5 - Pub Sub Flashcards
Advantages of client server
Easy
Thin clients
Drawbacks of client server
Interaction one to one
Each entitty must know how to address partner
Both must be available
Inherently synchronous
Only pull based
Pub Sub
Distributed Event based systems
Stores subscriptions and correctly delivers event notifs
Publishers (producers)
publish structured events to a service
Subscribers (consumers)
Register interest in particular events through subscriptions
Examples of Pub Sub
Live data broadcasting
Monitoring
Cooperation
Ubiquitous Computing
Characteristics of Pub/Sub system
Heterogeneous (distinct components can be made to work together)
Asynchronous
Space coupled
Comms directed to receiver
Space uncoupled
Sender does not need to know receiver identity
Time coupled
Receiver must exit at that time
Time uncoupled
Sender and receiver can have independent lifetimes
Channel based subscriptions
Subscribe to entire channel
Simple
No interplay between channels
Topic based subscriptions
(think about how the topics are laid out)
Topics organised hierarchically in subtree
Subscribing means receiving all messages to this node and below
Content based subscriptions
Subscribers define predicates (constraints) on attribute values of events
Event Schema
Un-typed set of typed attributes.
<attr-name, attr-type, attr-value>
Subscription Schema
A set of triplets of the form
<attr-name,attr-type,attr-value-predicate>
Specifies values of interest
Centralised model
Central server acts as event broker
Event matching steps
Subscription processing (index and store them)
Event processing (identify matched subscriptions)
Event delivery (to clients)
Distributed Model
Sys of network of brokers.
Each local broker has its own matching engine
Serverless - what is it and when is it used?
cloud native platform
short running, stateless computations
event-driven apps
scale up and down
charged by use
When are cloud functions triggered
By events
Stateful vs Stateless
Apps that track state vs do NOT
Why must states be kept separate to cloud functions?
Function instances are destroyed after use
Advantages of serverless
Cheaper (at low use)
Scalable
More time devoted to user experience
Disadvantages of serverless
Vendor lockin
Staff retraining to rearchitect apps
In large data scenarios, why might system and network delays affect real time alerts?
Lack of bandwitch, large data latency. Cannot reach aggregation point in time.
Lack of scalability for processing large data
