Self-Adapting

Question 1

Why do we need adaptation?

Answer 1

Systems are often subject to various types of uncertainties:

• Changing conditions in the environment (resources, services,…)
• User behavior that is difficult to predict
• Goals may change dynamically

Uncertainties affect qualities (performance, reliability, efficiency, …)
Uncertainties difficult to anticipate before deployment

Question 2

What are the external factors?

Answer 2

Self-adapting systems handle uncertainty in:

• Its own status -> Example: disk throughput is lower than usual
• The environment -> Example: user requests have increase 10x
• Goals -> Example: request latency should be below 10ms from 20ms

Question 3

What are the internal factors?

Answer 3

1. Domain concerns:
   
   • Concerned with the goals for which the system is built
   • Example: database should serve 99% of requests under 50ms
2. Adaptation concerns:
   
   • Concerned about how the system realizes its goals under changing conditions. Maintain domain under control.
   • Example: database has configuration parameters to optimize performance for different workloads

Question 4

What are the 4 main Autonomic Computing Principles?

Answer 4

Self-configuring
Self-healing
Self-optimizing
Self-protecting

Question 5

Which system handles the domain concerns?

Answer 5

Managed system. The controllable software.

Question 6

Which system handles the adaptation concerns?

Answer 6

Managing system

Question 7

What are the domain concerns?

Answer 7

One of the internal factors which interacts with the environment and is concerned with the goals for which the system is built
Example: database should serve 99% of requests under 50ms

Question 8

What are the adaptation concerns?

Answer 8

One of the internal factors which interacts with the managed system and is concerned with how the system realizes its goals under changing conditions.
Example: database has configuration parameters to optimize performance for different workloads

Question 9

What are the components of the autonomic manager reference model MAPE-K?

Answer 9

Monitor
Analyse
Plan
Execute
Knowledge

Question 10

Define the self-configuring autonomic computing principle

Answer 10

Automatic integration and distribution of resources by the system in accordance with the high-level policies which state what is desired, not how to do it.

Question 11

Define the self-healing autonomic computing principle

Answer 11

Detection, diagnosis and reaction to system disruptions
– Faults in components of the system should not lead to failures
– Continuously analyze information from monitors and log files
– Key properties of dependable systems

Question 12

Define the self-optimizing autonomic computing principle

Answer 12

Automatically measure and tune resources to improve performance and usage. Systems have hundreds of tunable parameters.

Question 13

Define the self-protecting autonomic computing principle

Answer 13

Anticipate, detect, identify and protect against attacks. Known and unknown threats. Anticipate and prevent a system from reaching a faulty state.

Question 14

How to make a legacy system self-adapting?

Answer 14

Add feedback loops to deal with adaptation concerns

Question 15

How to make a new system self-adapting?

Answer 15

Separate domain concerns from adaptation concerns

More flexibility to handle future changes

Question 16

What are sensors?

Answer 16

Collect and measure metrics about:

• The system
• The environment
• The user of the system

Question 17

What are effectors or actuators?

Answer 17

Acts upon the system changing one or more of its parameters, examples:

• Modify a system configuration
• Add more replicas

Question 18

What are effectors or actuators?

Answer 18

Acts upon the system changing one or more of its parameters, examples:

• Modify a system configuration
• Add more replicas

Question 19

In the MAPE-K framework, what is the role of the Monitor stage?

Answer 19

Collect data from managed element and its execution context to update the Knowledge
Relies on the sensors for the different aspects of the system, environment and user

Question 20

In the MAPE-K framework, what is the role of the Plan stage?

Answer 20

Adapting the system impacts the system itself and executing the adaptation actions right away might not be a good idea.

Plan places restrictions on how fast the systems can adapt.

Plan prevents disruptions in the system caused by the adaptation itself, takes into account:

• Time taken to adapt
• Resource usage of existing replicas due to state transfer when adding new replicas

Question 21

In the MAPE-K framework, what is the role of the Analyse stage?

Answer 21

Determines whether adaptation actions are required

Decision is based on the monitor data and administrator goals found in the Knowledge

Question 22

In the MAPE-K framework, what is the role of the Execute stage?

Answer 22

Executes the adaptation actions of the generated plan, adapting the managed element.

Leverages the effectors.

Question 23

In the MAPE-K framework, what is the role of the Knowledge stage?

Answer 23

Abstraction of relevant data:
- The managed element
- The environment
- The administrator’s goals
Encodes the desired high-level policies and target Service Level Objectives and Service Level Agreement.

Question 24

What are Service Level Objectives (SLO)?

Answer 24

Specific target for a metric

Example: latency of request X should be below 50ms

Question 25

What is a Service Level Agreement (SLA)?

Answer 25

Formal (contractual) commitment made to a customer

Example: if SLO X is violated for more than 1s per day then reimburse customer