Module 9: CDB Technical Intro

1©2015 Tail-f Systems all rights reserved February 13, 2015

CDB Technical Introduction


CDB – ConfD Database

NETCONF SNMP REST CLI Web

CDBDatabase

Data Provider API

CDB API

Management Agent API

App AppApp

ConfD Core Engine

App

External DatabaseOperational

Data

App

• Hierarchical database

• ACID test compliant

• Atomicity, consistency, isolation, durability

• Fast, lightweight, fault-tolerant

• Compact binary XML format

• Memory resident with journal in persistent storage

• Schema automatically derived from YANG

• Supports 1:N data replication

• Supports automatic schema version up/downgrades

• CDB can hold some or all data

• Configuration data and/or Operational data

• External database can be used in addition to or instead of

• Automatic loading of initial data

• Applications read data, then subscribe to relevant configuration changes

• Subscription notifications with priority level ordering

• Multiple datastores per NETCONF standards

• Startup, running, candidate, operational


Hierarchical

• CDB uses an Hierarchical (XML) data model

• Ideal for configuration data, which is tree structured

• No Object-Relational-Mapping (ORM) required

/ dhcp/

aaa/

voip/

defaultLe…

maxLeas…

SubNets/ subNet/

mask

range

lowAddr

highAddr

logFacility

net


Object Relational Mapping (ORM)

Hierarchical Relational

/ dhcp/

aaa/

voip/

defaultLe…

maxLeas…

SubNets/ subNet/

mask

range

lowAddr

highAddr

logFacility

net


ACID

The four properties that define a transaction:

• Atomicity

• Transactions are indivisible, all-or-nothing

• Consistency

• Transactions are all-at-once

• {create A, create B} and {create B, create A} are identical

• Independence

• Transactions do not interfere with each other

• Durability

• Committed data remains in the system even in case of a restart, etc


Database Storage

MO = Managed Object(i.e. configuration consumer)

JOURNAL

START TRANSACTION

WRITE 14 TO

/some/leaf/somewhere

WRITE “hello” TO

/some/other/leaf

COMMIT

START TRANSACTION

WRITE -1 TO /foo/bar

ABORTED

START TR

ON DISK

Values storedbinary

Paths stored assequences of32-bit hashes

ConfD

CDBIN MEMORY

MOMO

MO


Data Model Becomes Database Schema

Network

Element

NETCONF SNMP REST CLI Web

CDB

DatabaseData Provider API

CDB API


OSS/BSS

App AppApp

ConfD Core Engine

App

External

DatabaseOperational

Data

App


Auto-rendered management interfaces and data schema

YANGData Models


JOURNAL

ConfD

CDBIN MEMORY

MOMO

MO

Database Replication

ACTIVE NODE

Journalrecords

JOURNAL

ConfD

CDBIN MEMORY

MOMO

MO

STANDBY NODE


CDB Start

• CDB in-memory contents blank at this point

• Read up schema from disk

• Start transaction

• Read up data from disk

• Data on disk consistent with schema?• If not: Trigger automatic schema upgrade (see next page)

• CDB doesn’t differentiate between up- or downgrade, it just notices that the schema is different

• CDB does not rely on version in the namespace declaration

• Validate

• Commit


CDB Automatic Schema Upgrade

• Elements with default value added to schema• Default values added to new database

• Elements removed from schema• Values removed from new database

• Elements with trivial type changes• Value promoted to new type in new database

• Data is converted to string representation, then to new type

• Elements with complex type changes• No value in new database

• All other elements• Copied as is to new database

Check the devel.log for messages about what conversions were made


CDB Programmatic Schema Upgrade

Then add your own upgrade clients

• Complement to the automatic schema upgrade

• Connect in start phase 0

• Compute values for the new database

• Read any old or new database values

• Compute new values

• Write (overwrite) new values

• If the schema is changed cautiously,CDB automatic schema upgrade might be able to handle everything


CDB Schema Upgrade Examples

• 32-bit flag field becomes 64-bits

• New flags should be initialized to all zeros

• Automatic upgrade sufficient

• New Maximum Transfer Unit (MTU) field added

• Should be 1500 for Eth interfaces, 48 for ATM interfaces

• Upgrade client reads InterfaceType value, classifies it and writes the appropriate MTU value

• InterfaceType changed from string to enumeration

• All strings that match enumeration value are auto upgraded

• Remaining values left unset: set by upgrade client

• Time field changed from seconds to nanoseconds

• Upgrade client reads the old value, multiplies by 109 and overwrites the automatically promoted value


Data Stores

• Each data store is a full copy of the configuration• Each data store can be mapped to CDB or external data base

• Running can be split across CDB and several data bases

• 5 combinations (S+Rro, S+R, R, R+C, Rro+C)

• Operational data store• Store status, performance or application data

CandidateStart-up Running

Operational


Data Stores

• Start-up

• If enabled, start-up configuration is copied to (overwriting) the running configuration at system start

• If not enabled, configuration in running remains unchanged from last time system was running

• The first time the system starts, configuration is read from factory default files ( *_init.xml )

• Running

• Holds the currently running configuration

• Candidate

• Data store for future configuration under construction

• Copied to running to make it take effect


Sessions

• Session Start (login)• Display values

• Update values

• Request Commit• Lock data store (running, candidate, start-up)

• Run validation sequence

• Run Transaction (next slide)

• Wait for acknowledgement from standby node(s)

• Inform subscribers of changes

• Unlock data store

• Session Continues


Transactions


The Life of a Managed Object

• Subscribe to relevant configuration changes

• Read out configuration at startup

• Enter event loop

• If subscription event, react to configuration change

RESTCLINETCONF SNMP


Managed Object API

MO MO

CDB

ConfD Core Engine

CDB API

Data Provider API

Web


Read out Configuration at Startup

• Initialization• cdb_connect()• cdb_start_session()• cdb_set_namespace()

• Read elements• cdb_get_u_int32()• cdb_get_bool()• cdb_get_str()• cdb_get_ipv4()• cdb_get_enum_hash()• … (~30 more)

• Read many• cdb_get_object()• cdb_get_values()

• Count elements• cdb_exists()• cdb_num_instances()

• Move in data tree• cdb_cd()• cdb_pushd()

• Finalization• cdb_end_session()• cdb_close()



Sessions

• CDB protected with Single Writer-Multiple Reader lock

• No configuration changes can occur between cdb_start_session() and cdb_end_session()

• Don’t keep the session open unnecessarily, delays configuration changes

• Timeout after some minutes

Namespaces

• Each data model is defined in an XML Namespace

• ConfD handles multiple data models/namespaces

• Each subsystem should be separate namespace

• Generate header file with namespace hash constant

sock = socket(PF_INET, SOCK_STREAM, 0);

cdb_connect(sock, CDB_READ_SOCKET, &confd_ip_port, size);

cdb_start_session(sock, CDB_RUNNING);

cdb_set_namespace(sock, dhcpd__ns);



Keypaths

• Each element in CDB is addressed by its pathcdb_get_duration(sock, &dur, “/dhcp/defaultLeaseTime”)

• Paths may include keyscdb_get_ipv4(sock,&ip,”/dhcp/SubNets/subNet{10.0.0.0 255.0.0.0}/lowAddr”)

cdb_get_ipv4(sock, &ip, ”/dhcp/SubNets/subNet{%s %s}/lowAddr”, net, mask)

cdb_get_ipv4(sock, &ip, ”/dhcp/SubNets/subNet{%x %x}/lowAddr”, net, mask)

• Index may be used in place of keysn = cdb_num_instances(sock, "/dhcp/SubNets/subNet");

for (i=0; i<n; i++) {

cdb_cd(sock, "/dhcp/SubNets/subNet[%d]", i);

do_subnet(…);

}


Triggers when

anything in

scope changes

Subscribe to Configuration Changes

subsock = socket(PF_INET, SOCK_STREAM, 0);

cdb_connect(subsock, CDB_SUBSCRIPTION_SOCKET, &confd, size);

cdb_subscribe(subsock, 3, dhcpd__ns, &spoint, "/dhcp");

cdb_subscribe_done(subsock);

/ dhcp/

aaa/

voip/

defaultLe…

maxLeas…

SubNets/ subNet/

mask

range

lowAddr

highAddr

logFacility

net

Managed Objects typically have several subscription points


Enter Event Loop

• Event loop needs to monitor subscription socket

• Typically using poll()/select()

while(1) {

set[0].fd = subsock;

set[0].events = POLLIN;

set[0].revents = 0;

poll(set, 1, -1); // Monitor one socket, wait forever

if (set[0].revents & POLLIN) {

cdb_read_subscription_socket(subsock, sub_points, &reslen);

// React on changes here…

// sub_points[] contains triggering subscription points,

// reslen how many

}

cdb_sync_subscription_socket(subsock, CDB_DONE_PRIORITY);

}

• How to handle CDB subscription notifications will be covered in the training module “CDB Subscribers”

Module 9: CDB Technical Intro

Technology

Transcript of Module 9: CDB Technical Intro