Quiz 1 Flashcards
What is a SLA or Service Level Agreements?
A contract between a service provider and an end user
What are the two key issues of Service Level Agreements?
Who will monitor an SLA violation and what will be the ramification of a SLA violation?
What are the two important criteria SLA’s in clouds?
The availability SLA and the performance SLA
What is the availability metric in SLAs?
What percentage the service will be up for
What typically occurs if a SLA does not meet the required availability metric?
A credit percentage is given to the user
What is the problem around the Performance SLA?
It is difficult to define the performance of a user service
What are the four key characteristics of cloud services?
On-Demand
Shared Resource Pool
Resource Elasticity
Metered Service
What is the Resource Elasticity characteristic?
Grid/Internet computing supported limited resource elasticity
What are the 4 cloud service models?
Infrastructure as a Service
Platform as a Service
Software as a Service
Everything as a Service (Xaas)
What is Infrastructure as a Service
Providing on demand virtual infrastructures to cloud users
Like Virtual Machines, Storage or networks
What is Platform as a Service?
A cloud service model that provides the development, testing, debugging and deploying of applications
What are some issues with Platform as a Service?
You have limited control over the configs for infrastructure and software stacks, there is a learning curve to use of the platform, there is an ease of transition to the cloud, and there is the issue of platform reliability
What is Software as a Service?
On-demand web services/apps
What is a public cloud?
A public cloud is a cloud that anyone can use as a pay as you go cost
What is a private cloud?
Private clouds are clouds that are used exclusively by a single organization
What is a hybrid cloud?
A mixture of private and public clouds
What is cloud bursting?
Managing a large burst of requests by using the public cloud
What is provided by infrastructure as a service?
On demand virtual infrastructure, things like VMs, storage, network, containers ect.
What is the users’ role in IaaS?
Managing their instances/resources and things on the servers
What is an AWS instance?
A virtual machine hosted on the amazon web service
What is an elastic IP?
A static public IP address allocated to an instance
An elastic IP address not released when the instance is stopped or terminated
What is EC2? (Elastic Compute Cloud)
A web service for launching instances of an application under several operating systems
What characterizes an EC2 instance?
The resources it provides
What are the three consumption models of a EC2?
The On Demand Instance
The Reserved Instance
The Spot Instance
What is the On Demand Instance?
It is the pay as you go type of consumption model. It is the most expensive but also the most common
What is the Reserved Instance?
Reserving a number of instances for use on a server. It has a percentage discount on the price but requires a longer term usage
What is a spot instance?
Using space EC2 resources, has a large discount but very low availability
What is another name for a spot instance?
Transient instance model
How can spot instance lifetimes can be measured?
Analyzing spot market price changes
What are some Pros For IaaS?
High Flexibility: full control over VMs
Users can run anything they want
Similar to Server/On-Prem (Easy to move)
What are some Cons for IaaS?
There is alot of management that needs to be done
Can be expensive
Scaling and Scalability are users responsibility
No control over physical host machine/infrastructure
What are some Pros of PaaS?
Easy to dev, test and deploy simple web apps
No worry about infrastructure
Cheaper than IaaS
What are some Cons of PaaS?
No control over the Supported Language, Framework or Support Services, there is a great need for the Dev’s experience with the usage of the app and there is a large learning curve
What are some Pros of SaaS?
No installation and no maintenance
Global accessibility of the app and data
Often have better functionality
What are some Cons of SaaS?
No control over the system/infrastructure
Questions over the security and privacy as the company has control over both these two factors
What are the objectives of SLA?
Identify and define the customer’s needs and constraints
Provide a framework for providing a clear def of services, costs and ramification of a violation of the terms of agreement
Simplify complex issues
Eliminate unrealistic expectations
What is Availiability?
The degree to which data or systems are accessible and in functioning condition
What are the three causes of availability failure?
Failure by human error, infrastructure failure, natural disaster and other failure
What are the 7 types of availability?
Data availability, network availability, system availability, communication availability, power availability, people availability, other resource availability
How do you achieve high data availability?
By backing up your software
What are the three backup methods?
Full backup
Differential Backup
Incremental Backup
What is Full Backup?
Backing up all files/data
What is Differential Backup?
Backing up files that have been created or modified only since the last full backup
What is Incremental Backup?
Backing up files that have been created of modified only since the last backup?
What are the Pros and Cons of a Full Backup?
Pros: Complete Copy of data, Simple and Easy to Manage
Cons: Storage is high, Time Consuming
What are the Pros and Cons of a Differential Backup?
Pros: Faster than a full backup, Need less storage than a full backup
Cons: Slower than an incr. backup and has an issue of redundancy (potentially many unneeded copies of the same data)
What is the Pros and Cons of Incremental Backups?
Pros: Only backup for a change, Fastest, least storage space
Cons: Management overhead, Complicated recovery process
What are some ways to avoid Single Point of Failure?
Server redundancy, Hardware component redundancy, Storage redundancy, Network redundancy, Redundant Power, A/C cooling, Monitoring and failover mechanisms
What is the Mean Time Between Failures? (MTBF)
The amount of time between failures
What is the Mean Time to Recover/Repair? MTTR
The amount of time required to repair a failed system
How do you calculate Availability?
MTBF/(MTBF+MTTR)
What is a Con of Public Clouds?
You have less control of the infrastructure (host machine, physical security and physical network)
What are the three use cases of hybrid clouds?
Cloud Bursting
Backup/Recovery
Load Balancing/Access Distribution
What are some Key Challenges for Cloud Bursting?
VM Migration, API Support
What are some Key Issues with Backup/Recovery for Hybrid Clouds?
Privacy and Compliance
What is Load Balancing/Access Distribution?
Deploying apps in the public cloud to improve end user experiences
What are the Pros and Cons of a Public Cloud?
Pros: Scalability, No maintenance, Lower $$$, Security
Cons: No control over infrastructure, No flexibility, Compliance (Legal)
What are the Pros and Cons of a Private Cloud?
Pros: Feel more “secure”, Flexibility, Customizability, Control over Compliance
Cons: Cost, Scalability, Users think it is free
What are the Pros and Cons of Hybrid Clouds?
Pros: Both
Cons: Both
What are they ways that AWS security is better than any particular company?
Physical Security, Economics of scale, AWS security people only doing security, VM OSes are patched, Good default security
What is Backup/Recovery for Hybrid Clouds?
Backing up data into public cloud to reduce private cloud’s CAPEX
What is Elasticity?
Degree to which a system is able to adapt to workload change by provisioning and de-provisioning resources in an automatic manner
What is Scalability?
The ability of a system to manage increasing workloads by making use of additional resources
What is Amdahl’s Law?
How fast something can be speed up is limited by the part that cannot be sped up or Max Speedup = 1(1-P) where P is the parallel Part Duration.
What is Amdahl’s Law when you do not have unlimited resources?
1/(1-P) + (P/K) where P is the parallel part and K is the processors
What is IaaS Elasticity?
Adding/Removing virtual machines
Increases/Decreasing CPU, memory, storage capacity by adding/removing additional virtual hardware components to existing machines
What is Horizontal Scaling?
Changing the number of resources (quanatiy)
What is Vertical Scaling?
Changing the resource specification (quality)
What are the pros and cons of Horizontal Scaling?
Pro: Unlimited Scalability, Common to Do
Scaling Delay
Cons: Coarse grained, Must support distributed/parallel architecture
What are the pros and cons of Vertical scaling?
Pro: Finer-grained, SW License Cost, No Distributed/Parallel Architecture
Con: Easily reach to max, Live Migration, Imperfect technique, Single Point of Failure
What is Under Provisioning?
Not having enough resources to meet demand
What is Over Provisioining?
Having too many resources to meet demand
What is Autoscaling?
Rule-based resource scaling mechanism
What are some things Autoscaling scales based on?
Monitoring resource status and application metrics
Determining when to add/release computing resources
Determining how much computing resources to be added/released
What are the two operations involved in AWS autoscaling?
Scaling Out (Better QoS) Done for high demand
Scaling In (Cost Efficiency) Done for Low Demand
What is the advantages of Autoscaling?
Improved QoS, Saving Money
What is some limitation on autoscaling?
VM startup time and system monitoring
Where is the bottleneck in scaling?
Transferring the VM image to the server
What are the pros and cons of autoscaling?
Pros: Simple and easy to achieve high availability, fault tolerance, and scalability, Better Qos, and cost efficiency
Cons: Reactive System, Scaling Delay, Unclear relationship between system metrics and Qos
What are some issues with Predictive Autoscaling?
All workload patterns are not necessarily predictable
Creating accurate predictors is hard
Dealing with unpredictable events
Can over-provision by mispredictions
