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-*- outline -*-
* Work out database for clustering or HA properly.
* Compromised chassis mitigation.
Possibly depends on database solution.
Latest discussion:
http://openvswitch.org/pipermail/dev/2016-August/078106.html
* Get incremental updates in ovn-controller and ovn-northd in some
sensible way.
* Testing improvements, possibly heavily based on ovn-trace.
Justin Pettit: "I'm planning to write some ovn-trace tests for IPv6.
Hopefully we can get those into 2.6."
* Self-managing HA for ovn-northd (avoiding the need to set up
independent tooling for fail-over).
Russell Bryant: "For bonus points, increasing N would scale out
ovn-northd if it was under too much load, but that's a secondary
concern."
* Live migration.
Russell Bryant: "When you're ready to have the destination take
over, you have to remove the iface-id from the source and add it at
the destination and i think it'd typically be configured on both
ends, since it's a clone of the source VM (and it's config)."
* VLAN trunk ports.
Russell Bryant: "Today that would require creating 4096 ports for
the VM and attach to 4096 OVN networks, so doable, but not quite
ideal."
* Native DNS support
Russell Bryant: "This is an OpenStack requirement to fully eliminate
the DHCP agent."
* Service function chaining.
* MAC learning.
Han Zhou: "To support VMs that hosts workloads with their own macs,
e.g. containers, if not using OVN native container support."
* Finish up ARP/ND support: re-checking bindings, expiring bindings.
* Hitless upgrade, especially for data plane.
* Use OpenFlow "bundles" for transactional data plane updates.
* L3 support
** Logical routers should send RST replies to TCP packets.
** IPv6 router ports should periodically send ND Router Advertisements.
* Dynamic IP to MAC binding enhancements.
OVN has basic support for establishing IP to MAC bindings dynamically,
using ARP.
** Ratelimiting.
From casual observation, Linux appears to generate at most one ARP per
second per destination.
This might be supported by adding a new OVN logical action for
rate-limiting.
** Tracking queries
It's probably best to only record in the database responses to queries
actually issued by an L3 logical router, so somehow they have to be
tracked, probably by putting a tentative binding without a MAC address
into the database.
** Renewal and expiration.
Something needs to make sure that bindings remain valid and expire
those that become stale.
One way to do this might be to add some support for time to the
database server itself.
** Table size limiting.
The table of MAC bindings must not be allowed to grow unreasonably
large.
** MTU handling (fragmentation on output)
* Security
** Limiting the impact of a compromised chassis.
Every instance of ovn-controller has the same full access to the central
OVN_Southbound database. This means that a compromised chassis can
interfere with the normal operation of the rest of the deployment. Some
specific examples include writing to the logical flow table to alter
traffic handling or updating the port binding table to claim ports that are
actually present on a different chassis. In practice, the compromised host
would be fighting against ovn-northd and other instances of ovn-controller
that would be trying to restore the correct state. The impact could include
at least temporarily redirecting traffic (so the compromised host could
receive traffic that it shouldn't) and potentially a more general denial of
service.
There are different potential improvements to this area. The first would be
to add some sort of ACL scheme to ovsdb-server. A proposal for this should
first include an ACL scheme for ovn-controller. An example policy would
be to make Logical_Flow read-only. Table-level control is needed, but is
not enough. For example, ovn-controller must be able to update the Chassis
and Encap tables, but should only be able to modify the rows associated with
that chassis and no others.
A more complex example is the Port_Binding table. Currently, ovn-controller
is the source of truth of where a port is located. There seems to be no
policy that can prevent malicious behavior of a compromised host with this
table.
An alternative scheme for port bindings would be to provide an optional mode
where an external entity controls port bindings and make them read-only to
ovn-controller. This is actually how OpenStack works today, for example.
The part of OpenStack that manages VMs (Nova) tells the networking component
(Neutron) where a port will be located, as opposed to the networking
component discovering it.
* ovsdb-server
ovsdb-server should have adequate features for OVN but it probably
needs work for scale and possibly for availability as deployments
grow. Here are some thoughts.
** Multithreading.
If it turns out that other changes don't let ovsdb-server scale
adequately, we can multithread ovsdb-server. Initially one might
only break protocol handling into separate threads, leaving the
actual database work serialized through a lock.
** Increasing availability.
Database availability might become an issue. The OVN system
shouldn't grind to a halt if the database becomes unavailable, but
it would become impossible to bring VIFs up or down, etc.
My current thought on how to increase availability is to add
clustering to ovsdb-server, probably via the Raft consensus
algorithm. As an experiment, I wrote an implementation of Raft
for Open vSwitch that you can clone from:
https://github.com/blp/ovs-reviews.git raft
** Reducing startup time.
As-is, if ovsdb-server restarts, every client will fetch a fresh
copy of the part of the database that it cares about. With
hundreds of clients, this could cause heavy CPU load on
ovsdb-server and use excessive network bandwidth. It would be
better to allow incremental updates even across connection loss.
One way might be to use "Difference Digests" as described in
Epstein et al., "What's the Difference? Efficient Set
Reconciliation Without Prior Context". (I'm not yet aware of
previous non-academic use of this technique.)
** Support multiple tunnel encapsulations in Chassis.
So far, both ovn-controller and ovn-controller-vtep only allow
chassis to have one tunnel encapsulation entry. We should extend
the implementation to support multiple tunnel encapsulations.
** Update learned MAC addresses from VTEP to OVN
The VTEP gateway stores all MAC addresses learned from its
physical interfaces in the 'Ucast_Macs_Local' and the
'Mcast_Macs_Local' tables. ovn-controller-vtep should be
able to update that information back to ovn-sb database,
so that other chassis know where to send packets destined
to the extended external network instead of broadcasting.
** Translate ovn-sb Multicast_Group table into VTEP config
The ovn-controller-vtep daemon should be able to translate
the Multicast_Group table entry in ovn-sb database into
Mcast_Macs_Remote table configuration in VTEP database.
* Consider the use of BFD as tunnel monitor.
The use of BFD for hypervisor-to-hypervisor tunnels is probably not worth it,
since there's no alternative to switch to if a tunnel goes down. It could
make sense at a slow rate if someone does OVN monitoring system integration,
but not otherwise.
When OVN gets to supporting HA for gateways (see ovn/OVN-GW-HA.md), BFD is
likely needed as a part of that solution.
There's more commentary in this ML post:
http://openvswitch.org/pipermail/dev/2015-November/062385.html
* ACL
** Support FTP ALGs.
** Support reject action.
** Support log option.
|
