Software Architectural Tactics

Availability Tactics

Fault Detection

• Ping/echo
• Heartbeat (dead man timer_
• Exceptions

Fault Recovery

• Voting
• Active redundancy (hot restart)
• Passive redundancy (warm restart, dual/triple redundancy
• Spare
• Shadow operation
• State resynchronisation
• Checkpoint/rollback

Fault Prevention

• Removal from service
• Transactions
• Process monitor

Modifiability Tactics

Localise Modifications

• Maintain semantic coherence
• Anticipate expected changes
• Generalise the module
• Limit the possible options
• Abstract common services

Prevent Ripple Effects

• Hide information
• Maintain existing interfaces
• Restrict communication paths
• Use an intermediary

Defer Binding Time

• Runtime registration
• Configuration files
• Polymorphism
• Component replacement
• Adherence to defined protocols

Performance Tactics

Resource Demand

• Increase computational efficiency
• Reduce computational overhead
• Manage event rate
• Control frequency of sampling
• Bound execution times
• Bound queue size

Resource Management

• Introduce concurrency
• Maintain multiple copies of either data or computations
• Increase available resources

Resource Arbitration

• First-in/First-out (FIFO)
• Fixed-priority scheduling
• Dynamic priority scheduling
• Static scheduling

Security Tactics

Resisting Attacks

• Authenticate users
• Authorize users (access control, user groups)
• Maintain data confidentiality
• Maintain integrity
• Limit exposure
• Limit access

Detecting Attacks

• Intrusion detection

Recovering from Attacks

• State restoration (see Availability tactics)
• Maintain audit trail (identify attacker)

Testability Tactics

Manage Input/Output

• Record/playback
• Separate interface from implementaiton
• Specialize access routes/interfaces

Internal Monitoring

• Built-in monitors

Usability Tactics

Runtime Tactics

Support user initiative (error correction, e.g. cancel, undo; user efficiency, e.g. aggregate, multiple views)

Support system initiative (maintain user/task/system models)

Design-Time Tactics

• Separate the user interface (e.g. MVC)

Reference

Len Bass, Paul Clements, Rick Kazman, Software Architecture in Practice (2nd ed.). Addison-Wesley, 2003.