ovs/Documentation/ref/ovsdb-server.7.rst

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============
ovsdb-server
============

Description
===========

``ovsdb-server`` implements the Open vSwitch Database (OVSDB) protocol
specified in RFC 7047.  This document provides clarifications for how
``ovsdb-server`` implements the protocol and describes the extensions that it
provides beyond RFC 7047.  Numbers in section headings refer to corresponding
sections in RFC 7047.

3.1 JSON Usage
--------------

RFC 4627 says that names within a JSON object should be unique.
The Open vSwitch JSON parser discards all but the last value
for a name that is specified more than once.

The definition of <error> allows for implementation extensions.
Currently ``ovsdb-server`` uses the following additional ``error``
strings (which might change in later releases):

``syntax error`` or ``unknown column``
    The request could not be parsed as an OVSDB request.  An additional
    ``syntax`` member, whose value is a string that contains JSON, may narrow
    down the particular syntax that could not be parsed.

``internal error``
    The request triggered a bug in ``ovsdb-server``.

``ovsdb error``
    A map or set contains a duplicate key.

``permission error``
    The request was denied by the role-based access control extension,
    introduced in version 2.8.

3.2 Schema Format
-----------------

RFC 7047 requires the ``version`` field in <database-schema>.  Current versions
of ``ovsdb-server`` allow it to be omitted (future versions are likely to
require it).

RFC 7047 allows columns that contain weak references to be immutable.  This
raises the issue of the behavior of the weak reference when the rows that it
references are deleted.  Since version 2.6, ``ovsdb-server`` forces columns
that contain weak references to be mutable.

Since version 2.8, the table name ``RBAC_Role`` is used internally by the
role-based access control extension to ``ovsdb-server`` and should not be used
for purposes other than defining mappings of role names to table access
permissions. This table has one row per role name and the following columns:

``name``
    The role name.

``permissions``
    A map of table name to a reference to a row in a separate permission table.

The separate RBAC permission table has one row per access control
configuration and the following columns:

``name``
    The name of the table to which the row applies.

``authorization``
    The set of column names and column:key pairs to be compared with the client
    ID in order to determine the authorization status of the requested
    operation.

``insert_delete``
    A boolean value, true if authorized insertions and deletions are allowed,
    false if no insertions or deletions are allowed.

``update``
    The set of columns and column:key pairs for which authorized update and
    mutate operations should be permitted.

4 Wire Protocol
---------------

The original OVSDB specifications included the following reasons, omitted from
RFC 7047, to operate JSON-RPC directly over a stream instead of over HTTP:

* JSON-RPC is a peer-to-peer protocol, but HTTP is a client-server protocol,
  which is a poor match.  Thus, JSON-RPC over HTTP requires the client to
  periodically poll the server to receive server requests.

* HTTP is more complicated than stream connections and doesn't provide any
  corresponding advantage.

* The JSON-RPC specification for HTTP transport is incomplete.

4.1.3 Transact
--------------

Since version 2.8, role-based access controls can be applied to operations
within a transaction that would modify the contents of the database (these
operations include row insert, row delete, column update, and column
mutate). Role-based access controls are applied when the database schema
contains a table with the name ``RBAC_Role`` and the connection on which the
transaction request was received has an associated role name (from the ``role``
column in the remote connection table). When role-based access controls are
enabled, transactions that are otherwise well-formed may be rejected depending
on the client's role, ID, and the contents of the ``RBAC_Role`` table and
associated permissions table.

4.1.5 Monitor
-------------

For backward compatibility, ``ovsdb-server`` currently permits a single
<monitor-request> to be used instead of an array; it is treated as a
single-element array.  Future versions of ``ovsdb-server`` might remove this
compatibility feature.

Because the <json-value> parameter is used to match subsequent update
notifications (see below) to the request, it must be unique among all active
monitors.  ``ovsdb-server`` rejects attempt to create two monitors with the
same identifier.

4.1.7 Monitor Cancellation
--------------------------

When a database monitored by a session is removed, and database change
awareness is enabled for the session (see Section 4.1.16), the database server
spontaneously cancels all monitors (including conditional monitors described in
Section 4.1.12) for the removed database.  For each canceled monitor, it issues
a notification in the following form::

    "method": "monitor_canceled"
    "params": [<json-value>]
    "id": null

4.1.12 Monitor_cond
-------------------

A new monitor method added in Open vSwitch version 2.6.  The ``monitor_cond``
request enables a client to replicate subsets of tables within an OVSDB
database by requesting notifications of changes to rows matching one of the
conditions specified in ``where`` by receiving the specified contents of these
rows when table updates occur.  ``monitor_cond`` also allows a more efficient
update notifications by receiving <table-updates2> notifications (described
below).

The ``monitor`` method described in Section 4.1.5 also applies to
``monitor_cond``, with the following exceptions:

* RPC request method becomes ``monitor_cond``.

* Reply result follows <table-updates2>, described in Section 4.1.14.

* Subsequent changes are sent to the client using the ``update2`` monitor
  notification, described in Section 4.1.14

* Update notifications are being sent only for rows matching [<condition>*].


The request object has the following members::

    "method": "monitor_cond"
    "params": [<db-name>, <json-value>, <monitor-cond-requests>]
    "id": <nonnull-json-value>

The <json-value> parameter is used to match subsequent update notifications
(see below) to this request.  The <monitor-cond-requests> object maps the name
of the table to an array of <monitor-cond-request>.

Each <monitor-cond-request> is an object with the following members::

    "columns": [<column>*]            optional
    "where": [<condition>*]           optional
    "select": <monitor-select>        optional

The ``columns``, if present, define the columns within the table to be
monitored that match conditions.  If not present, all columns are monitored.

The ``where``, if present, is a JSON array of <condition> and boolean values.
If not present or condition is an empty array, implicit True will be considered
and updates on all rows will be sent.

<monitor-select> is an object with the following members::

    "initial": <boolean>              optional
    "insert": <boolean>               optional
    "delete": <boolean>               optional
    "modify": <boolean>               optional

The contents of this object specify how the columns or table are to be
monitored as explained in more detail below.

The response object has the following members::

    "result": <table-updates2>
    "error": null
    "id": same "id" as request

The <table-updates2> object is described in detail in Section 4.1.14.  It
contains the contents of the tables for which initial rows are selected.  If no
tables initial contents are requested, then ``result`` is an empty object.

Subsequently, when changes to a specified table that match one of the
conditions in <monitor-cond-request> are committed, the changes are
automatically sent to the client using the ``update2`` monitor notification
(see Section 4.1.14).  This monitoring persists until the JSON-RPC session
terminates or until the client sends a ``monitor_cancel`` JSON-RPC request.

Each <monitor-cond-request> specifies one or more conditions and the manner in
which the rows that match the conditions are to be monitored.  The
circumstances in which an ``update`` notification is sent for a row within the
table are determined by <monitor-select>:

* If ``initial`` is omitted or true, every row in the original table that
  matches one of the conditions is sent as part of the response to the
  ``monitor_cond`` request.

* If ``insert`` is omitted or true, update notifications are sent for rows
  newly inserted into the table that match conditions or for rows modified in
  the table so that their old version does not match the condition and new
  version does.

* If ``delete`` is omitted or true, update notifications are sent for rows
  deleted from the table that match conditions or for rows modified in the
  table so that their old version does match the conditions and new version
  does not.

* If ``modify`` is omitted or true, update notifications are sent whenever a
  row in the table that matches conditions in both old and new version is
  modified.

Both ``monitor`` and ``monitor_cond`` sessions can exist concurrently. However,
``monitor`` and ``monitor_cond`` shares the same <json-value> parameter space;
it must be unique among all ``monitor`` and ``monitor_cond`` sessions.

4.1.13 Monitor_cond_change
--------------------------

The ``monitor_cond_change`` request enables a client to change an existing
``monitor_cond`` replication of the database by specifying a new condition and
columns for each replicated table.  Currently changing the columns set is not
supported.

The request object has the following members::

    "method": "monitor_cond_change"
    "params": [<json-value>, <json-value>, <monitor-cond-update-requests>]
    "id": <nonnull-json-value>

The <json-value> parameter should have a value of an existing conditional
monitoring session from this client. The second <json-value> in params array is
the requested value for this session. This value is valid only after
``monitor_cond_change`` is committed. A user can use these values to
distinguish between update messages before conditions update and after. The
<monitor-cond-update-requests> object maps the name of the table to an array of
<monitor-cond-update-request>.  Monitored tables not included in
<monitor-cond-update-requests> retain their current conditions.

Each <monitor-cond-update-request> is an object with the following members::

    "columns": [<column>*]         optional
    "where": [<condition>*]        optional

The ``columns`` specify a new array of columns to be monitored, although this
feature is not yet supported.

The ``where`` specify a new array of conditions to be applied to this
monitoring session.

The response object has the following members::

    "result": null
    "error": null
    "id": same "id" as request

Subsequent <table-updates2> notifications are described in detail in Section
4.1.14 in the RFC.  If insert contents are requested by original monitor_cond
request, <table-updates2> will contain rows that match the new condition and do
not match the old condition.  If deleted contents are requested by origin
monitor request, <table-updates2> will contain any matched rows by old
condition and not matched by the new condition.

Changes according to the new conditions are automatically sent to the client
using the ``update2`` monitor notification.  An update, if any, as a result of
a condition change, will be sent to the client before the reply to the
``monitor_cond_change`` request.

4.1.14 Update2 notification
---------------------------

The ``update2`` notification is sent by the server to the client to report
changes in tables that are being monitored following a ``monitor_cond`` request
as described above. The notification has the following members::

    "method": "update2"
    "params": [<json-value>, <table-updates2>]
    "id": null

The <json-value> in ``params`` is the same as the value passed as the
<json-value> in ``params`` for the corresponding ``monitor`` request.
<table-updates2> is an object that maps from a table name to a <table-update2>.
A <table-update2> is an object that maps from row's UUID to a <row-update2>
object. A <row-update2> is an object with one of the following members:

``"initial": <row>``
    present for ``initial`` updates

``"insert": <row>``
    present for ``insert`` updates

``"delete": <row>``
    present for ``delete`` updates

``"modify": <row>"``
    present for ``modify`` updates

The format of <row> is described in Section 5.1.

<row> is always a null object for a ``delete`` update.  In ``initial`` and
``insert`` updates, <row> omits columns whose values equal the default value of
the column type.

For a ``modify`` update, <row> contains only the columns that are modified.
<row> stores the difference between the old and new value for those columns, as
described below.

For columns with single value, the difference is the value of the new column.

The difference between two sets are all elements that only belong to one of the
sets.

The difference between two maps are all key-value pairs whose keys appears in
only one of the maps, plus the key-value pairs whose keys appear in both maps
but with different values.  For the latter elements, <row> includes the value
from the new column.

Initial views of rows are not presented in update2 notifications, but in the
response object to the ``monitor_cond`` request.  The formatting of the
<table-updates2> object, however, is the same in either case.

4.1.15 Monitor_cond_since
-------------------------

A new monitor method added in Open vSwitch version 2.12.  The
``monitor_cond_since`` request enables a client to request changes that
happened after a specific transaction id. A client can use this feature to
request only latest changes after a server connection reset instead of
re-transfer all data from the server again.

The ``monitor_cond`` method described in Section 4.1.12 also applies to
``monitor_cond_since``, with the following exceptions:

* RPC request method becomes ``monitor_cond_since``.

* Reply result includes extra parameters.

* Subsequent changes are sent to the client using the ``update3`` monitor
  notification, described in Section 4.1.16

The request object has the following members::

    "method": "monitor_cond_since"
    "params": [<db-name>, <json-value>, <monitor-cond-requests>, <last-txn-id>]
    "id": <nonnull-json-value>

The <last-txn-id> parameter is the transaction id that identifies the latest
data the client already has, and it requests server to send changes AFTER this
transaction (exclusive).

All other parameters are the same as ``monitor_cond`` method.

The response object has the following members::

    "result": [<found>, <last-txn-id>, <table-updates2>]
    "error": null
    "id": same "id" as request

The <found> is a boolean value that tells if the <last-txn-id> requested by
client is found in server's history or not. If true, the changes after that
version up to current is sent. Otherwise, all data is sent.

The <last-txn-id> is the transaction id that identifies the latest transaction
included in the changes in <table-updates2> of this response, so that client
can keep tracking.  If there is no change involved in this response, it is the
same as the <last-txn-id> in the request if <found> is true, or zero uuid if
<found> is false.  If the server does not support transaction uuid, it will
be zero uuid as well.

All other parameters are the same as in response object of ``monitor_cond``
method.

Like in ``monitor_cond``, subsequent changes that match conditions in
<monitor-cond-request> are automatically sent to the client, but using
``update3`` monitor notification (see Section 4.1.16), instead of ``update2``.

4.1.16 Update3 notification
---------------------------

The ``update3`` notification is sent by the server to the client to report
changes in tables that are being monitored following a ``monitor_cond_since``
request as described above. The notification has the following members::

    "method": "update3"
    "params": [<json-value>, <last-txn-id>, <table-updates2>]
    "id": null

The <last-txn-id> is the same as described in the response object of
``monitor_cond_since``.

All other parameters are the same as in ``update2`` monitor notification (see
Section 4.1.14).

4.1.17 Get Server ID
--------------------

A new RPC method added in Open vSwitch version 2.7.  The request contains the
following members::

    "method": "get_server_id"
    "params": null
    "id": <nonnull-json-value>

The response object contains the following members::

    "result": "<server_id>"
    "error": null
    "id": same "id" as request

<server_id> is JSON string that contains a UUID that uniquely identifies the
running OVSDB server process.  A fresh UUID is generated when the process
restarts.

4.1.18 Database Change Awareness
--------------------------------

RFC 7047 does not provide a way for a client to find out about some kinds of
configuration changes, such as about databases added or removed while a client
is connected to the server, or databases changing between read/write and
read-only due to a transition between active and backup roles.  Traditionally,
``ovsdb-server`` disconnects all of its clients when this happens, because this
prompts a well-written client to reassess what is available from the server
when it reconnects.

OVS 2.9 provides a way for clients to keep track of these kinds of changes, by
monitoring the ``Database`` table in the ``_Server`` database introduced in
this release (see ``ovsdb-server(5)`` for details).  By itself, this does not
suppress ``ovsdb-server`` disconnection behavior, because a client might
monitor this database without understanding its special semantics.  Instead,
``ovsdb-server`` provides a special request::

    "method": "set_db_change_aware"
    "params": [<boolean>]
    "id": <nonnull-json-value>

If the boolean in the request is true, it suppresses the connection-closing
behavior for the current connection, and false restores the default behavior.
The reply is always the same::

    "result": {}
    "error": null
    "id": same "id" as request

4.1.19 Schema Conversion
------------------------

Open vSwitch 2.9 adds a new JSON-RPC request to convert an online database from
one schema to another.  The request contains the following members::

    "method": "convert"
    "params": [<db-name>, <database-schema>]
    "id": <nonnull-json-value>

Upon receipt, the server converts database <db-name> to schema
<database-schema>.  The schema's name must be <db-name>.  The conversion is
atomic, consistent, isolated, and durable.  The data in the database must be
valid when interpreted under <database-schema>, with only one exception: data
for tables and columns that do not exist in the new schema are ignored.
Columns that exist in <database-schema> but not in the database are set to
their default values.  All of the new schema's constraints apply in full.

If the conversion is successful, the server notifies clients that use the
``set_db_change_aware`` RPC introduced in Open vSwitch 2.9 and cancels their
outstanding transactions and monitors.  The server disconnects other clients,
enabling them to notice the change when they reconnect.  The server sends the
following reply::

    "result": {}
    "error": null
    "id": same "id" as request

If the conversion fails, then the server sends an error reply in the following
form::

    "result": null
    "error": [<error>]
    "id": same "id" as request

5.1 Notation
------------

For <condition>, RFC 7047 only allows the use of ``!=``, ``==``, ``includes``,
and ``excludes`` operators with set types.  Open vSwitch 2.4 and later extend
<condition> to allow the use of ``<``, ``<=``, ``>=``, and ``>`` operators with
a column with type "set of 0 or 1 integer" and an integer argument, and with
"set of 0 or 1 real" and a real argument.  These conditions evaluate to false
when the column is empty, and otherwise as described in RFC 7047 for integer
and real types.

<condition> is specified in Section 5.1 in the RFC with the following change: A
condition can be either a 3-element JSON array as described in the RFC or a
boolean value. In case of an empty array an implicit true boolean value will be
considered.

5.2.6 Wait, 5.2.7 Commit, 5.2.9 Comment
---------------------------------------

RFC 7047 says that the ``wait``, ``commit``, and ``comment`` operations have no
corresponding result object.  This is not true.  Instead, when such an
operation is successful, it yields a result object with no members.