Configuring EFM
===============

TPA will install and configure EFM when ``failover_manager`` is set to
``efm`` .

Note that EFM is only available via EDB’s package repositories and
requires a valid subscription.

EFM configuration
-----------------

TPA will generate ``efm.nodes`` and ``efm.properties`` with the
appropriate instance-specific settings, with remaining settings set to
the respective default values. TPA will also place an
``efm.notification.sh`` script which basically contains nothing by
default and leaves it up to the user to fill it in however they want.
TPA will override the default settings for ``auto.allow.hosts`` and
``stable.nodes.file`` to simplify adding agents to the cluster.

See the :ref:`EFM documentation <Configuring EFM>` 

for more details on EFM configuration.

efm_user_password_encryption
----------------------------

Must be either ``scram-sha-256`` or ``md5``

Set ``efm_user_password_encryption`` to control the ``auth-method`` for
the ``efm`` Postgres user’s ``auth-method`` in ``pg_hba.conf`` as well
as the algorithm used when generating it’s encrypted password.

.. code:: yaml

   efm_user_password_encryption: scram-sha-256 # or can be set to `md5`

efm_conf_settings
-----------------

You can use ``efm_conf_settings`` to set specific parameters. These must
be written as entries in an Ansible dictionary, in ``key: value`` form

See the :ref:`documentation on the `efm.properties` file <Configuring EFM>` 

for details on which settings can be configured.

.. code:: yaml

   cluster_vars:
     efm_conf_settings:
        notification.level: WARNING
        ping.server.ip: <well known address in network>

If you make changes to values under ``efm_conf_settings`` , TPA will
always restart EFM to activate the changes.

EFM witness
^^^^^^^^^^^

TPA will install and configure EFM as witness on instances whose
``role`` contains ``efm-witness`` .

Repmgr
^^^^^^

EFM works as a failover manager and therefore TPA will still install
repmgr for setting up postgresql replicas on postgres versions 11 and
below. ``repmgrd`` i.e. repmgr’s daemon remains disabled in this case
and repmgr’s only job is to provided replication setup functionality.

For postgres versions 12 and above, any cluster that uses EFM will use
``pg_basebackup`` to create standby nodes and not use repmgr in any
form.

Node Promotability
^^^^^^^^^^^^^^^^^^

TPA determines whether a node is eligible for promotion by EFM during
failover based on the node’s role and replication topology. The
following rules are applied when generating the EFM configuration:

- **Witness nodes** (``witness`` role) are never promotable.

- **Nodes with the ``efm-not-promotable`` role** are not eligible for
  promotion. This can be used to prevent specific standbys, such as DR
  or reporting nodes, from being promoted to primary.

- **Cascading standbys** (nodes that are not directly replicating from
  the primary) are also not promotable.

- All other nodes are considered promotable by default.

To explicitly prevent a standby from being promoted, add
``efm-not-promotable`` to the node’s ``roles`` list in your cluster
configuration. This ensures that EFM will not attempt to promote this
node during failover events.