Architectural synthesis Flashcards

Question

Which patterns can be used with the component interaction viewpoint?

Answer 1

Client-sever peer to peer publish/subscribe implicit invocation

Answer 2

Problem: two distributed components need to communicate, one needing the service of another --------------------------------------- The CLIENT-SERVER pattern distinguishes two kinds of components: clients and servers. The client requests information or services from a server. To do so it needs to know how to access the server, that is, it requires an ID or an address of the server and of course the server’s interface. The server responds to the requests of the client, and processes each client request on its own. It does not know about the ID or address of the client before the interaction takes place

Answer 3

Problem: how to have a network in which there is no single point of failure? -------------------------------------------- In the PEER-TO-PEER pattern each component has equal responsibilities, in particular it may act both as a client and as a server. Each component offers its own services (or data) and is able to access the services in other components. The PEER-TO-PEER network consists of a dynamic number of components. A PEER-TO-PEER component knows how to access the network. Before a component can join a network, it must get an initial reference to this network ---------------------------------- Advantage: - No single point of failure - Extremely scalable ------------------------------ Disadvantages - Clients contribute a lot of resources (prohibitive on mobile phones) - Can’t bad bad actors

Answer 4

Problem: Event consumers and producers should be decoupled. Many consumers should receive events from one producer --------------------------------------------------- PUBLISH-SUBSCRIBE allows event consumers (subscribers) to register for specific events, and event producers to publish (raise) specific events that reach a specified number of consumers. The PUBLISH-SUBSCRIBE mechanism is triggered by the event producers and automatically executes a callback-operation to the event consumers. The mechanism thus takes care of decoupling producers and consumers by transmitting events between them.

Answer 5

In the Distribution View the system is viewed as a number of components that are distributed among network nodes (or different processes). The components are physically located in different network nodes or processes. They interact with each other through connectors that pass invocations or data from one to another. The details of these interactions can be better explained in the Component Interaction View. ---------------------------------------- * How do the distributed components interact with each other? * How are the distributed components decoupled from each other? * How are the quality attributes of interoperability, location-transparency, performance, and modifiability supported?

Answer 6

Message queue Broker Microservices Monolith?

Answer 7

Problem: Invocations need to be sent over a network and be robust to outages of the receiver; also asynchronous communication is needed. ---------------------------------- Producer puts request into a queue - and can continue to operate Consumer pulls requests from the queue and processes Senders and receivers are decoupled in time and space

Answer 8

Problem: how do we update a consumer about a state change while keeping them decoupled from the producers --------------------------------------- Consumers “subscribe” to events and receive notifications when they occur. ---------------------------------------- Producer is not aware of the consumer who receives it --------------------------------------- The event broker in the middle - allows both parties to scale and evolve in a loosely coupled manner - might stores events or not ---------------------------------------- Challenges: Broker should be - scalable - high performant - fault-tolerant

Answer 9

Problem: You need a highly available and scalable system / you have hundreds of developers and you need to give evolve differently ---------------------------------------------------- Services - run independently - deployed independently - can use different technologies - can be scaled independently ------------------------------------ Challenges - communication complexity (CAP theorem: consistency, availability, and partitioning… => eventual consistency) - performance - return of the monolith

Answer 10

a monolith refers to a software application or system that is built as a single, self-contained unit. It is characterized by having all of its components tightly coupled together and running within a single deployment artifact, such as a single executable or a single web application. ---------------------------------------- Key characteristics: - Single process - Tight coupling - Scalability Challenges - Deployment and versioning

Answer 11

- Proposed architecture defines the framework in which the rest of the development will fit in - Think monolith vs. microservices ---------------------------------- - Forces you to think deep upfront - Even if often it must be iterated (just as in real architecture)

Answer 12

proposing a collection of architecture solutions to address the ASR that are identified during architectural analysis. This activity links the problem to the solution space.

Answer 13

Stakeholders do not necessarily know what they want or are unable to tell all they know.

Answer 14

We can fake it. Fake end result = appears as if a rational process was followed: - Requirements are clear, - design is well-described, - it is argued that design meets requirements

Answer 15

1. Choose architectural style(s)/patterns according to quality requirements --------------------------------------------------- 2. Create overall, tentative structure Q1: What is the context of the system? Describe tentatively the other systems and actors the system interacts with Q2: What functionality is needed? Describe tentatively components (i.e. functionality) & connectors Describe where components are to be deployed Q3: How do you divide the work of implementing functionality? Describe tentative modules (e.g. packages). The result of (2) is the set of initial architectural UML models corresponding to the 3+1 approach ------------------------------------------------- 3. Refine initial structure through quality attribute scenarios: For each quality attribute scenario apply architectural tactics for the main quality attribute. Consider applying tactics also for quality attributes for which you do not have scenarios. (The result of (3) are refined UML models) ----------------------------------------------------- 4. Consider architectural and business qualities. Conceptual integrity – Could you increase integrity by doing similar things in similar ways? Correctness and completeness - Do you cover functional requirements correctly? Feasibility - With the resources available, is it possible to realize the system? ---------------------------------------------------- 5. Maintain an architectural backlog * For each step, note questions and uncertainty in the backlog * Many decisions might need to be taken when more information is available – Detailed design, architectural prototyping, implementation …

Answer 16

Architectural decisions that influence the achievement of quality attribute. They directly affect system’s response to a stimulus. Collection of tactics = strategy E.g., Heartbeat to control availability ----------------------- If no pattern exists for a given goal, tactics can construct a solution from “first principles”

Answer 17

1. Availability 2. Modifiability 3. Performance 4. Security 5. Testability 6. Usability 7. Interoperability

Answer 18

Availability tactics, therefore, are designed to enable a system to endure system faults so that a service being delivered by the system remains compliant with its specification ------------------------- Availability tactics … keep *faults* from becoming *failures*!

Answer 19

when the system no longer delivers a service consistent with its specification – observable by the users

Answer 20

A fault is a malfunction that has the potential to cause a failure.

Answer 21

Detect faults Recover from faults Prevent faults

Answer 22

Monitor Ping/Echo Heartbeat Timestamp Condition Monitoring Sanity checking Voting Exception Detection Self-Test

Answer 23

Preparation and repair --> Redundant spare rollback exception handling software upgrade retry ignore faulty behavior graceful degradation reconfiguration ------------------------------------ reintroduction --> shadow state resynchronization escalating restart nonstop forwarding

Answer 24

Removal from service transaction predictive model exception prevention increase competence set

Answer 25

Ping/echo: request/response message pair exchanged between nodes, used to determine reachability and the round-trip delay through the associated network path. ------------------ Heartbeat: a periodic message exchange between a system monitor and a process being monitored. ---------------- Monitor: a component used to monitor the state of health of other parts of the system. A system monitor can detect failure or congestion in the network or other shared resources, such as from a denial-of-service attack. -------------------- Voting: to check that replicated components are producing the same results. Comes in various flavors: replication, functional redundancy, analytic redundancy. ------------------ Exception Detection: detection of a system condition that alters the normal flow of execution, e.g. system exception, parameter fence, parameter typing, timeout. --------------------- Self-test: procedure for a component to test itself for correct operation. ---------------------- Timestamp: used to detect incorrect sequences of events, primarily in distributed message- passing systems. --------------------------- Sanity Checking: checks the validity or reasonableness of a component’s operations or outputs; typically based on a knowledge of the internal design, the state of the system, or the nature of the information under scrutiny.

Answer 26

Active Redundancy (hot spare): all nodes in a protection group receive and process identical inputs in parallel, allowing redundant spare(s) to maintain synchronous state with the active node(s). ------------------------------ Passive Redundancy (warm spare): only the active members of the protection group process input traffic; one of their duties is to provide the redundant spare(s) with periodic state updates ------------------------------. Spare (cold spare): redundant spares of a protection group remain out of service until a fail-over occurs, at which point a power-on-reset procedure is initiated on the redundant spare prior to its being placed in service ----------------------- Exception Handling: dealing with the exception by reporting it or handling it, potentially masking the fault by correcting the cause of the exception and retrying. -------------------- Rollback: revert to a previous known good state, referred to as the “rollback line”. --------------------- Retry: where a failure is transient retrying the operation may lead to success. ------------------- Ignore Faulty Behavior: ignoring messages sent from a source when it is determined that those messages are spurious. ------------------- Degradation: maintains the most critical system functions in the presence of component failures, dropping less critical functions. ----------------------- Shadow: operating a previously failed or in-service upgraded component in a “shadow mode” for a predefined time prior to reverting the component back to an active role. ------------------ Escalating Restart: recover from faults by varying the granularity of the component(s) restarted and minimizing the level of service affected.

Answer 27

Removal From Service: temporarily placing a system component in an out-of-service state for the purpose of mitigating potential system failures -------------------- Transactions: bundling state updates so that asynchronous messages exchanged between distributed components are atomic, consistent, isolated, and durable. --------------------- Predictive Model: monitor the state of health of a process to ensure that the system is operating within nominal parameters; take corrective action when conditions are detected that are predictive of likely future faults.

Answer 28

Tactics to control modifiability have as their goal controlling the complexity of making changes, as well as the time and cost to make changes.

Answer 29

Increase cohesion Reduce Coupling Defer Binding

Answer 30

Split module Redistribute responsibilities

Answer 31

Encapsulate Use an intermediary Abstract Common services Restrict Dependencies

Answer 32

Component replacement Couple-time parameterization Aspects Configuration-time binding resource files discovery interpret parameters shared repositories polymorphism

Answer 33

Split Module: If the module being modified includes a great deal of capability, the modification costs will likely be high. Refining the module into several smaller modules should reduce the average cost of future changes. ------------------------------------------------- Increase Semantic Coherence: If the responsibilities A and B in a module do not servethe same purpose, they should be placed in different modules. This may involve creating a new module or it may involve moving a responsibility to an existing module.

Answer 34

Encapsulate: Encapsulation introduces an explicit interface to a module. This interface includes an API and its associated responsibilities, such as “perform a syntactic transformation on an input parameter to an internal representation.” ---------------------- Use an Intermediary: Given a dependency between responsibility A and responsibility B (for example, carrying out A first requires carrying out B), the dependency can be broken by using an intermediary. ------------------------- Restrict Dependencies: restricts the modules which a given module interacts with or depends on

Answer 35

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

Answer 36

The goal of performance tactics is to generate a response to an event arriving at the system within some time-based constraint. The event can be single or a stream and is the trigger to perform computation. Performance tactics control the time within which a response is generated

Answer 37

Control Resource Demand Manage Resources

Answer 38

Manage work requests Limit event response Prioritize events Reduce computational overhead Bound execution Times Increase efficiency

Answer 39

Increase resources Introduce concurrency Maintain multiple copies of computations Maintain multiple copies of data Bound queue sizes Schedule resources

Answer 40

Manage Sampling Rate: If it is possible to reduce the sampling frequency at which a stream of data is captured, then demand can be reduced, typically with some loss of fidelity. -------------------- Limit Event Response: process events only up to a set maximum rate, thereby ensuring more predictable processing when the events are actually processed. ------------------- Prioritize Events: If not all events are equally important, you can impose a priority scheme that ranks events according to how important it is to service them. ---------------------- Reduce Overhead: The use of intermediaries (important for modifiability) increases the resources consumed in processing an event stream; removing them improves latency. (e.g. Eclipse) ----------------------- Bound Execution Times: Place a limit on how much execution time is used to respond to an event. (e.g. finding bugs)

Answer 41

Increase Resources: Faster processors, additional processors, additional memory, and faster networks all have the potential for reducing latency. -------------------------- Increase Concurrency: If requests can be processed in parallel, the blocked time can be reduced. Concurrency can be introduced by processing different streams of events on different threads or by creating additional threads to process different sets of activities. ---------------------------- Maintain Multiple Copies of Computations: The purpose of replicas is to reduce the contention that would occur if all computations took place on a single server. -------------------------------- Maintain Multiple Copies of Data: keeping copies of data (possibly one a subset of the other) on storage with different access speeds. (E.g. in-memory caching) ------------------------ Schedule Resources: When there is contention for a resource, the resource must be scheduled. – FIFO – Fixed-priority scheduling – Dynamic priority scheduling – Static scheduling

Answer 42

CIA - Confidentiality is the property that data or services are protected from unauthorized access - Integrity is the property that data or services are not subject to unauthorized manipulation - Availability is the property that the system will be available for legitimate use.

Answer 43

One method for thinking about how to achieve security in a system is to think about physical security. Secure installations have limited access (e.g., by using security checkpoints), have means of detecting intruders (e.g., by requiring legitimate visitors to wear badges), have deterrence mechanisms such as armed guards, have reaction mechanisms such as automatic locking of doors, and have recovery mechanisms such as off-site backup

Answer 44

Detect Attacks Resist Attacks React to Attacks Recover from Attacks

Answer 45

Detect intrusion Detect Service Denial Verify Message Integrity Detect Message Delivery Anomalies

Answer 46

Identify actors Authenticate Actors Authorize Actors Limit access Limit Exposure Encrypt Data Separate entities Validate input Change credential settings

Answer 47

Revoke Access Restrict login Inform actors

Answer 48

Audit Nonrepudiation

Answer 49

Detect Intrusion: compare network traffic or service request patterns within a system to a set of signatures or known patterns of malicious behavior stored in a database. ----------- Detect Service Denial: comparison of the pattern or signature of network traffic coming into a system to historic profiles of known Denial of Service (DoS) attacks. ---------- Verify Message Integrity: use techniques such as checksums or hash values to verify the integrity of messages, resource files, deployment files, and configuration files.

Answer 50

Authenticate Actors: ensure that an actor (user or a remote computer) is actually who or what it purports to be. -------------------- Authorize Actors: ensuring that an authenticated actor has the rights to access and modify either data or services. --------------------- Limit Access: limiting access to resources such as memory, network connections, or access points (e.g. not every user should be able to delete tables from DB) ----------------------- Encrypt Data: apply some form of encryption to data and to communication.

Answer 51

Revoke Access: limit access to sensitive resources, even for normally legitimate users and uses, if an attack is suspected. ------------ Inform Actors: notify operators, other personnel, or cooperating systems when an attack is suspected or detected.

Answer 52

Audit: keep a record of user and system actions and their effects, to help trace the actions of, and to identify, an attacker.

Answer 53

The goal of tactics for testability is to allow for easier testing when an increment of software development is completed

Answer 54

Control and observe system state Limit complexity

Answer 55

Specialized interfaces record/playback localize state storage abstract data sources sandbox executable assertions

Answer 56

Limit structural complexity Limit nondeterminism

Answer 57

usability is concerned with how easy it is for the user to accomplish a desired task, as well as the kind of support the system provides to the user. Researchers in human-computer interaction have used the terms user initiative, system initiative, and mixed initiative to describe which of the human-computer pair takes the initiative in performing certain actions and how the interaction proceeds.

Answer 58

Support user initiative Support system initiative

Answer 59

Cancel Undo Pause/Resume Aggregate

Answer 60

Maintan Task Model Maintain User Model Maintain System Model

Answer 61

Interoperability is the ability of systems or components to exchange and interpret data or services correctly, regardless of their differences in implementation, platforms, or technologies.

Answer 62

Locate Manage interfaces

Answer 63

Discover service

Answer 64

Orchestrate Tailor Interface