This is adapted from a talk I gave at OpenStack Summit Sydney on Nov. 6. Signed-off-by: Ben Pfaff <b...@ovn.org> --- Documentation/automake.mk | 1 + Documentation/topics/index.rst | 1 + Documentation/topics/ovn-news-2.8.rst | 377 ++++++++++++++++++++++++++++++++++ 3 files changed, 379 insertions(+) create mode 100644 Documentation/topics/ovn-news-2.8.rst
diff --git a/Documentation/automake.mk b/Documentation/automake.mk index 733da3ca9da1..3ea2c2cb5fe0 100644 --- a/Documentation/automake.mk +++ b/Documentation/automake.mk @@ -40,6 +40,7 @@ DOC_SOURCE = \ Documentation/topics/integration.rst \ Documentation/topics/language-bindings.rst \ Documentation/topics/openflow.rst \ + Documentation/topics/ovn-news-2.8.rst \ Documentation/topics/ovsdb-replication.rst \ Documentation/topics/porting.rst \ Documentation/topics/role-based-access-control.rst \ diff --git a/Documentation/topics/index.rst b/Documentation/topics/index.rst index 00d6b0b837ec..13b6d8abbb30 100644 --- a/Documentation/topics/index.rst +++ b/Documentation/topics/index.rst @@ -58,6 +58,7 @@ OVN high-availability role-based-access-control + ovn-news-2.8 .. list-table:: diff --git a/Documentation/topics/ovn-news-2.8.rst b/Documentation/topics/ovn-news-2.8.rst new file mode 100644 index 000000000000..a6bac4bcdc13 --- /dev/null +++ b/Documentation/topics/ovn-news-2.8.rst @@ -0,0 +1,377 @@ +.. + Licensed under the Apache License, Version 2.0 (the "License"); you may + not use this file except in compliance with the License. You may obtain + a copy of the License at + + http://www.apache.org/licenses/LICENSE-2.0 + + Unless required by applicable law or agreed to in writing, software + distributed under the License is distributed on an "AS IS" BASIS, WITHOUT + WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. See the + License for the specific language governing permissions and limitations + under the License. + + Convention for heading levels in Open vSwitch documentation: + + ======= Heading 0 (reserved for the title in a document) + ------- Heading 1 + ~~~~~~~ Heading 2 + +++++++ Heading 3 + ''''''' Heading 4 + + Avoid deeper levels because they do not render well. + +=============================== +What's New with OVS and OVN 2.8 +=============================== + +This document is about what was added in Open vSwitch 2.8, which was released +at the end of August 2017, concentrating on the new features in OVN. It also +covers some of what is coming up in Open vSwitch and OVN 2.9, which is due to +be released in February 2018. OVN has many features, and this document does +not cover every new or enhanced feature (but contributions are welcome). + +Overview of OVN +--------------- + +Most readers probably know already about the general structure and purpose of +OVN, but it still seems wise to begin with a summary. OVN, the Open Virtual +Network project, is a sub-project of Open vSwitch that aims to implement a +general-purpose network virtualization system layered on top of Open vSwitch. +OVN is cloud management system independent, although it is most closely +integrated with OpenStack Neutron and Kubernetes. + +The architecture of OVN looks like this:: + + CMS + | + | + +-----------|-----------+ + | | | + | OVN/CMS Plugin | + | | | + | | | + | OVN Northbound DB | + | | | + | | | + | ovn-northd | + | | | + +-----------|-----------+ + | + | + +-------------------+ + | OVN Southbound DB | + +-------------------+ + | + | + +------------------+------------------+ + | | | + HV 1 | | HV n | + +---------------|---------------+ . +---------------|---------------+ + | | | . | | | + | ovn-controller | . | ovn-controller | + | | | | . | | | | + | | | | | | | | + | ovs-vswitchd ovsdb-server | | ovs-vswitchd ovsdb-server | + | | | | + +-------------------------------+ +-------------------------------+ + + +From the highest to lowest level, these layers and the software components that +connect them are: + +* The CMS, such as OpenStack Neutron. As the top level in the system, this is + the authoritative source of the virtual network configuration. + +* A CMS component specific to OVN, to translate the CMS's own configuration + into the format understood by OVN. In Neutron, this is ``networking-ovn``, + the driver that interfaces with OVN and translates the internal Neutron + representation of the virtual network into OVN's representation and pushes + that representation down the OVN northbound database. + +* The OVN Northbound database, aka NB DB. This is an instance of OVSDB, a + simple general-purpose database that is used for multiple purposes in Open + vSwitch and OVN. The NB DB's schema is in terms of networking concepts such + as switches and routers. The NB DB serves the purpose that in other systems + might be filled by some kind of API; for example, in place of calling an API + to create or delete a logical switch, ``networking-ovn`` performs these + operations by inserting or deleting a row in the NB DB's Logical_Switch + table. + + OVN's ``ovn-nbctl`` utility manipulates the northbound database. + +* The ``ovn-northd`` daemon, a program that runs centrally and translates the + NB DB's network representation into the lower-level representation used by + the OVN Southbound database in the next layer. The details of this daemon + are usually not of interest, although without it OVN will not work, so this + tutorial does not often mention it. + +* The OVN Southbound database, aka SB DB, which is also an OVSDB + database. Its schema is very different from the NB DB. Instead of + familiar networking concepts, the SB DB defines the network in terms + of collections of match-action rules called "logical flows", which + while similar in concept to OpenFlow flows use logical concepts, such + as virtual machine instances, in place of physical concepts like + physical Ethernet ports. + + OVN's ``ovn-sbctl`` utility can manipulate and observe the SB DB. + +* The ``ovn-controller`` daemon. A copy of ``ovn-controller`` runs on each + hypervisor. It reads logical flows from the SB DB, translates them into + OpenFlow flows, and sends them to Open vSwitch's ``ovs-vswitchd`` daemon. + Like ``ovn-northd``, usually the details of what this daemon are not of + interest, even though it's important to the operation of the system. + +* ``ovs-vswitchd``. This program runs on each hypervisor. It is the core of + Open vSwitch, which processes packets according to the OpenFlow flows set up + by ``ovn-controller``. + +* Open vSwitch datapath. This is essentially a cache designed to accelerate + packet processing. Open vSwitch includes a few different datapaths but OVN + installations typically use one based on the Open vSwitch Linux kernel + module. + +Debugging and Troubleshooting +----------------------------- + +Before version 2.8, Open vSwitch command-line tools were far more painful to +use than they needed to be. This section covers the improvements made to the +CLI in the 2.8 release. + +User-Hostile UUIDs +~~~~~~~~~~~~~~~~~~ + +The OVN CLI, through ``ovn-nbctl``, ``ovn-nbctl``, and ``ovn-trace``, used +full-length UUIDs almost everywhere. It didn't even provide any assistance +with completion, etc., which in practice meant always cutting and pasting UUIDs +from one command or window to another. This problem wasn't limited to the +places where one would expect to have to see or use a UUID, either. In many +places where one would expect to be able to use a network, router, or port +name, a UUID was required instead. In many places where one would want to see +a name, the UUID was displayed instead. More than anything else, these +shortcomings made the CLI user-hostile. + +There was an underlying problem that the southbound database didn't actually +contain all the information needed to provide a decent user interface. In some +cases, for example, the human-friendly names that one would want to use for +entities simply weren't part of the database. These names weren't necessary +for correctness, only for usability. + +OVN 2.8 eased many of these problems. Most parts of the CLI now allow the user +to abbreviate UUIDs, as long as the abbreviations are unique within the +database. Some parts of the CLI where full-length UUIDs make output hard to +read now abbreviate them themselves. Perhaps more importantly, in many places +the OVN CLI now displays and accepts human-friendly names for networks, +routers, ports, and other entities. In the places where the names were not +previously available, OVN (through ``ovn-northd``) now copies the names into +the southbound database. + +The CLIs for layers below OVN, at the OpenFlow and datapath layers with +``ovs-ofctl`` and ``ovs-dpctl``, respectively, had some similar problems in +which numbers were used for entities that had human-friendly names. Open +vSwitch 2.8 also solves some of those problems. Other than that, the most +notable enhancement in this area was the ``--no-stats`` option to ``ovs-ofctl +dump-flows``, which made that command's output more readable for the cases +where per-flow statistics were not interesting to the reader. + +Connections Between Levels +~~~~~~~~~~~~~~~~~~~~~~~~~~ + +OVN and Open vSwitch work almost like a stack of compilers: Neutron +configuration is translated to OVN northbound configuration, which the OVN +Neutron plugin translates to OVN southbound logical flows, which ``ovn-northd`` +translates to OpenFlow flows, which Open vSwitch translates to datapath flows. +For debugging and troubleshooting it is often necessary to understand exactly +how these translations work. The relationship from a logical flow to its +OpenFlow flows, or in the other direction, from an OpenFlow flow back to the +logical flow that produced it, was often of particular interest, but OVN didn't +provide good tools for the job. + +OVN 2.8 added some new features that ease these jobs. ``ovn-sbctl lflow-list`` +has a new option ``--ovs`` that lists the OpenFlow flows on a particular +chassis that were generated from the logical flows that it lists. +``ovn-trace`` also added a similar ``--ovs`` option that applies to the logical +flows it traces. + +In the other direction, OVN 2.8 added a new utility ``ovn-detrace`` that, given +an Open vSwitch trace of OpenFlow flows, annotates it with the logical flows +that yielded those OpenFlow flows. + +Distributed Firewall +~~~~~~~~~~~~~~~~~~~~ + +OVN supports a distributed firewall with stateful connection tracking to ensure +that only packets for established connections, or those that the configuration +explicitly allows, can ingress a given VM or container. Neutron uses this +feature by default. Most packets in an OpenStack environment pass through it +twice, once after egress from the packet's source VM and once before ingress +into its destination VM. Before OVN 2.8, the ``ovn-trace`` program, which +shows the path of a packet through an OVN logical network, did not support the +logical firewall, which in practice made it almost useless for Neutron. + +In OVN 2.8, ``ovn-trace`` adds support for the logical firewall. By default it +assumes that packets are part of an established connection, which is usually +what the user wants as part of the trace. It also accepts command-line options +to override that assumption, which allows the user to discover the treatment of +packets that the firewall should drop. + +At the next level deeper, prior to Open vSwitch 2.8, the OpenFlow tracing +command ``ofproto/trace`` also supported neither the connection tracking +feature underlying the OVN distributed firewall nor the "recirculation" feature +that accompanied it. This meant that, even if the user tried to look deeper +into the distributed firewall mechanism, he or she would encounter a further +roadblock. Open vSwitch 2.8 added support for both of these features as well. + +Summary Display +~~~~~~~~~~~~~~~ + +``ovn-nbctl show`` and ``ovn-sbctl show``, for showing an overview of the OVN +configuration, didn't show a lot of important information. OVN adds some more +useful information here. + +DNS, DHCP, and IPAM +------------------- + +OVN 2.8 adds a built-in DNS server designed for assigning names to VMs and +containers within an OVN logical network. DNS names are assigned using records +in the OVN northbound database and, like other OVN features, translated into +logical flows at the OVN southbound layer. DNS requests directed to the OVN +DNS server never leave the hypervisor from which the request is sent; instead, +OVN processes and replies to the request from its ``ovn-controller`` local +agent. The OVN DNS server is not a general-purpose DNS server and cannot be +used for that purpose. + +OVN has built-in support for DHCPv4 and DHCPv6. OVN 2.8 adds small +refinements. + +OVN includes simple built-in support for IP address management (IPAM), in which +OVN assigns IP addresses to VMs or containers from a pool or pools of IP +addresses delegated to it by the administrator. Before OVN 2.8, OVN IPAM only +supported IPv4 addresses; OVN 2.8 adds support for IPv6. OVN 2.8 also enhances +the address pool support to allow specific addresses to be excluded. Neutron +assigns IP addresses itself and does not use OVN IPAM. + +High Availability +----------------- + +As a distributed system, in OVN a lot can go wrong. As OVN advances, it adds +redundancy in places where currently a single failure could disrupt the +functioning of the system as a whole. OVN 2.8 adds two new kinds of high +availability. + +ovn-northd HA +~~~~~~~~~~~~~ + +The ``ovn-northd`` program sits between the OVN northbound and southbound +databases and translates from a logical network configuration into logical +flows. If ``ovn-northd`` itself or the host on which it runs fails, then +updates to the OVN northbound configuration will not propagate to the +hypervisors and the OVN configuration freezes in place until ``ovn-northd`` +restarts. + +OVN 2.8 adds support for active-backup HA to ``ovn-northd``. When more than +one ``ovn-northd`` instance runs, it uses an OVSDB locking feature to +automatically choose a single active instance. When that instance dies or +becomes nonresponsive, the OVSDB server automatically choose one of the +remaining instance(s) to take over. + +L3 Gateway HA +~~~~~~~~~~~~~ + +In OVN 2.8, multiple chassis may now be specified for L3 gateways. When more +than one chassis is specified, OVN manages high availability for that gateway. +Each hypervisor uses the BFD protocol to keep track of the gateway nodes that +are currently up. At any given time, a hypervisor uses the highest-priority +gateway node that is currently up. + +OVSDB +----- + +The OVN architecture relies heavily on OVSDB, the Open vSwitch database, for +hosting the northbound and southbound databases. OVSDB was originally selected +for this purpose because it was already used in Open vSwitch for configuring +OVS itself and, thus, it was well integrated with OVS and well supported in C +and Python, the two languages that are used in Open vSwitch. + +OVSDB was well designed for its original purpose of configuring Open vSwitch. +It supports ACID transactions, has a small, efficient server, a flexible schema +system, and good support for troubleshooting and debugging. However, it lacked +several features that are important for OVN but not for Open vSwitch. As OVN +advances, these missing features have become more and more of a problem. One +option would be to switch to a different database that already has many of +these features, but despite a careful search, no ideal existing database was +identified, so the project chose instead to improve OVSDB where necessary to +bring it up to speed. The following sections talk more about recent and future +improvements. + +High Availability +~~~~~~~~~~~~~~~~~ + +When ``ovsdb-server`` was only used for OVS configuration, high availability +was not important. ``ovsdb-server`` was capable of restarting itself +automatically if it crashed, and if the whole system went down then Open +vSwitch itself was dead too, so the database server's failure was not +important. + +In contrast, the northbound and southbound databases are centralized components +of a distributed system, so it is important that they not be a single point of +failure for the system as a whole. In released versions of OVN, +``ovsdb-server`` supports only "active-backup replication" across a pair of +servers. This means that if one server goes down, the other can pick it back +up approximately where the other one left off. The servers do not have +built-in support for deciding at any given time which is the active and which +the backup, so the administrator must configure an external agent to do this +management. + +Active-backup replication is not entirely satisfactory, for multiple reasons. +Replication is only approximate. Configuring the external agent requires extra +work. There is no benefit from the backup server except when the active server +fails. At most two servers can be used. + +A new form of high availability for OVSDB is under development for the OVN 2.9 +release, based on the Raft algorithm for distributed consensus. Whereas +replication uses two servers, clustering using Raft requires three or more +(typically an odd number) and continues functioning as long as more than half +of the servers are up. The clustering implementation is built into +``ovsdb-server`` and does not require an external agent. Clustering preserves +the ACID properties of the database, so that a transaction that commits is +guaranteed to persist. Finally, reads (which are the bulk of the OVN workload) +scale with the size of the cluster, so that adding more servers should improve +performance as the number of hypervisors in an OVN deployment increases. As of +this writing, OVSDB support for clustering is undergoing development and early +deployment testing. + +RBAC security +~~~~~~~~~~~~~ + +Until Open vSwitch 2.8, ``ovsdb-server`` had little support for access control +within a database. If an OVSDB client could modify the database at all, it +could make arbitrary changes. This was sufficient for most uses case to that +point. + +Hypervisors in an OVN deployment need access to the OVN southbound database. +Most of their access is reads, to find out about the OVN configuration. +Hypervisors do need some write access to the southbound database, primarily to +let the other hypervisors know what VMs and containers they are running and how +to reach them. Thus, OVN gives all of the hypervisors in the OVN deployment +write access to the OVN southbound database. This is fine when all is well, +but if any of the hypervisors were compromised then they could disrupt the +entire OVN deployment by corrupting the database. + +The OVN developers considered a few ways to solve this problem. One way would +be to introduce a new central service (perhaps in ``ovn-northd``) that provided +only the kinds of writes that the hypervisors legitimately need, and then grant +hypervisors direct access to the southbound database only for reads. But +ultimately the developers decided to introduce a new form of more access +control for OVSDB, called the OVSDB RBAC (role-based access control) feature. +OVSDB RBAC allows for granular enough control over access that hypervisors can +be granted only the ability to add, modify, and delete the records that relate +to themselves, preventing them from corrupting the database as a whole. + +Further Directions +------------------ + +For more information about new features in OVN and Open vSwitch, please refer +to the NEWS file distributed with the source tree. If you have questions about +Open vSwitch or OVN features, please feel free to write to the Open vSwitch +discussion mailing list at ovs-disc...@openvswitch.org. -- 2.10.2 _______________________________________________ dev mailing list d...@openvswitch.org https://mail.openvswitch.org/mailman/listinfo/ovs-dev