EC

Question 1

What does the characteristic: ‘small in size’ mean for a microservice?

Answer 1

Very compact pieces of software

Measured in lines of code or number of features

Question 2

What does the characteristic: ‘messaging enabled’ mean for a microservice?

Answer 2

Microservices can communicate with each other and between different machines

Question 3

What does the characteristic: ‘bounded by contexts’ mean for a microservice?

Answer 3

Business domain model may be broken down into smaller pieces which bound the boundaries of microservices

Question 4

What does the characteristic: ‘independently deployable’ mean for a microservice?

Answer 4

No microservice depends on another microservice, therefore deployment carries less risk, therefore less testing is required

Question 5

What does the characteristic: ‘built and released with automated processes’ mean for a microservice?

Answer 5

Build tools make the process repeatable and reliable, while version control allows for reversability

Question 6

What does the characteristic: ‘built and released with automated processes’ mean for a microservice?

Answer 6

Build tools make the process repeatable and reliable, while version control allows for reversibility

Question 7

What does the property: ‘technological heterogeneity’ mean for a microservice?

Answer 7

Microservices can be created in any technology in any language, a suite of MS can be written in a variety of langs

Question 8

What does the property: ‘resilience’ mean for a microservice?

Answer 8

MS can mask failures by using timeouts, circuit breakers or bulkheads

Question 9

What does the property: ‘ease of development’ mean for a microservice?

Answer 9

MS can be deployed incrementally and at different speeds making it easier to exploit new business opportunities

Question 10

What does the property: ‘scaling’ mean for a microservice?

Answer 10

MS can be allocated different amounts of computing capacity

Question 11

What does the property: ‘organizational alignment’ mean for a microservice?

Answer 11

Companies can change their organisational structure to correspond with their system structure

Question 12

What does the property: ‘composability’ mean for a microservice?

Answer 12

Microservices can be combined in multiple different ways to meet new business requirements

Question 13

What does the property: ‘replacability’ mean for a microservice?

Answer 13

Replacing portions of an application is easy as applications are small

Question 14

What is the Single Responsibility Principle?

Answer 14

One should gather together those things that change for the same reason, and separate things that change for different reasons

Question 15

What is the Law of Demeter?

Answer 15

The LoD states that one should make components which only know about the structure and properties of components they deal with directly

Question 16

What is the rule of ‘Dont Repeat Yourself’?

Answer 16

One should only merge things that are duplicated to avoid wasting effort making something that is needlessly complicated and hard to maintain

Question 17

What is high-cohesion?

Answer 17

Behaviour related to a microservice is found within that microservice - nowhere else

Question 18

What is loose coupling?

Answer 18

A change to one microservice does not require a change to another - high levels of encapsulation

Question 19

What is the ‘client-server’ property of a system of microservices?

Answer 19

Client deals with UI, server deals with processing and storage

Question 20

What is the ‘stateless’ property of a system of microservices?

Answer 20

The stateless principle means that the session state is kept entirely on the client - none on server

Question 21

What is the ‘cache’ property of a system of microservices?

Answer 21

The client may reuse cached response data for later requests

Question 22

What is the ‘uniform interface’ property of a system of microservices?

Answer 22

Utilize the CRUD operations to manipulate resources

Question 23

What is the ‘layered system’ property of a system of microservices?

Answer 23

The client cannot ‘see’ beyond the immediate layer it is interacting with

Question 24

What is the ‘code-on-demand’ property of a system of microservices?

Answer 24

Client functionality may be extended by downloading applets or scripts

Question 25

What is the 'REST' property of a system of microservices?

Answer 25

Highly cohesive, loosely coupled microsystem designs mean resources will be exchanged using representations of them

Question 26

What are 'documents' in the context of microservices?

Answer 26

Akin to a file - can contain data or links to other resources - CRUD available

Question 27

What are 'collections' in the context of microservices?

Answer 27

Akin to a directory of resources - can only CREATE or READ

Question 28

What are 'stores' in the context of microservices?

Answer 28

Akin to a directory of resources - can only UPDATE or READ an entire store

Question 29

What are 'controllers' in the context of microservices?

Answer 29

Akin to a procedure, a client may ask the server to CREATE some change in the state of the world by executing a procedure

Question 30

What are the advantages of shared databases?

Answer 30

Rapid integration between different departments | Complete consistency of data between departments

Question 31

What are the disadvantages of shared databases?

Answer 31

Changes made to departments are slow or breaking | Database technology used by departments gets fixed

Question 32

What are the three ways to implement transactions in a database?

Answer 32

Try again later Abort the entire operation Distributed transactions

Question 33

What is the 'try again later' approach to transactions?

Answer 33

We accept that the eventual consistency will ensure the data is consistent in the end

Question 34

What is the 'abort the entire operation' approach to transactions?

Answer 34

Stop the entire operation - undo what has been done so far

Question 35

What is the 'distributed transactions' approach to transactions?

Answer 35

A transaction manager asks participants to perform a two-phase commit

Question 36

What is the CAP theorem?

Answer 36

Consistency - every read returns the result of the most recent write Availability - every node always performs a read or write Partition Tolerance - even if nodes become disconnected C and A are maintained You can only ever have two of these at once

Question 37

What are the most common patterns of communication between microservices?

Answer 37

Orchestration | Choreography

Question 38

What is the orchestration model of microservice communication?

Answer 38

Centralized controller tells each part of the system what it should be doing

Question 39

What is the choreography model of microservice communication?

Answer 39

One part of the system publishes an event to which others subscribe - like subscribing to an event listener

Question 40

What is a timeout?

Answer 40

A timeout is triggered when a downstream service fails to respond in time, allowing for alternative action

Question 41

What is a circuit breaker?

Answer 41

A CB is blown when a downstream service fails to respond in time or fails with an error Subsequent attempts to access the downstream service will immediately fail without tying up the resources that they otherwise would if they actually tried to access the service without the CB

Question 42

What is a bulkhead?

Answer 42

Closed when a downstream service fails to respond in time or fails with an error - perhaps by limiting the size of a connection pool Attempts to use downstream service either fail or switch to an alternative until bulkhead is open again

Question 43

What is vertical scaling?

Answer 43

Effectively buying more computing power - limited by moore's law

Question 44

What is horizontal scaling?

Answer 44

Adding more replicas - this is easy with services and avoids the limitations of moore's law

Question 45

What is load balancing?

Answer 45

Distributes requests to two or more replica machines that deliver the same service