.. _configuration: ========================== Configuration and defaults ========================== This document describes the configuration options available for Trigger. If you're using the default loader, you must create or copy the provided :file:`trigger_settings.py` module and make sure it is in ``/etc/trigger/settings.py`` on the local system. .. contents:: :local: :depth: 2 A Word about Defaults ===================== There are two Trigger components that rely on Python modules to be provided on disk in ``/etc/trigger`` and these are: * :mod:`trigger.acl.autoacl` at ``/etc/trigger/autoacl.py`` * :mod:`trigger.conf` at ``/etc/trigger/settings.py`` * :mod:`trigger.changemgmt.bounce` at ``/etc/trigger/bouncy.py`` If your custom configuration either cannot be found or fails to import, Trigger will fallback to the defaults. settings.py ----------- Using a custom settings.py ~~~~~~~~~~~~~~~~~~~~~~~~~~ You may override the default location using the ``TRIGGER_SETTINGS`` environment variable. For example, set this variable and fire up the Python interpreter:: % export TRIGGER_SETTINGS=/home/jathan/sandbox/trigger/conf/trigger_settings.py % python Type "help", "copyright", "credits" or "license" for more information. >>> import os >>> os.environ.get('TRIGGER_SETTINGS') '/home/j/jathan/sandbox/netops/trigger/conf/trigger_settings.py' >>> from trigger.conf import settings Observe that it doesn't complain. You have loaded ``settings.py`` from a custom location! Using global defaults ~~~~~~~~~~~~~~~~~~~~~ If you don't want to specify your own ``settings.py``, it will warn you and fallback to the defaults:: >>> from trigger.conf import settings trigger/conf/__init__.py:114: RuntimeWarning: Module could not be imported from /etc/trigger/settings.py. Using default global settings. warnings.warn(str(err) + ' Using default global settings.', RuntimeWarning) autoacl() --------- The :mod:`trigger.netdevices` and :mod:`trigger.acl` modules require :func:`~trigger.acl.autoacl.autoacl`. Trigger wants to import the :func:`~trigger.acl.autoacl.autoacl` function from either a module you specify or, failing that, the default location. Using a custom autoacl() ~~~~~~~~~~~~~~~~~~~~~~~~ You may override the default location of the module containing the autoacl() function using the ``AUTOACL_FILE`` environment variable just like how you specified a custom location for ``settings.py``. Using default autoacl() ~~~~~~~~~~~~~~~~~~~~~~~ Just as with ``settings.py``, the same goes for :func:`~trigger.acl.autoacl.autoacl`:: >>> from trigger.acl.autoacl import autoacl trigger/acl/autoacl.py:44: RuntimeWarning: Function autoacl() could not be found in /etc/trigger/autoacl.py, using default! warnings.warn(msg, RuntimeWarning) Keep in mind this :func:`~trigger.acl.autoacl.autoacl` has the expected signature but does nothing with the arguments and only returns an empty set:: >>> autoacl('foo') set([]) Configuration Directives ======================== Global settings --------------- .. setting:: PREFIX PREFIX ~~~~~~ This is where Trigger should look for its essential files including :file:`autoacl.py` and :file:`netdevices.xml`. Default:: '/etc/trigger' .. setting:: USE_GPG_AUTH USE_GPG_AUTH ~~~~~~~~~~~~ Toggles whether or not we should use GPG authentication for storing TACACS credentials in the user's ``.tacacsrc`` file. Set to ``False`` to use the old ``.tackf`` encryption method, which sucks but requires almost no overhead. Should be ``False`` unless instructions/integration is ready for GPG. At this time the documentation for the GPG support is incomplete. Default:: False .. setting:: TACACSRC TACACSRC ~~~~~~~~ Sets the location of the ``.tacacsrc`` file. You may override this by setting the ``TACACSRC`` environment variable to the path of the file. Default:: '$HOME/.tacacsrc' .. setting:: TACACSRC_KEYFILE TACACSRC_KEYFILE ~~~~~~~~~~~~~~~~ Only used if GPG auth is disabled. This is the location of the file that contains the passphrase used for the two-way hashing of the user credentials within the ``.tacacsrc`` file. You may override this by setting the ``TACACSRC_KEYFILE`` environment variable to path of the file. Default:: '/etc/trigger/.tackf' .. setting:: DEFAULT_REALM DEFAULT_REALM ~~~~~~~~~~~~~ Default login realm to store user credentials (username, password) for general use within the ``.tacacsrc`` file. Default:: 'aol' .. setting:: FIREWALL_DIR FIREWALL_DIR ~~~~~~~~~~~~ Location of firewall policy files. Default:: '/data/firewalls' .. setting:: TFTPROOT_DIR TFTPROOT_DIR ~~~~~~~~~~~~ Location of the tftproot directory. Default:: '/data/tftproot' .. setting:: INTERNAL_NETWORKS INTERNAL_NETWORKS ~~~~~~~~~~~~~~~~~ A list of ``IPy.IP`` objects describing your internally owned networks. All network blocsk owned/operated and considered a part of your network should be included. The defaults are private IPv4 networks defined by RFC 1918. Default:: [IPy.IP("10.0.0.0/8"), IPy.IP("172.16.0.0/12"), IPy.IP("192.168.0.0/16")] .. setting:: VENDOR_MAP VENDOR_MAP ~~~~~~~~~~ .. versionadded:: 1.2 A mapping of manufacturer attribute values to canonical vendor name used by Trigger. These single-word, lowercased canonical names are used throughout Trigger. If your internal definition differs from the UPPERCASED ones specified below (which they probably do, customize them here. Default:: { 'A10 NETWORKS': 'a10', 'ARISTA NETWORKS': 'arista', 'BROCADE': 'brocade', 'CISCO SYSTEMS': 'cisco', 'CITRIX': 'citrix', 'DELL': 'dell', 'FOUNDRY': 'foundry', 'JUNIPER': 'juniper', 'NETSCREEN TECHNOLOGIES': 'netscreen', } .. setting:: SUPPORTED_PLATFORMS SUPPORTED_PLATFORMS ~~~~~~~~~~~~~~~~~~~ .. versionadded:: 1.2 A dictionary keyed by manufacturer name containing a list of the device types for each that is officially supported by Trigger. Do not modify this unless you know what you’re doing! Default:: { 'a10': ['SWITCH'], 'arista': ['SWITCH'], 'brocade': ['ROUTER', 'SWITCH'], 'cisco': ['ROUTER', 'SWITCH'], 'citrix': ['SWITCH'], 'dell': ['SWITCH'], 'foundry': ['ROUTER', 'SWITCH'], 'juniper': ['FIREWALL', 'ROUTER', 'SWITCH'], 'netscreen': ['FIREWALL'] } .. setting:: SUPPORTED_VENDORS SUPPORTED_VENDORS ~~~~~~~~~~~~~~~~~ A tuple of strings containing the names of valid manufacturer names. These are currently defaulted to what Trigger supports internally. Do not modify this unless you know what you're doing! Default:: ('a10', 'arista', 'brocade', 'cisco', 'citrix', 'dell', 'foundry', 'juniper', 'netscreen') .. setting:: SUPPORTED_TYPES SUPPORTED_TYPES ~~~~~~~~~~~~~~~ A tuple of device types officially supported by Trigger. Do not modify this unless you know what you’re doing! Default:: ('FIREWALL', 'ROUTER', 'SWITCH') .. setting:: DEFAULT_TYPES DEFAULT_TYPES ~~~~~~~~~~~~~ .. versionadded:: 1.2 A mapping of of vendor names to the default device type for each in the event that a device object is created and the ``deviceType`` attribute isn't set for some reason. Default:: { 'a10': 'SWITCH', 'arista': 'SWITCH', 'brocade': 'SWITCH', 'citrix': 'SWITCH', 'cisco': 'ROUTER', 'dell': 'SWITCH', 'foundry': 'SWITCH', 'juniper': 'ROUTER', 'netscreen': 'FIREWALL', } .. setting:: FALLBACK_TYPE FALLBACK_TYPE ~~~~~~~~~~~~~ .. versionadded:: 1.2 When a vendor is not explicitly defined within :setting:`DEFAULT_TYPES`, fallback to this type. Default:: 'ROUTER' Twister settings ---------------- These settings are used to customize the timeouts and methods used by Trigger to connect to network devices. .. setting:: DEFAULT_TIMEOUT DEFAULT_TIMEOUT ~~~~~~~~~~~~~~~ Default timeout in seconds for commands executed during a session. If a response is not received within this window, the connection is terminated. Default:: 300 .. setting:: TELNET_TIMEOUT TELNET_TIMEOUT ~~~~~~~~~~~~~~ Default timeout in seconds for initial telnet connections. Default:: 60 .. setting:: TELNET_ENABLED TELNET_ENABLED ~~~~~~~~~~~~~~ .. versionadded:: 1.2 Whether or not to allow telnet fallback. Set to ``False`` to disable support for telnet. Default:: True .. setting:: SSH_PTY_DISABLED SSH_PTY_DISABLED ~~~~~~~~~~~~~~~~ .. versionadded:: 1.2 A mapping of vendors to the types of devices for that vendor for which you would like to disable interactive (pty) SSH sessions, such as when using ``bin/gong``. Default:: { 'dell': ['SWITCH'], } .. setting:: SSH_ASYNC_DISABLED SSH_ASYNC_DISABLED ~~~~~~~~~~~~~~~~~~ .. versionadded:: 1.2 A mapping of vendors to the types of devices for that vendor for which you would like to disable asynchronous (NON-interactive) SSH sessions, such as when using `~trigger.twister.execute` or `~trigger.cmds.Commando` to remotely control a device. Default:: { 'arista': ['SWITCH'], 'brocade': ['SWITCH'], 'dell': ['SWITCH'], } .. setting:: IOSLIKE_VENDORS IOSLIKE_VENDORS ~~~~~~~~~~~~~~~ A tuple of strings containing the names of vendors that basically just emulate Cisco's IOS and can be treated accordingly for the sake of interaction. Default:: ('a10', 'arista', 'brocade', 'cisco', 'dell', 'foundry') .. setting:: GORC_FILE GORC_FILE ~~~~~~~~~ The file path where a user's ``.gorc`` is expected to be found. Default:: '~/.gorc' .. setting:: GORC_ALLOWED_COMMANDS GORC_ALLOWED_COMMANDS ~~~~~~~~~~~~~~~~~~~~~ The only root commands that are allowed to be executed when defined within a users's ``~/.gorc`` file. Any root commands not specified here will be filtered out by `~trigger.gorc.filter_commands()`. Default:: '~/.gorc' NetDevices settings ------------------- .. setting:: WITH_ACLS WITH_ACLS ~~~~~~~~~ Globally toggle whether to load ACL associations from the Redis database. If you don't have Redis or aren't using Trigger to manage ACLs set this to ``False``. .. note:: If you are doing work that does not require ACL information setting this to ``False`` can speed things up. Several libraries that interact with devices also have a ``with_acls`` argument to toggle this at runtime. Default:: True .. setting:: AUTOACL_FILE AUTOACL_FILE ~~~~~~~~~~~~ Path to the explicit module file for autoacl.py so that we can still perform ``from trigger.acl.autoacl import autoacl`` without modifying ``sys.path``. Default:: '/etc/trigger/autoacl.py' .. setting:: NETDEVICES_FORMAT NETDEVICES_FORMAT ~~~~~~~~~~~~~~~~~ .. deprecated:: 1.3 Replaced by the :setting:`NETDEVICES_LOADERS` plugin system. This variable is no longer used in Trigger 1.3 and will be ignored. One of ``json``, ``rancid``, ``sqlite``, ``xml``. This MUST match the actual format of :setting:`NETDEVICES_FILE` or it won't work for obvious reasons. Please note that RANCID support is experimental. If you use it you must specify the path to the RANCID directory. You may override this location by setting the ``NETDEVICES_FORMAT`` environment variable to the format of the file. Default:: 'xml' .. setting:: NETDEVICES_FILE NETDEVICES_FILE ~~~~~~~~~~~~~~~ .. deprecated:: 1.3 Replaced by :setting:`NETDEVICES_SOURCE`. If you are using Trigger 1.3 or later, please do not define this variable. Path to netdevices device metadata source file, which is used to populate `~trigger.netdevices.NetDevices`. This may be JSON, RANCID, a SQLite3 database, or XML. You must set :setting:`NETDEVICES_FORMAT` to match the type of data. Please note that RANCID support is experimental. If you use it you must specify the path to the RANCID directory. You may override this location by setting the ``NETDEVICES_FILE`` environment variable to the path of the file. Default:: '/etc/trigger/netdevices.xml' .. setting:: NETDEVICES_LOADERS NETDEVICES_LOADERS ~~~~~~~~~~~~~~~~~~ .. versionadded:: 1.3 A tuple of data loader classes, specified as strings. Optionally, a tuple can be used instead of a string. The first item in the tuple should be the Loader's module, subsequent items are passed to the Loader during initialization. Loaders should inherit from `~trigger.netdevices.loader.BaseLoader`. For now, please see the source code for the pre-defined loader objects at ``trigger/netdevices/loaders/filesystem.py`` for examples. Default:: ( 'trigger.netdevices.loaders.filesystem.XMLLoader', 'trigger.netdevices.loaders.filesystem.JSONLoader', 'trigger.netdevices.loaders.filesystem.SQLiteLoader', 'trigger.netdevices.loaders.filesystem.CSVLoader', 'trigger.netdevices.loaders.filesystem.RancidLoader', ) .. setting:: NETDEVICES_SOURCE NETDEVICES_SOURCE ~~~~~~~~~~~~~~~~~ .. versionadded:: 1.3 A path or URL to netdevices device metadata source data, which is used to populate `~trigger.netdevices.NetDevices` with `~trigger.netdevices.NetDevice` objects. For more information on this, see :setting:`NETDEVICES_LOADERS`. This value may be as simple as an absolute path to a file on your local system, or it may be a fully-fledge URL such as ``http://user:pass@myhost.com:8080/stuff?foo=bar#fragment-data``. This URL data is parsed and passed onto a `~trigger.netdevices.loader.BaseLoader` subclass for retrieving device metadata. You may override this location by setting the ``NETDEVICES_SOURCE`` environment variable to the path of the file. Default:: '/etc/trigger/netdevices.xml' .. setting:: RANCID_RECURSE_SUBDIRS RANCID_RECURSE_SUBDIRS ~~~~~~~~~~~~~~~~~~~~~~ .. versionadded:: 1.2 When using `RANCID `_ as a data source, toggle whether to treat the RANCID root as a normal instance, or as the root to multiple instances. You may override this location by setting the ``RANCID_RECURSE_SUBDIRS`` environment variable to any ``True`` value. Default:: False .. setting:: VALID_OWNERS VALID_OWNERS ~~~~~~~~~~~~ A tuple of strings containing the names of valid owning teams for :class:`~trigger.netdevices.NetDevice` objects. This is intended to be a master list of the valid owners to have a central configuration entry to easily reference. Please see the sample settings file for an example to use in your environment. Default:: () .. setting:: JUNIPER_FULL_COMMIT_FIELDS JUNIPER_FULL_COMMIT_FIELDS ~~~~~~~~~~~~~~~~~~~~~~~~~~ Fields and values defined here will dictate which Juniper devices receive a ``commit-configuration full`` when populating `~trigger.netdevices.NetDevice.commit_commands`. The fields and values must match the objects exactly or it will fallback to ``commit-configuration``. Example:: # Perform "commit full" on all Juniper EX4200 switches. JUNIPER_FULL_COMMIT_FIELDS = { 'deviceType': 'SWITCH', 'make': 'EX4200', } Default :: {} Bounce Window settings ---------------------- .. setting:: BOUNCE_FILE BOUNCE_FILE ~~~~~~~~~~~ .. versionadded:: 1.3 The path of the explicit module file containing custom bounce window mappings. This file is expected to define a ``bounce()`` function that takes a `~trigger.netdevices.NetDevice` object as an argument and returns a `~trigger.changemgmt.BounceWindow` object. You may override the default location of the module containing the ``bounce()`` function by setting the ``BOUNCE_FILE`` environment variable to the path of the file. Default:: '/etc/trigger/bounce.py' .. setting:: BOUNCE_DEFAULT_TZ BOUNCE_DEFAULT_TZ ~~~~~~~~~~~~~~~~~ .. versionadded:: 1.3 The name of the default timezone for bounce windows. `Olson zoneinfo names `_ are used for this in the format of *Area/Location*. All `~trigger.changemgmt.BounceWindow` objects are configured using "US/Eastern". Default:: 'US/Eastern' .. setting:: BOUNCE_DEFAULT_COLOR BOUNCE_DEFAULT_COLOR ~~~~~~~~~~~~~~~~~~~~ .. versionadded:: 1.3 The default fallback window color for bounce windows. Must be one of 'green', 'yellow', or 'red'. :green: **Low Risk**. Minor impact on user or customer environments. Backing-out the change, if required, is easily accomplished. User notification is often unnecessary. :yellow: **Medium Risk**. Potential exists for substantially impacting user or customer environments. Backing-out the change, if required, can be accomplished in a reasonable timeframe. :red: **High Risk**. The highest potential impact on users or cutomers. Any non-standard add, move or change falls into this category. Backing-out of a high-risk change may be time-consuming or difficult. Default:: 'red' Redis settings -------------- .. setting:: REDIS_HOST REDIS_HOST ~~~~~~~~~~ Redis master server. This will be used unless it is unreachable. Default:: '127.0.0.1' .. setting:: REDIS_PORT REDIS_PORT ~~~~~~~~~~ The Redis port. Default:: 6379 .. setting:: REDIS_DB REDIS_DB ~~~~~~~~ The Redis DB to use. Default:: 0 .. _db-settings: Database settings ----------------- These will eventually be replaced with another task queue solution (such as Celery). For now, you'll need to populate this with information for your database. These are all self-explanatory, I hope. For more information on database drivers that you may need, please see :ref:`db-drivers`. .. setting:: DATABASE_ENGINE DATABASE_ENGINE ~~~~~~~~~~~~~~~ The database driver you intend to use for the task queue. This can be one of ``postgresql``, ``mysql``, ``sqlite3``. For the purpose of backwards compatibility this defaults to ``mysql``. Default:: 'mysql' .. setting:: DATABASE_NAME DATABASE_NAME ~~~~~~~~~~~~~ The name of the database. If using ``sqlite3``, this is the path to the database file. Default:: '' .. setting:: DATABASE_USER DATABASE_USER ~~~~~~~~~~~~~ The username to use to connect to the database. (Not used with ``sqlite3``) Default:: '' .. setting:: DATABASE_PASSWORD DATABASE_PASSWORD ~~~~~~~~~~~~~~~~~ The password for the user account used to connect to the database. (Not used with ``sqlite``) Default:: '' .. setting:: DATABASE_HOST DATABASE_HOST ~~~~~~~~~~~~~ The host on which your database resides. Set to empty string for localhost. (Not used with ``sqlite3``) Default:: '' .. setting:: DATABASE_PORT DATABASE_PORT ~~~~~~~~~~~~~ The destination port used by the task queue. Set to empty string for default. (Not used with ``sqlite3``) Default:: '' Access-list Management settings ------------------------------- These are various settings that control what files may be modified, by various tools and libraries within the Trigger suite. These settings are specific to the functionality found within the :mod:`trigger.acl` module. .. setting:: IGNORED_ACLS IGNORED_ACLS ~~~~~~~~~~~~ This is a list of FILTER names of ACLs that should be skipped or ignored by tools. These should be the names of the filters as they appear on devices. We want this to be mutable so it can be modified at runtime. Default:: [] .. setting:: NONMOD_ACLS NONMOD_ACLS ~~~~~~~~~~~ This is a list of FILE names of ACLs that shall not be modified by tools. These should be the names of the files as they exist in ``FIREWALL_DIR``. Trigger expects ACLs to be prefixed with ``'acl.'``. Default:: [] .. setting:: VIPS VIPS ~~~~ This is a dictionary mapping of real IP to external NAT IP address for used by your connecting host(s) (aka jump host). This is used primarily by ``load_acl`` in the event that a connection from a real IP fails (such as via tftp) or when explicitly passing the ``--no-vip`` flag. Format: ``{local_ip: external_ip}`` Default:: {} Access-list loading & rate-limiting settings -------------------------------------------- All of the following esttings are currently only used by ``load_acl``. If and when the ``load_acl`` functionality gets moved into the library API, this may change. .. setting:: AUTOLOAD_FILTER AUTOLOAD_FILTER ~~~~~~~~~~~~~~~ A list of FILTER names (not filenames) that will be skipped during automated loads (``load_acl --auto``). This setting was renamed from ``AUTOLOAD_BLACKLIST``; usage of that name is being phased out. Default:: [] .. setting:: AUTOLOAD_FILTER_THRESH AUTOLOAD_FILTER_THRESH ~~~~~~~~~~~~~~~~~~~~~~ A dictionary mapping for FILTER names (not filenames) and a numeric threshold. Modify this if you want to create a list that if over the specified number of devices will be treated as bulk loads. For now, we provided examples so that this has more context/meaning. The current implementation is kind of broken and doesn't scale for data centers with a large of number of devices. Default:: {} .. setting:: AUTOLOAD_BULK_THRESH AUTOLOAD_BULK_THRESH ~~~~~~~~~~~~~~~~~~~~ Any ACL applied on a number of devices >= this number will be treated as bulk loads. For example, if this is set to 5, any ACL applied to 5 or more devices will be considered a bulk ACL load. Default:: 10 .. setting:: BULK_MAX_HITS BULK_MAX_HITS ~~~~~~~~~~~~~ This is a dictionary mapping of filter names to the number of bulk hits. Use this to override :setting:`BULK_MAX_HITS_DEFAULT`. Please note that this number is used PER EXECUTION of ``load_acl --auto``. For example if you ran it once per hour, and your bounce window were 3 hours, this number should be the total number of expected devices per ACL within that allotted bounce window. Yes this is confusing and needs to be redesigned.) Examples: + 1 per load_acl execution; ~3 per day, per 3-hour bounce window + 2 per load_acl execution; ~6 per day, per 3-hour bounce window Format: ``{'filter_name': max_hits}`` Default:: {} .. setting:: BULK_MAX_HITS_DEFAULT BULK_MAX_HITS_DEFAULT ~~~~~~~~~~~~~~~~~~~~~ If an ACL is bulk but not defined in :setting:`BULK_MAX_HITS`, use this number as max_hits. For example using the default value of 1, that means load on one device per ACL, per data center or site location, per ``load_acl --auto`` execution. Default:: 1 On-Call Engineer Display settings --------------------------------- .. setting:: GET_CURRENT_ONCALL GET_CURRENT_ONCALL ~~~~~~~~~~~~~~~~~~ This variable should reference a function that returns data for your on-call engineer, or failing that ``None``. The function should return a dictionary that looks like this:: { 'username': 'mrengineer', 'name': 'Joe Engineer', 'email': 'joe.engineer@example.notreal' } Default:: lambda x=None: x CM Ticket Creation settings --------------------------- .. setting:: CREATE_CM_TICKET CREATE_CM_TICKET ~~~~~~~~~~~~~~~~ This variable should reference a function that creates a CM ticket and returns the ticket number, or ``None``. It defaults to ``_create_cm_ticket_stub``, which can be found within the ``settings.py`` source code and is a simple function that takes any arguments and returns ``None``. Default:: _create_cm_ticket_stub Notification settings --------------------- .. setting:: EMAIL_SENDER EMAIL_SENDER ~~~~~~~~~~~~ .. versionadded:: 1.2.2 The default email sender for email notifications. It's probably a good idea to make this a no-reply address. Default:: 'nobody@not.real' .. setting:: SUCCESS_EMAILS SUCCESS_EMAILS ~~~~~~~~~~~~~~ A list of email addresses to email when things go well (such as from ``load_acl --auto``). Default:: [] .. setting:: FAILURE_EMAILS FAILURE_EMAILS ~~~~~~~~~~~~~~ A list of email addresses to email when things go not well. Default:: [] .. setting:: NOTIFICATION_SENDER NOTIFICATION_SENDER ~~~~~~~~~~~~~~~~~~~ .. versionadded:: 1.2.2 The default sender for integrated notifications. This defaults to the fully-qualified domain name (FQDN) for the local host. Default:: socket.gethostname() .. setting:: SUCCESS_RECIPIENTS SUCCESS_RECIPIENTS ~~~~~~~~~~~~~~~~~~ .. versionadded:: 1.2.2 Destinations (hostnames, addresses) to notify when things go well. Default:: [] .. setting:: FAILURE_RECIPIENTS FAILURE_RECIPIENTS ~~~~~~~~~~~~~~~~~~ .. versionadded:: 1.2.2 Destinations (hostnames, addresses) to notify when things go not well. Default:: [] .. setting:: NOTIFICATION_HANDLERS NOTIFICATION_HANDLERS ~~~~~~~~~~~~~~~~~~~~~ .. versionadded:: 1.2.2 This is a list of fully-qualified import paths for event handler functions. Each path should end with a callable that handles a notification event and returns ``True`` in the event of a successful notification, or ``None``. To activate a handler, add it to this list. Each handler is represented by a string: the full Python path to the handler's function name. Handlers are processed in order. Once an event is succesfully handled, all processing stops so that each event is only handled once. Until this documentation improves, for a good example of how to create a custom handler, review the source code for `~trigger.utils.notifications.handlers.email_handler()`. Default:: [ 'trigger.utils.notifications.handlers.email_handler', ]