Wk 3 Storage

Question 1

Microservice bus function:

Answer 1

Connects microservices together with an open pluggable framework.

Instead of all services having a different protocol you have a common protocol “Bus”.

Question 2

Microservice bus Characteristics :

Answer 2

It has a single:
- communication protocol
- Data format
- Interface convention

Ex:
Http
Json
Rest

Question 3

Http:

Answer 3

Synchronous protocol.
Client sends a request and then blocks the channel until it receives a response form the server.

It is well understood, widely implemented and trusted

Question 4

Http request sections:

Answer 4

• Request Line
• Headers
• Body ( optional)

Question 5

Rest

Answer 5

Representational state transfer. ( Way to standardize APIs)

Question 6

What are a the resources provided by microservices:

Answer 6

Resources are formed by combining smaller resources.

Not all resources fit together.

Question 7

Resources archetypes:

Answer 7

• Documents
• Collection
• Store
• Controller

Question 8

Documents:

Answer 8

Describe operations on files like resources.

Ex GET PUT DELETE

Question 9

Collection:

Answer 9

Operations on directory like resources.

The server chooses the name of the resources.

Ex
Get reads directory
Post create new resource in the directory

Question 10

Store:

Answer 10

Collection of objects.

Each item in the store is named differently.

Operations are directory like but the user decides the object name.

Question 11

Controller:

Answer 11

Describes impossibile operations on external resources.

Posts causes the external resource to carry out some task and returns any result.

Question 12

Google remote procedure call

Answer 12

Services connected through grpc are defined using protocol buffers (type safety) and binary data ( for efficient transfer)

Question 13

How does grpc work:

Answer 13

You agree between two services a binary format that you are going to exchange there after you use your binary encoding.

Question 14

Benefit or grpc

Answer 14

7 times faster than REST when recieving data and 10 times faster when sending.

( No need to change the data to JSON)

Question 15

An enterprise computer system may store data using:

Answer 15

• centralised database
• distributed database

Question 16

Centralised database / monolith database andvantages:

Answer 16

• easier
• ensures accuracy
• consistency of data is maintained
• completeness

Question 17

Disadvantages of centralised databases:

Answer 17

Everything is coupled so you need an agreement from all departments to effect a change.

Question 18

Centralised database transactions:

Answer 18

• Commit ( completes successfully) database is moved to a new consistent state

-Aborts ( completes unsuccessfully) the database is restored to a previous consistent state

Question 19

ACID properties of a transaction:

Answer 19

• Atomicity
• Consistency
• Isolation
• Durability

Question 20

Atomicity

Answer 20

Something either happens or it donts

Question 21

Consistency

Answer 21

No transaction is half done

Question 22

Isolation

Answer 22

One transaction can’t see the actions of another, doesn’t matter the order

Question 23

Durability

Answer 23

If a transaction happens, it succeeds even if the system fails ( need to check this is correct)

Question 24

Distributed database

Answer 24

Consists of a series of databases each assigned to a series of individual microservice.

Question 25

Disadvantages of distributed databases:

Answer 25

Difficult to ensure accuracy, completeness and consistency.

Question 26

Advantages distributed systems:

Answer 26

A database for each service enables independence in development.

Question 27

Distributed transactions:

Answer 27

- Two phase commit - sagas

Question 28

Two phase commit:

Answer 28

A transaction coordinator asks a number of participant transactions to vote whether they are prepared to commit a change. Each participant holds locks on its data involved in the transaction until the coordinator decides to commit or abort.

Question 29

Issues with two phase commits:

Answer 29

- centralised coordinator - while everyone is voting all databases are locked waiting for the coordinator to decide

Question 30

Sagas

Answer 30

A coordinator transaction asks each participant to commit or abort a sequence. The data involved in the transaction is locked only until it decides to commit or abort. If all participants commit then everything is good otherwise the sequence ends and a compensating transaction is made to undo the work of those that have committed.

Question 31

Sagas what do they sacrifice?

Answer 31

Atomicity and rely on consistency

Question 32

Brewers convention:

Answer 32

You can't have availability, consistency and partition tollerance all the the same time.

Question 33

CAP theorem

Answer 33

There are 3 fundamental guarantees

Question 34

Availability

Answer 34

Response is received from every node ( Always access)

Question 35

Consistency

Answer 35

The same response is received from every node

Question 36

Partition Tollerance

Answer 36

The system works even if it becomes disconnected

Question 37

CP example

Answer 37

Banks even if there is a network failure they stay consistent

Question 38

CA

Answer 38

Unable to tollerate a system failure, you cant have a network ( ex. mainframe )

Question 39

How to decompose a database ?

Answer 39

- database then code - code then database - code and database

Question 40

Database then code decomposition:

Answer 40

Split the database first then split the code. No short term benefit Cost atomisation

Question 41

Code then database

Answer 41

Split the code first as it's easier to revoke. Short term benefits Confidence to complete the decomposition

Question 42

Code and database

Answer 42

Split the code and database as the same time No benefits, more work all at once

Question 43

Ap

Answer 43

Drops consistency sometimes.

Question 44

Why would a cloud provider be dissatisfied with the use of JSON communication for documents

Answer 44

- overhead JSON imposes on binary data - additional overhead processing -additional storage overhead From encoding and decoding binary using base64. Provider use a custom binary format such as gRPC avoids processing and storing overheads , sacrifice flexibility

Question 45

Problems of using a centralised database for microservices:

Answer 45

The database is distributed across many services: - duplication : multiple copies of data - consistency : copies up to date - security : must have controls everywhere - transaction management : must have ACID properties

Question 46

Ap for microservices:

Answer 46

- partition tolerant( available even if there is a network partition) - may have some inconsistency issues

Question 47

Improve communication between microservices :

Answer 47

- standard protocol REST small set of common operations - http : handles client server networking - standard data format XML JSON easily processed and extended - Remote procedure call grpc automatically generates networking code