XXX FIXME: confd documentation is outdated.

Configuration service (confd) is designed to work as a part of user-space configuration service, driven by request handler and provides a "FOP-based" interface for accessing Motr configuration information stored in configuration db. Confd is run within the context of a request handler.

Confd pre-loads configuration values fetched from configuration db in memory-based data cache to speed up confc requests.

Data Structures

m0_confd — represents configuration service instance registered in request handler, stores structures to perform caching, accesses to configuration db and handles configuration data requests.
m0_confd_cache – represents an efficient, high concurrency, in-memory cache over the underlying database.

Members:
m0_confd_cache::ca_db is a database environment to access configuration db.
m0_confd_cache::ca_cache is a registry of cached configuration objects.

Confd receives multiple configuration requests from confcs. Each request is a FOP containing a "path" of a requested configuration value to be retrieved from the configuration db. Confcs and confds use RPC layer as a transport to send FOPs.

The following FOPs are defined for confd (see conf/onwire.h):

m0_conf_fetch — configuration request;
m0_conf_fetch_resp — Confd's response to m0_conf_fetch;
m0_conf_update — Update request;
m0_conf_update_resp — Confd's response to m0_conf_update;

Subroutines

m0_confd_register() - registers confd service in the system.
m0_confd_unregister() - unregisters confd service.

Initialization and termination

Confd is initiated and put into operation by request handler logic, after motr is started. Confd service should be registered in request handler with m0_confd_register() call, where it has to initialise own data structures and FOPs used for communication.

Initial configuration database is manually created prior to startup. Confd assumes that:

configuration db is created before confd started;
the schema of configuration database conforms to the expected schema.

The following errors may occur while using the configuration db:

db is empty or is in an unrecognized format;
db schema does not conform to HLD of Motr’s configuration database schema : For documentation links, please refer to this file : doc/motr-design-doc-list.rst

While initialization process, confd has to preload internal cache of configuration objects with their configuration values. It loads entire configuration db into memory-based structures. Pre-loading details can be found in Logical Specification.

Initialised confd may be eventually terminated by m0_confd_unregister() in which confd has to finalise own data structures and FOPs.

After a confd instance is started it manages configuration database, its own internal cache structures and incoming FOP-requests.

Command Usage

To configure confd from console, standard options described in Motr Setup in cs_help() function are used.

Recipes

Typical interaction between confc and confd

Client sends a m0_conf_fetch FOP request to confd;

Configuration service processes confc requests in m0_fom_ops::fo_tick() function of m0_conf_fetch FOP request and sends m0_conf_fetch_resp FOP back.

See also: Configuration Service (confd)