HA CDB synchronization

CDB and CDB API
1

Is there a way to say that CDBs are synchronized between the participating nodes?
Let’s say Node A is the master, B and C are slaves and I’m not going to change the master’s configuration for the moment.

Can I somehow know in node B and C that they are up-to-date?

I tried looking in the notification: CONFD_NOTIF_HA_INFO
Or CONFD_NOTIF_HA_INFO_SYNC – with confd_sync_ha_notification()
But couldn’t understand if it exceeds my expectations.

Thanks

2

When CDB replication is enabled (which it is when high-availability mode is enabled, see /confdConfig/ha in the ConfD config file, default called confd.conf):

For configuration data , replication is done on a per-transaction basis to all the slaves in parallel. When the transaction through for example NETCONF has gone through successfully, all the slaves have been successfully updated too

For operational data (e.g. statistics), replication can be configured to be done asynchronously (best performance) or synchronously in step with the transaction (most secure). With synchronous mode you will know that the participating nodes are in sync for operational data (and always for configuration data).

For more on the ConfD HA functionality see ConfD UG “High Availability” chapter.

You can play with different HA scenarios using the ConfD HA Example, see $CONFD_DIR/examples.confd/ha/dummy/ See README, Makefile, and ctrl.c files.

1 Like
3

So, you mean that if I config /confdConfig/cdb/operational/replicationMode to sync, “confd_ha_beslave()” would block?
(not only operational data?)

Thanks

4

If ‘/confdConfig/cdb/operational/replicationMode’ is set to ‘sync’ the transaction, e.g. over NETCONF, will not go through until all slaves have been updated (in a transaction within that transaction from the master to the slaves).

confd_ha_beslave() behaviour is not affected.

5

Actually, the relevant confd.conf parameter for config/transaction replication is /confdConfig/cdb/replication - /confdConfig/cdb/operational/replication pertains only to operational data in CDB. Please refer to the confd.conf(5) manual page.

6

Sorry, slight typo - while /confdConfig/cdb/operational/replication also pertains only to operational data in CDB, I meant to write /confdConfig/cdb/operational/replicationMode, which was the parameter being discussed. (The naming of the parameters is less than ideal, for “historical reasons”.)

7

Thanks for catching my syntax error Per. Didn’t double check the config parameter. Too quick on the trigger that time. Edited my initial answer for correctness for future reference

8

Is there a way to know in the slave that the transaction is over? Some kind of notification I can look for? for example, can I wait for CONFD_NOTIF_COMMIT_SIMPLE, and when I get it I know the slave is synchronized with the master?

I mean, as another process which is the HAFW, I want to be able to know if a slave is finished synchronizing with the master.

Thanks.

9

Exactly, you can subscribe to CONFD_NOTIF_COMMIT_SIMPLE to be notified of when a transaction has gone through, so for your use-case, when a transaction has gone through at the standby/slave node, the standby node knows that the ConfD CDB database has been updated by the active/master node.

A very good ConfD notifications starting point is the
$CONFD_DIR/examples.confd/misc/notifications
example

Quick demo where I subscribe for CONFD_NOTIF_COMMIT_SIMPLE notifications:

In terminal 1:

$ pwd
/Users/conny/tailf/confd-basic-5.4/examples.confd/misc/notifications
$ make start START_FLAGS=-c
...
/Users/conny/tailf/confd-basic-5.4/bin/confd -c ./confd.conf --addloadpath /Users/conny/tailf/confd-basic-5.4/etc/confd
./confd_notifications -c
Waiting for event notifications...

In terminal 2:

$ netconf-console -i
* Enter a NETCONF operation, end with an empty line
<edit-config>
  <target>
    <running/>
  </target>
  <config xmlns="http://tail-f.com/ns/config/1.0">
    <root xmlns="http://tail-f.com/ns/example/noti">
      <bar>32100</bar>
    </root>
  </config>
</edit-config>

<?xml version="1.0" encoding="UTF-8"?>
<rpc-reply xmlns="urn:ietf:params:xml:ns:netconf:base:1.0" message-id="2">
  <ok/>
</rpc-reply>

In terminal 1 we now see that our application received the CONFD_NOTIF_COMMIT_SIMPLE notification:

Waiting for event notifications...
commit on db 2 from user admin usid 12

See ConfD User Guide called “Notifications” for more info.

Note that if your goal is for the applications in the standby node to be notified of new configuration and react, we recommend that you use the more powerful CDB subscriber interface.

See ConfD Use Guide Chapter called CDB subscriptions and CDB subscription and Intro examples.