Information Technology Reference
In-Depth Information
Tip 2
: The User Event Bus must deliver messages to listeners in a secure and
reliable way
The User Event Bus has certain required characteristics:
Secure subscription model: A system may register an interest in user
events by subscribing to them. Systems must be validated at the time
they subscribe using an authentication scheme that is supported by the
queue or broker product used. This prevents unauthorised systems and
applications from tapping into the bus to listen on user provisioning
messages. The bus may additionally encrypt messages to prevent
eavesdropping by third parties.
Persistent messages: User provisioning messages are crucial for
downstream systems and cannot afford to be lost, otherwise the loss of
synchronisation will lead to many application errors or even security
breaches. Hence messages must be persisted so that they can be
recovered even if the bus crashes.
Durable subscriptions: Given a large enough ecosystem, some system or
the other is bound to be offline at any given time. User provisioning
messages must eventually be delivered to all of them even if they were
offline at the time the event occurred. The bus must therefore store
messages that should be delivered to a system until it comes back
online.
Guarantee of delivery: When an administrator makes a change to user
data, or when an upstream system makes a REST service call into IAM
making such a change, they need an immediate acknowledgement that
the message will eventually be delivered. It is not feasible to provide a
real-time acknowledgement that the message has been acted upon by
all downstream systems because this is not a synchronous process.
Tip 3
: Manage by exception, and avoid notification of the status of
processing if at all possible
Given the guarantee of eventual delivery, it is sufficient for a downstream
system to quietly process the event. Silence signifies successful processing,
just like in the Unix environment.
Tip 4
: Where notification is unavoidable, use a simple acknowledgement
event on the same bus
