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<p>Reactive Systems
Dave Farley
http://www.davefarley.net
@davefarley77
Dave Farley
http://www.davefarley.net
@davefarley77
http://www.continuous-delivery.co.uk
Reactive Systems
21st Century Architecture for 21st Century Problems
Our World Is Changing
Large Applications circa 2005:
• 10’s of Servers
• Seconds of Response Time
• Hours of Offline Maintenance
• Gigabytes of Data

Large Applications Now:
• Handheld Devices to 1000’s of multi-core
processors
• Millisecond Response Time
• 100% Uptime
• Petabytes of Data
Our World Is Changing
The Reactive Manifesto
Responsive
Elastic
Resilient
Message Driven
“21st Century Problems are not best solved with
20th Century Software Architecturesâ€
The Evolution of modern hardware has changed many of
the common assumptions of software development
Source: www.reactivemanifesto.org
Reactive Systems Are:
Responsive:
• Responds in a Timely Manner
• Cornerstone of Usability
• Also Quick to Detect Problems
Reactive Systems Are:
Resilient:
• Remains Responsive in the Face of Failure
• Resilience Depends on - Replication,
Containment, Isolation and Delegation
Reactive Systems Are:
Elastic:
• Remains Responsive Under
Varying Workload
• Responds to Change in the
Input Rate By Increasing or
Decreasing Resources that
Service the Input
• Decentralised Architecture,
No Contention Points, No
Central Bottlenecks
Reactive Systems Are:
Message Driven:
• Asynchronous Message Passing is the foundation
for all of these properties
• Loose-Coupling, Isolation, Location Transparency
• Ability to Delegate Errors
Properties of Reactive Systems
• Flexible
• Loosely-Coupled
• Scalable
• Easier to Develop
• More Tolerant of Failure
• Respond to Failure Gracefully
• Responsive to Users
Fractal Architecture
• Large Systems Are Composed of Smaller Ones
• They Depend on the Reactive Properties of Their
Constituents
• These Benefits Operate At All Scales
• Such Systems are Composable
Failure Modes in Syn