Registry database

Starting from the version 3.4, EVA ICS uses structured document database as the primary storage of all configurations. In EVA ICS it is called “document registry system” or just “registry”.


EVA ICS uses YEDB as the structured database. YEDB is fast, easy to repair and crash-free.

Registry server is started with “/opt/eva/sbin/registry-control start” and MUST be always online. When YEDB is upgraded, all EVA ICS components should be stopped (vendor-provided upgrade scripts stop everything automatically).

Registry can be managed with “eva-registry”, “eva registry manage” and “sbin/eva-registry-cli” command-line tools.


Why EVA ICS has been switched to the registry database, instead of using simple “ini” and “json” files:

  • Crash-free storage of configurations, inventory and data objects;
  • easy management with command line tools and API;
  • strict data schemas;
  • unification;
  • easy-to-use SDK.


YEDB configuration is defined in “etc/eva_config”.


It is also possible to use a single registry database for different EVA ICS nodes. if “YEDB_SERVER_ENABLED” is set to “0”, the server is not stared/stopped locally.


It is highly recommended to keep strict data schema (enabled by default).

If configuration file is not created, EVA ICS starts and uses registry server with the default settings.


When deploying / undeploying lots of items, old registry keys are not deleted but moved to the database trash. It is a good idea to clean it from time to time with “eva-registry purge” or “registry_safe_purge” API method.

“.trash” folder can also be used to restore keys deleted by accident.

When key data is changed, the server keeps its 10 backup copies by default, which can be also used to restore data if necessary.

To list deleted and backup copies, use “ls -a” command of “eva-registry” tool.

All data is stored in “runtime/registry” directory, which should not be accessed directly, unless data loss occur.


Each EVA ICS node creates registry key “eva3/<SYSTEM_NAME>”, all data is being stored in its sub-keys.

A strict schema “.schema/eva3/<SYSTEM_NAME>” is created for all data keys, except “userdata” key, which (as well as its subkeys) can contain any fields.

Keys can be edited with “eva-registry” and “eva-registry-cli” CLI tools.

Key user-editable Description
config/common/mailer yes mailer configuration
config/watchdog yes controller watchdog
config/venv yes venv configuration
config/<controller>/main yes primary controller configuration
config/<controller>/apikeys/<key> yes static API keys
config/<controller>/service may startup configuration
config/<controller>/plugins/<plugin> yes plugin configuration
config/uc/datapullers/<datapuller> may datapuller configuration
config/uc/drivers not rec. UC drivers
config/uc/defaults yes item defaults
config/lm/defaults yes item defaults
config/inventory not rec. inventory key (EVA ICS items)
config/data forbidden system objects
config/userdata yes any user-defined data


eva.registry module provides functions for registry management. All functions set key prefix (“eva3/<SYSTEM_NAME>/”) automatically.

The module can be imported and used in plugins, LM PLC macros or anywhere else. When imported by 3rd-party scripts with EVA ICS “lib” directory added to the import path, the module automatically initializes itself with the proper system name and connection settings from “eva_config” file.

eva.registry.config_get(key, **kwargs)

Get key as configuration object


Get keys recursive as a dict

eva.registry.key_as_dict(key, **kwargs)

Work with key as with a dict

with key_as_dict(key): …


Decrement key value


Delete key

eva.registry.key_delete_field(key, field, **kwargs)

Delete key field


Delete keys recursive

eva.registry.key_get(key, default=<class 'KeyError'>)

Get key

eva.registry.key_get_field(key, field, default=<class 'KeyError'>)

Get key field


Get keys recursive as [(key, value)] list

eva.registry.key_import(key, fh)

Import key from stream or file


Increment key value

eva.registry.key_set(key, value, **kwargs)

Set key

eva.registry.key_set_field(key, field, value, **kwargs)

Set key field


Purge database, keep broken keys

Module variables:

  • SYSTEM_NAME name of the current node
  • db YEDB Python object, can be used e.g. to manipulate keys without auto-prefixing.

It is also possible to work with registry server using the official API and clients. See for more details.