[openstack-dev] [octavia] enabling new topologies
GUENEN at il.ibm.com
Sun May 29 14:12:23 UTC 2016
I'm working with the IBM team implementing the Active-Active N+1 topology
I've been commissioned with the task to help integrate the code supporting
the new topology while a) making as few code changes and b) reusing as
much code as possible.
To make sure the changes to existing code are future-proof, I'd like to
implement them outside AA N+1, submit them on their own and let the AA N+1
base itself on top of it.
what follows is a description of the challenges I'm facing and the way I
propose to solve them. Please skip down to the end of the email to see the
I've been studying the code for a few weeks now to see where the best
places for minimal changes might be.
Currently I see two options:
1. introduce a new kind of entity (the distributor) and make sure it's
being handled on any of the 6 levels of controller worker code (endpoint,
controller worker, *_flows, *_tasks, *_driver)
2. leave most of the code layers intact by building on the fact that
distributor will inherit most of the controller worker logic of amphora
In Active-Active topology, very much like in Active/StandBy:
* top level of distributors will have to run VRRP
* the distributors will have a Neutron port made on the VIP network
* the distributors' neutron ports on VIP network will need the same
* the amphorae facing the pool member networks still require
* ports on the pool member networks
* "peers" HAProxy configuration for real-time state exchange
* VIP network connections with the right security groups
The fact that existing topologies lack the notion of distributor and
inspecting the 30-or-so existing references to amphorae clusters, swayed
me towards the second option.
The easiest way to make use of existing code seems to be by splitting
load-balancer's amphorae into three overlapping sets:
1. The front-facing - those connected to the VIP network
2. The back-facing - subset of front-facing amphorae, also connected to
the pool members' networks
3. The VRRP-running - subset of front-facing amphorae, making sure the VIP
routing remains highly available
At the code-changes level
* the three sets can be simply added as properties of
* the existing amphorae cluster references would switch to using one of
these properties, for example
* the VRRP sub-flow would loop over only the VRRP amphorae
* the network driver, when plugging the VIP, would loop over the
* when connecting to the pool members' networks,
network_tasks.CalculateDelta would only loop over the back-facing amphorae
In terms of backwards compatibility, Active-StandBy topology would have
the 3 sets equal and contain both of its amphorae.
An even more future-proof approach might be to implement the sets-getters
as selector methods, supporting operation on subsets of each kind of
amphorae. For instance when growing/shrinking back-facing amphorae
cluster, only the added/removed ones will need to be processed.
Finally (thank you for your patience, dear reader), my question is: if any
of the above makes sense, and to facilitate the design/code review, what
would be the best way to move forward?
Should I create a mini-blueprint describing the changes and implement it?
Should I just open a bug for it and supply a fix?
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