd busybox)

    This process is identical to the existing logic described in Kuryr devref. libnetwork calls /IpamDriver.RequestAddress, /NetworkDriver.CreateEndpoint and then /NetworkDriver.Join. The appropriate available IP address shall be returned by Neutron through Kuryr and a port with the IP address is created under the subnet on the network.

  4. A user terminates the container

    $ sudo docker kill ${CID}

    This process is identical to the existing logic described in Kuryr devref as well. libnetwork calls /IpamDriver.ReleaseAddress, /NetworkDriver.Leave and then /NetworkDriver.DeleteEndpoint.

  5. A user deletes the network

    $ sudo docker network rm foo

    When an existing Neutron network is used to create a Docker network, it is tagged such that during the delete operation the Neutron network does not get deleted. Currently, if an existing Neutron network is used, the subnets associated with it (whether pre existing or newly created) are preserved as well. In the future, we may consider tagging subnets themselves or the networks (with subnet information) to decide whether a subnet is to be deleted or not.