Module 2b - Services & Microservices

Question 1

What is a service?

Answer 1

A service is a self-contained and reusable component that performs a specific task.

Ex: return price of a stock, append a message to a blog

Question 2

What is encapsulation with respect to services?

Answer 2

A service is encapsulated if it exposes an interface and hides its implementation

Question 3

What are Web Services?

Answer 3

Services that use web protocols (ex HTTP) for transport

Question 4

How are services accessed? As in how do they facilitate communication between other services?

Answer 4

Through communication protocols that may be layered on top of other protocols for transport

Question 5

What is a service-oriented architecture? (SOA)

Answer 5

An architecture where functionality is separated into a collection of services that can can be developed, deployed, and maintained independently

Question 6

Service-Oriented Architectures include middleware infrastructure. Why?

Answer 6

To facilitate integration of services

Question 7

What strategy do microservice-based architectures follow that service-oriented-architectures do not?

Answer 7

Microservice Architectures take the divide-and-conquer strategy of service-oriented-architectures and make it more loosely coupled and distributed

Question 8

Do Microservices rely on a common communication mechanism? Do they share data?

What benefits & drawbacks does this provide?

Answer 8

They don’t rely on a single method of communication, and they do not share data.

This improves fault tolerance but complicates coordination among components

Question 9

Are microservices are typically divided into small computing units. What is the benefit of this?

Answer 9

They become easy to develop, deploy, and maintain independently than larger components.

This also helps scalability

Question 10

What is SOAP?

Answer 10

Simple Object Access Protocol

Can only make HTTP POST requests

Question 11

What other protocol is SOAP layered on top of?

What does SOAP use for its message format?

Answer 11

SOAP is layered on top of HTTP

SOAP uses XML as its message format

Question 12

What is REST?

Answer 12

Representational State Transfer

A stateless model for interacting with HTTP

Question 13

What is the motivation behind using REST over SOAP

Answer 13

Simple Web services can be constructed by using HTTP protocol directly instead of layering another protocol on top of it (SOAP does that). SOAP only can make POST requests

REST is lighter weight than SOAP

Question 14

Does REST avoid layering another protocol on top of HTTP?

Answer 14

REST directly provides access to remote resources using HTTP methods such as GET, PUT, POST

REST is a model of interaction rather than a protocol

Question 15

What differentiates REST from SOAP?

Answer 15

• REST is not a protocol (SOAP is)
• SOAP can only make POST requests, REST can make all HTTP requests
• REST is stateless
• REST defines the format of messages (SOAP is only XML)
• REST can cache responses to GET requests, SOAP cannot

Question 16

How does caching work in REST vs SOAP?

Answer 16

REST can make HTTP GET requests. When such a response is returned, it can be cached using existing HTTP mechanisms.

SOAP transports requests using non-idempotent HTTP POST messages - SOAP can only make POST requests

Question 17

What are microservices?

Answer 17

Fine-grained, loosely-couples services which are isolatable and function independently of other microservices

Question 18

What 4 architectural styles do Service-Oriented-Architectures combine?

Answer 18

• Layered Architecture
• Object based Architecture
• Data centred Architecture
• Event based Architecture

Question 19

What are RESTful Architectures?

Answer 19

REST-based Web services. They are based on resource sharing

Question 20

What are the 4 key characteristics of RESTful architectures?

Answer 20

1. Resources are identified through a single naming scheme, namely URI (Universal Resource Identifiers)
2. All services offer the same interface, consisting of at most four operations (PUT, GET, DELETE, POST)
3. Messages sent to or from a service are fully self-described
4. After executing an operation at a service, that component forgets everything about the caller (stateless execution)

Question 21

What does stateless execution in REST mean?

Answer 21

HTTP is stateless meaning it does not explicitly keep track of users and sessions.

Question 22

What are Cookies and why do Applications use them?

Answer 22

Cookies are a form of persistent storage kept in the client for a resource request. They use cookies to maintain information about a REST API call and manage the state of the interaction

Question 23

Suppose a RESTful service calls an API to get an image from a gallery microservice. If the metadata returned is purely the image, would the API be able to retrieve the “next” image in the gallery?

Answer 23

It cannot. The REST API call does not maintain state or any additional metadata about the resource.

Question 24

What is JSON? whats is the use case with REST?

Answer 24

Java Script Object Notation.

Used in RESTful services to encode the API metadata

Question 25

What makes JSON scalable and more useful than XML?

Answer 25

JSON is compact and easy to parse (easier than XML). It also predefines all the datatypes that it encodes (number, string, boolean, array, object, null)

Question 26

How is JSON structured?

Answer 26

A collection of key-value pairs, keys must be strings. Values are any of: number, string, boolean, array, object or null