availability_group.api.subscribe(event_id, callback)
Register a function (or a callable object) to be invoked when a specified event occurs.
This can be useful to workflows that need to be aware of changes to an Availability group as
they happen. A workflow should register an event handler using this subscribe function.
For example, a workflow should not perform tasks when the node that they are on is Secondary in the group.
| Parameters | Description |
|---|---|
| event_id (str) |
The ID of the Availability group-related event for which you want to register a callback function. |
| callback (Callable) |
The function to be called when the event happens. |
| EventID | Callback parameter | Type of parameter |
|---|---|---|
| EventId.NODE_ROLE_CHANGED | event_data | NodeRoleChanged |
Example of responding to a request only on Primary node:
from availability_group.api import EventId, NodeRole, NodeRoleChanged, subscribe
role_cached_in_my_workflow: str = None
# Define a custom handler for when the node role has changed.
def ag_hook(event: NodeRoleChanged, **kwargs):
"""Custom handling of the change of the node's role."""
if event.previous:
logger.debug(f"The node started with role '{event.new}'.")
else:
logger.debug(f"The role changed from '{event.previous}' to '{event.new}'.")
global role_cached_in_my_workflow
# Store the new role in a global variable for later use.
role_cached_in_my_workflow = event.new
if event.new == Role.NOT_IN_GROUP:
# Perform the actions specific to when the node is not in a group.
if event.new == Role.PRIMARY:
# Perform the actions specific to when the node becomes the Primary one in a group.
if event.new == Role.SECONDARY:
# Perform the actions specific to when the node becomes the Secondary one in a group.
# Register the custom handler for the event of a change of the node's role.
subscribe(EventId.NODE_ROLE_CHANGED, ag_hook)
@route(app, "/workflow_name/path2")
def get_path2():
global role_cached_in_my_workflow
if role_cached_in_my_workflow == Role.SECONDARY:
return jsonify({
"result": "error",
"message": "Secondary node should not perform the action."
})
# This is reached on a Primary node or an instance that's not in a group.
# Perform the action.
return jsonify({"result": "success"})New in version 22.11.1.