Specification for local Neutron plugin
1. What is the problem Part of the networking automation functionality is implemented in the Nova-APIGW, which bring coupling between Neutron and Nova servers. Users must deploy Nova-APIGW if they want to use the networking automation function, which is not flexible. 2. What is the solution to the problem Move the process of networking automation from the Nova-APIGW to local Neutron plugin. This specification covers the detailed introduction and discussion of this plugin. 3. What the features need to be implemented to the Tricircle to realize the solution The local Neutron plugin discussed in this specification needs to be implemented. Change-Id: I6450ab0d2103eb8fd6fa8869ae80376a37ae371a
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specs/ocata/local-neutron-plugin.rst
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specs/ocata/local-neutron-plugin.rst
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==============================
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Tricircle Local Neutron Plugin
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==============================
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Background
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==========
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One of the key value we would like to achieve via the Tricircle project is to
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provide networking automation functionality across several OpenStack instances.
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Each OpenStack instance runs its own Nova and Neutron services but shares the
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same Keystone service or uses federated Keystone, which is a multi-region
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deployment mode. With networking automation, virtual machines or bare metals
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booted in different OpenStack instances can inter-communicate via layer2 or
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layer3 network.
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Considering the cross OpenStack layer2 network case, if Neutron service in each
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OpenStack instance allocates ip address independently, the same ip address
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could be assigned to virtual machines in different OpenStack instances, thus ip
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address conflict could occur. One straightforward solution to this problem is
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to divide the ip allocation pool into several parts and each OpenStack instance
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has one. The drawback is that since virtual machines are not distributed evenly
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in each OpenStack instance, we may see some OpenStack instances uses up ip
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addresses while other OpenStack instances still have ip addresses not
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allocated. What's worse, dividing the ip allocation pool makes it impossible
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for us to process virtual machine migration from one OpenStack instance to
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another.
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Thanks to Neutron's flexible plugin framework, by writing a new plugin and
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configuring Neutron server to use it, developers can define what Neutron server
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should do after receiving a network resources operation request. So for the
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ip address conflict issue discussed above, we decide to run one central Neutron
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server with the Tricircle central Neutron plugin(abbr: "central plugin") to
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manage ip allocation pool centrally.
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Besides central plugin, we need a bridge to connect central and local Neutron
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servers since each OpenStack instance has its own local Nova and Neutron server
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but these two services are not aware of the central Neutron server. This bridge
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should validate requested network data via the central Neutron server, then
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create necessary network resources in the target OpenStack instance with the
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data retrieved from the central Neutron server.
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Local Plugin
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============
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For connecting central and local Neutron servers, Neutron plugin is again a
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good place for us to build the bridge. We can write our own plugin, the
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Tricircle local Neutron plugin(abbr: "local plugin") to trigger the cross
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OpenStack networking automation in local Neutron server. During virtual machine
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booting, local Nova server will interact with local Neutron server to query
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network or create port, which will trigger local plugin to retrieve data from
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central Neutron server and create necessary network resources according to the
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data. To support different core plugins, we will introduce a new option
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"real_core_plugin" in the "tricircle" configuration group. During
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initialization, local plugin will load the plugin specified by
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"real_core_plugin". Local plugin only adds logic to interact with central
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Neutron server, but invokes the real core plugin to finish the CRUD operations
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of local network resources. The following graph shows the relation between user
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and Nova and Neutron servers: ::
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+------+
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| user |
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+-+--+-+
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| |
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+-----------+ +----------------------+
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| boot vm create and query |
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| network resource |
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v |
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+----+-------+ |
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| local Nova | xxxxxxxxxxxxxxx |
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+----+-------+ xxx xxx |
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| xx xx |
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+---+ xxx +--------+ xxx |
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| x | | x |
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| x | | x |
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v V | v x v
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+--------+---------+ | +----+----------+----+
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| local Neutron | | | central Neutron |
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| +--------------+ | | | +----------------+ |
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| | local plugin | | | | | central plugin | |
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| +--------------+ | | | +----------------+ |
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+------------------+ | +--------------------+
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| |
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+-------------+
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Next using virtual machine booting procedure to elaborate how local plugin
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works. To begin with, user creates network and subnet via central Neutron
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server. Then this user passes the network id as the requested network
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information to local Nova server to boot a virtual machine. During parameter
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validation, local Nova server queries local Neutron server to ensure the
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passed-in network id is valid, which is a "network-get" request. In the
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"network-get" handle function, local plugin first checks if local Neutron
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already has a network with that id. If not, local plugin retrieves network and
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also subnet information from central Neutron server then creates network and
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subnet based on this information. User may pass an invalid network id by
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mistake, in this case, local plugin will receive a 404 response from central
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Neutron server, it just returns a 404 response to local Nova server.
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After the network id validation passes, local Nova server continues to schedule
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a host so compute manager running in that host will do the left works. Compute
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manager creates a port in the requested network via local Neutron server, which
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is a "port-create" request. In the "port-create" handle function, local plugin
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sends the same request to central Neutron server to create a port, and uses
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the returned port information to create a local port. With local plugin, we
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ensure all ip addresses are allocated by central Neutron server.
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At the end of the network setup of the virtual machine, compute manager issues
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a "port-update" request to local Neutron server to associate the host with the
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port. In the "port-update" handle function, local plugin recognizes that this
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request is sent from local Nova server by the request body that the request
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body contains host information, so it sends a "port-update" request to central
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Neutron server with region name in the request body. In Keystone, we register
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services inside one OpenStack instance as one unique region, so we can use
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region name to identify one OpenStack instance. After receiving the request,
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central Neutron server is informed that one virtual machine port is correctly
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setup in one OpenStack instance, so it starts the cross OpenStack networking
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automation process, like security group rule population, tunnel setup for
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layer2 communication and route setup for layer3 communication, which are done
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by making Neutron API call to each local Neutron server.
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Implementation
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==============
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Implementation details of the local plugin is discussed in this section.
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Resource Id
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-----------
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Local plugin always retrieves data of networks resources from central Neutron
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server and use these data to create network resources in local Neutron server.
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During the creation of these network resources, we need to guarantee resource
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ids in central and local server the same. Consider the scenario that user
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creates a port via central Neutron server then use this port to boot a virtual
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machine. After local Nova server receives the request, it will use the port id
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to create a tap device for the virtual machine. If port ids in central and
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local Neutron servers are different, OVS agent can't correctly recognize the
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tap device and configure it. As a result, virtual machine fails to connect to
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the network. Fortunately, database access module in Neutron allow us to specify
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id before creating the resource record, so in local plugin, we just specify id
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the same as central resource's to create local resource.
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Network Type Adaption
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---------------------
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Two network types are supported currently in central plugin, which are local
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and shared vlan type. Before creating network based on information retrieved
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from central Neutron server, local plugin needs to adapt network type. For
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local type, local plugin creates the network without specifying the network
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type, so the default tenant network type is used. For shared vlan type, local
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plugin changes the network type parameter from "shared_vlan" to "vlan", but
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keeps the segmentation id and physical network parameter.
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We plan to support another two network types later. They are shared_vxlan and
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mixed network type. For shared_vxlan type, local plugin changes the network
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type parameter from "shared_vxlan" to "vxlan", but keeps the segmentation id
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parameter(vxlan type doesn't need physical network parameter). For mixed type,
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like local type, local plugin uses the default tenant network type to create
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the network, but it needs to do one more thing, that is to save the segment
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information in central Neutron server. Neutron has a extension which allows one
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network to carry multiple segments information[1], so segment information of
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each local network can all be saved in the central network.
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Dhcp Port Handle
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----------------
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After local subnet creation, local Neutron server will schedule one dhcp agent
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for that subnet, and dhcp agent will automatically create a dhcp port. The ip
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address of this dhcp port is not allocated by central Neutron server, so we may
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encounter ip address conflict. We need to address this problem to ensure all ip
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addresses are allocated by central Neutron server.
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Here is the approach. After central Neutron server receives subnet creation
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subnet, central plugin not only creates the requested subnet, but also create a
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port to pre-allocate an ip address for the dhcp port. So during creation of
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local subnet, local plugin will query central Neutron server to retrieve the
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data of the pre-created port and use its ip address to create a local dhcp
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port. The "device_id" of the dhcp port is set to "reserved_dhcp_port" so after
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one dhcp agent is scheduled, it will use this port other than create a new one.
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Gateway Port Handle
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-------------------
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If cross OpenStack layer2 networking is enabled in one network, we need to
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allocate one gateway ip for that network in each OpenStack instance. The reason
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is that we want layer3 routing to be finished locally in each OpenStack
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instance. If all the OpenStack instances have the same gateway ip, packets sent
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to the gateway may reach the remote one, so the path is not the best and not
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predictable.
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How we address this problem in local plugin is that before creating local
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subnet, local plugin sends request to central Neutron server to create an
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"gateway port", then uses the ip of this port as the gateway ip of the local
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subnet. Name of the gateway port includes the region name of the OpenStack
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instance and the id of the subnet so each OpenStack instance can have its own
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gateway port and gateway ip for one specific subnet.
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Data Model Impact
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=================
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None
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Dependencies
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============
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None
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Documentation Impact
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====================
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Installation guide needs to be updated to introduce the configuration of
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central and local plugin.
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References
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==========
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[1] https://blueprints.launchpad.net/neutron/+spec/ml2-multi-segment-api
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