Difference between revisions of "Projects/Hierarchical iprop"
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Revision as of 12:20, 6 January 2014
Contents
Description
This project adds the ability for incremental propagation slaves to act as masters for other slaves, forming a hierarchy of masters and slaves. This feature can be useful for controlling propagation load in environments with many slaves, or to address incomplete network connectivity between masters and slaves. The project is based on an existing implementation by Richard Basch.
Background
Since release 1.7, we have had support for incremental propagation for changes to principal information. The slave runs a kpropd daemon in standalone mode, which periodically polls for updates from kadmind on the master, using a GSSRPC-based protocol. Updates are normally transmitted to the slave as marshalled operations in the response to the polling RPC. If the slave drifts too far out of date or if there have been changes to policies on the master, then a full dump is performed from the master to the slave using kprop.
The master and slave store the state needed for incremental propagation in a memory-mapped file called the ulog, which contains a header and a circular array of fixed-size update entries. Each update entry has a timestamp and a serial number; serial numbers begin at 1 and increment for each update. The ulog header contains:
- kdb_hmagic: A magic number (to detect corruption)
- db_version_num: A version number (currently set to 1 and unused by readers)
- kdb_num: The number of updates in the ulog
- kdb_first_time: The timestamp of the ulog's first entry
- kdb_last_time: The timestamp of the ulog's last entry
- kdb_first_sno: The timestamp of the ulog's first entry
- kdb_last_sno: The timestamp of the ulog's last entry
- kdb_state: The stability state of the ulog
- kdb_block: The entry size (normally 2048)
The size of the circular entry array is determined by the iprop_master_ulogsize krb5.conf variable, which is not recorded in the header. There is some redundancy in the header fields; given the array size, any two of kdb_num, kdb_first_sno, and kdb_last_sno, the other value can be computed.
Slaves currently do not use the update entry array and only make use of the kdb_last_sno and kdb_last_time header fields, to track the most recently received update from the master.
