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Adam Osuchowski
Kea
Commits
cb8fec27
Commit
cb8fec27
authored
Aug 09, 2017
by
Thomas Markwalder
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[5280] A bit of wordsmithing on lease_cmds.dox
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src/hooks/dhcp/lease_cmds/lease_cmds.dox
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src/hooks/dhcp/lease_cmds/lease_cmds.dox
View file @
cb8fec27
...
...
@@ -8,8 +8,8 @@
@mainpage Kea Lease Commands Hooks Library
Welcome to Kea Lease Commands Hooks Library. This documentation is addressed
a
t
developers who are interested in internal operation of the Lease Commands
Welcome to Kea Lease Commands Hooks Library. This documentation is addressed t
o
developers who are interested in
the
internal operation of the Lease Commands
library. This file provides information needed to understand and perhaps extend
this library.
...
...
@@ -29,22 +29,21 @@ command is issued (be it directly via control channel or indirectly via REST
interface from control agent), the code receives a JSON command with
parameters. Those are parsed and then actual operation commences. This
operation always interacts with an instantiation of isc::dhcp::LeaseMgr
instance, which is Kea's way of storing leases. At time of writing this text
instance, which is Kea's way of storing leases. At
the
time of writing this text
(Aug. 2017), Kea supports four types of lease managers: memfile, MySQL,
PostgreSQL or Cassandra. Th
o
se commands provide
a unified interface for those
backends.
PostgreSQL or Cassandra. Th
e lea
se commands provide
d by this library
provide a unified interface for those
backends.
As with other hooks,
also
this one keeps its code in separate namespace
,
which
As with other hooks, this one
also
keeps its code in
a
separate namespace which
corresponds to the file name of the library: isc::lease_cmds.
@section lease_cmdsCode Lease Commands Code Overview
The library operation starts with Kea calling load() function (file
load_unload.cc). It instantiates isc::lease_cmds::LeaseCmds object. Constructor
of that object registers all commands. For a list, see @ref
isc::lease_cmds::LeaseCmds class documentation. This class uses Pimpl design
pattern, thus the real implementation is hidden in
isc::lease_cmds::LeaseCmdsImpl.
The library operation starts with Kea calling the load() function (file
load_unload.cc). It instantiates an isc::lease_cmds::LeaseCmds object.
The constructor of that object registers all of the lease commands. For a list,
see @ref isc::lease_cmds::LeaseCmds class documentation. This class uses Pimpl
design pattern, thus the real implementation is hidden in isc::lease_cmds::LeaseCmdsImpl.
Almost every command has its own handler, except few that share the same handler
between v4 and v6 due to its similarity. For example
...
...
@@ -69,29 +68,29 @@ For details see documentation and code of the following handlers:
@section lease_cmdsDesigns Lease Commands Design choices
The lease manipulation commands were implemented to provide convenient interface
The lease manipulation commands were implemented to provide
a
convenient interface
for sysadmins. The primary goal was to offer a way to interact with the live
lease database in unified way, regardless of the actual backend being used.
For some backends (MySQL, PostgreSQL and Cassandra) it is possible to interact
with the backend while Kea is running and possibly change its content. This
is both powerful and dangerous
ability
. In particular, only rudimentary
directly
with the backend while Kea is running and possibly change its content. This
ability
is both powerful and dangerous. In particular, only rudimentary
checks are enforced by the DB schemas (e.g. not possible to have two leases
for the same address). However, it does not prevent sysadmins from making
more obscure errors, like inserting leases for subnets that do not exist
or configing an address that is topologically outside of the subnet
it was
supposed to
belong
to
. Th
is
kind of checks
is
only possible by DHCP-aware
or config
ur
ing an address that is topologically outside of the subnet
to which
it should
belong. Th
ese
kind of checks
are
only possible by DHCP-aware
code, which this library provides.
Some of the queries may require a seemingly odd set of parameters. For example,
lease6-get query requires at least
duid
, subnet-id and
iaid
to retrieve a lease
by DUID. The need for a sysadmin to know and specify an
iaid
is troublesome.
lease6-get query requires at least
DUID
, subnet-id and
IAID
to retrieve a lease
by DUID. The need for a sysadmin to know and specify an
IAID
is troublesome.
However, the guiding principle here was to use whatever queries were already
exposed by lease manager and not introduce new indexes, unless absolutely
exposed by
the
lease manager and not introduce new indexes, unless absolutely
necessary. This ensures that there is no performance degradation when the
library is loaded. The only exception for that was lease4-wipe and lease6-wipe
commands that remove all leases from specifi
e
c subnet. As there were no
queries that could retrieve or otherwise enumerate leases f
rom
specific subnet,
a new query type
(
and a new index
)
had to be
develop
ed.
commands that remove all leases from specific subnet. As there were no
queries that could retrieve or otherwise enumerate leases f
or a
specific subnet,
a new query type and a new index had to be
add
ed.
*/
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