RETIRED, Tricircle is to provide networking automation across Neutron.
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tricircle/doc/source/devspecs/lbaas.rst

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Distributed LBaaS in Multi-Region Scenario

Background

Currently, LBaaS (Load-Balancing-as-a-Service) is not supported in the Tricircle. This spec is to describe how LBaaS will be implemented in the Tricircle. LBaaS is an advanced service of Neutron, which allows for proprietary and open-source load balancing technologies to drive the actual load balancing of requests. Based on the networking guide of Ocata release, LBaaS can be configured with an agent or Octavia. Given that the OpenStack community try to take Octavia as the reference implementation of LBaaS, we only enable LBaaS based on Octavia in the Tricircle.

Different from existing LBaaS implementation, Octavia accomplishes its delivery of load balancing services by managing a fleet of virtual machines, containers, or bare metal servers, collectively known as amphorae, which it spins up on demand. This spec file is dedicated to how to implement LBaaS in multiple regions with the Tricircle.

Overall Implementation

The Tricircle is designed in a central-local fashion, where all the local neutrons are managed by the central neutron. As a result, in order to adapt the central-local design and the amphorae mechanism of Octavia, we plan to deploy LBaaS as follows. :

+---------------------------+
|                           |
|      Central Neutron      |
|                           |
+---------------------------+
       Central Region

+----------------------------+    +-----------------------------+
|     +----------------+     |    |     +----------------+      |
|     |  LBaaS Octavia |     |    |     |  LBaaS Octavia |      |
|     +----------------+     |    |     +----------------+      |
| +------+ +---------------+ |    | +-------+ +---------------+ |
| | Nova | | Local Neutron | |    | | Nova  | | Local Neutron | |
| +------+ +---------------+ |    | +-------+ +---------------+ |
+----------------------------+    +-----------------------------+
Region One                          Region Two

As demonstrated in the figure above, for each region where a local neutron is installed, admins can optionally choose to configure and install Octavia. Typically, Octavia leverages nova installed in its region to spin up amphorae. By employing load balancing softwares (e.g. haproxy) installed in the amphorae and Virtual Router Redundancy Protocol (VRRP), a load balancer which consists of a VIP and an amphora, can balance load across members with high availability. However, under the central-local scenario, we plan to let Octavia employ the central neutron in Central Region to manage networking resources, while still employ services in its region to manage amphora. Hence, the workflow of networking resource management in Tricircle can be described as follows.

Tenant-->local neutron API-->neutron-LBaaS--->local Octavia--->central neutron

Specifically, when a tenant attempts to create a load balancer, he/she needs to send a request to the local neutron-lbaas service. The service plugin of neutron-lbaas then prepares for creating the load balancer, including creating port via local plugin, inserting the info of the port into the database, and so on. Next the service plugin triggers the creating function of the corresponding driver of Octavia, i.e., Octavia.network.drivers.neutron.AllowedAddressPairsDriver to create the amphora. During the creation, Octavia employs the central neutron to complete a series of operations, for instance, allocating VIP, plugging in VIP, updating databases. Given that the main features of managing networking resource are implemented, we hence need to adapt the mechanism of Octavia and neutron-lbaas by improving the functionalities of the local and central plugins.

Considering the Tricircle is dedicated to enabling networking automation across Neutrons, the implementation can be divided as two parts, i.e., LBaaS members in one OpenStack instance, and LBaaS members in multiple OpenStack instances.

LBaaS members in single region

For LBaaS in one region, after installing octavia, cloud tenants should build a management network and two security groups for amphorae manually in the central neutron. Next, tenants need to create an interface for health management. Then, tenants need to configure the newly created networking resources for octavia and let octavia employ central neutron to create resources. Finally, tenants can create load balancers, listeners, pools, and members in the local neutron. In this case, all the members of a loadbalancer are in one region, regardless of whether the members reside in the same subnet or not.

LBaaS members in multiple regions

1. members in the same subnet yet locating in different regions

As shown below. :

+-------------------------------+  +-----------------------+
| +---------------------------+ |  |                       |
| |    Amphora                | |  |                       |
| |                           | |  |                       |
| |  +-------+  +---------+   | |  |                       |
| +--+ mgmt  +--+ subnet1 +---+ |  |                       |
|    +-------+  +---------+     |  |                       |
|                               |  |                       |
| +--------------------------+  |  | +-------------------+ |
| | +---------+  +---------+ |  |  | |    +---------+    | |
| | | member1 |  | member2 | |  |  | |    | member3 |    | |
| | +---------+  +---------+ |  |  | |    +---------+    | |
| +--------------------------+  |  | +-------------------+ |
|       network1(subnet1)       |  |   network1(subnet1)   |
+-------------------------------+  +-----------------------+
           Region One                     Region Two
Fig. 1. The scenario of balancing load across instances of one subnet which
reside in different regions.

As shown in Fig. 1, suppose that a load balancer is created in Region one, and hence a listener, a pool, and two members in subnet1. When adding an instance in Region Two to the pool as a member, the local neutron creates the network in Region Two. Members that locate in different regions yet reside in the same subnet form a shared VLAN/VxLAN network. As a result, the Tricircle supports adding members that locates in different regions to a pool.

2. members residing in different subnets and regions

As shown below. :

+---------------------------------------+  +-----------------------+
| +-----------------------------------+ |  |                       |
| |            Amphora                | |  |                       |
| |                                   | |  |                       |
| | +---------+  +------+ +---------+ | |  |                       |
| +-+ subnet2 +--+ mgmt +-+ subnet1 +-+ |  |                       |
|   +---------+  +------+ +---------+   |  |                       |
|                                       |  |                       |
| +----------------------------------+  |  | +-------------------+ |
| |                                  |  |  | |                   | |
| |   +---------+      +---------+   |  |  | |    +---------+    | |
| |   | member1 |      | member2 |   |  |  | |    | member3 |    | |
| |   +---------+      +---------+   |  |  | |    +---------+    | |
| |                                  |  |  | |                   | |
| +----------------------------------+  |  | +-------------------+ |
|           network1(subnet1)           |  |    network2(subnet2)  |
+---------------------------------------+  +-----------------------+
               Region One                         Region Two
Fig. 2. The scenario of balancing load across instances of different subnets
which reside in different regions as well.

As show in Fig. 2, supposing that a load balancer is created in region one, as well as a listener, a pool, and two members in subnet1. When adding an instance of subnet2 located in region two, the local neutron-lbaas queries the central neutron whether subnet2 exist or not. If subnet2 exists, the local neutron-lbaas employ octavia to plug a port of subnet2 to the amphora. This triggers cross-region vxlan networking process, then the amphora can reach the members. As a result, the LBaaS in multiple regions works.

Please note that LBaaS in multiple regions should not be applied to the local network case. When adding a member in a local network which resides in other regions, neutron-lbaas use 'get_subnet' will fail and returns "network not located in current region"

Data Model Impact

None

Dependencies

None

Documentation Impact

Configuration guide needs to be updated to introduce the configuration of Octavia, local neutron, and central neutron.

References

None