Lecture 6: QoS

Question 1

Resiliency Patterns

Answer 1

• Retry Pattern
• Circuit Breaker
• Rate Limiter

Question 2

Security Pattern

Answer 2

• Accès Token (OAuth)

- API Gateway can serve as intermediary between authorisation server and client

Question 3

Retry Pattern

Answer 3

• Provide acceptable level of service in the pace of failures
• Transient failures (short-time) (e.g., slow network connection)
• Retry after delay

Question 4

Circuit Breaker

Answer 4

• Long lasting failures
• Prevent application from performing an operation that is likely to fail
• Fail immediately (after threshold is reached)

Question 5

Circuit Breaker States

Answer 5

• Closed -> request will be forwarded
• Open -> Happens after threshold
• Half-open -> Happens after time-out -> call will be made to check if the service is available or not

Question 6

Rate Limiter

Answer 6

• # of requests that are allowed for a given period period of time
• Otherwise HTTP 429 too many requests
• API Gateway

Question 7

Scalability Model

Answer 7

X-axis (run multiple copies)
Y-axis (break down monolithic application)
Z-axis (partition and distribute data)

Question 8

X-axis scaling

Answer 8

• Similar to computer cluttering (Spark Cluster)
• Leveraging cloning of Microservices
• Load Balancer

Question 9

Y-axis scaling

Answer 9

• API Gateway

- Content-based Routing

Question 10

Z-axis scaling

Answer 10

• Database sharding (each shard holds a subset of the data)

- Content-based routing (e.g., split us and eu data)

Question 11

Caching Pattern

Answer 11

• Reduce the frequency of expensive operations such as reading data from database
• We first look at the data in the cache and then serve the request -> Cache hit
• If the data is not in the cache, then we pick the data from the actual target such as database and then store the retrieved data in cache
• At the API Gateway