Chapter 5: Elastic Load Balancing, Amazon CloudWatch, and Auto Scaling

1. A, D. An Auto Scaling group must have a minimum size and a launch configuration defined in order to be created. Health checks and a desired capacity are optional.

• 创建as的时候必须指定mininum 和 创建launch configuration
• 健康检查和desired capacity都是可选项

2. B. The load balancer maintains two separate connections: one connection with the client and one connection with the Amazon EC2 instance.

• load balancer 一方面要接收client的请求，一方面要将请求转发到后端的ec2实例

3. D. Amazon CloudWatch metric data is kept for 2 weeks.

• cloudwatch 的指标数据可以保存两周，时间段为 60 秒 (1 分钟) 的数据点可用 15 天
• 最初以较短时间段发布的数据点汇总在一起，可实现长期存储。例如，如果您使用 1 分钟的时间段收集数据，数据以 1 分钟的精度保持 15 天可用。15 天之后，此数据仍可用，但汇总在一起，只能以 5 分钟的精度检索。63 天之后，数据进一步汇总，以 1 小时的精度提供。
• 自 2016 年 7 月 9 日起，CloudWatch 开始保留 5 分钟和 1 小时指标数据。

4. A. Only the launch configuration name, AMI, and instance type are needed to create an Auto Scaling launch configuration. Identifying a key pair, security group, and a block device mapping are optional elements for an Auto Scaling launch configuration.

• launch configuration必选：instance type、AMI、name
• launch configuration可选：key pair、SG、存储设置都是可选的；

5. B. You can use the Amazon CloudWatch Logs Agent installer on existing Amazon EC2 instances to install and configure the CloudWatch Logs Agent.

• CloudWatch Log Agent是用来进行日志采集监控的解决方案，不过需要自己安装

6. C. You configure your load balancer to accept incoming traffic by specifying one or more listeners.

• load balancer主要通过listener进行流量采集，不过AWS 的lb不支持udp协议

7. D. The default Amazon EC2 instance limit for all regions is 20.

• region的默认的EC2实例最大限制数目是20

8. A. An SSL certificate must specify the name of the website in either the subject name or listed as a value in the SAN extension of the certificate in order for connecting clients to not receive a warning.

• 通过创建一个ssl证书，指定website name，通过subject name值的扩展来规避警告。
• 不确定...

9. C. When Amazon EC2 instances fail the requisite number of consecutive health checks, the load balancer stops sending traffic to the Amazon EC2 instance.

• 将LB发现某个ec2实例无法通过健康检查，能做的就是不将流量转发过去。

10. D. Amazon CloudWatch metrics provide hypervisor visible metrics.

• CloudWatch的EC2基本指标如下：CPU、硬盘、网络

11. C. Auto Scaling is designed to scale out based on an event like increased traffic while being cost effective when not needed.

• 配置自动扩展组就行了，在每个用户访问的内容都不一样的情况下，不需要用cloudfront

12. B. Auto Scaling will provide high availability across three Availability Zones with three Amazon EC2 instances in each and keep capacity above the required minimum capacity, even in the event of an entire Availability Zone becoming unavailable.

• 高可用就是要在多个AZ，单个AZ不可用，其他AZ仍旧能保持65%的访问能力

13. B, E, F. Auto Scaling responds to changing conditions by adding or terminating instances, launches instances from an AMI specified in the launch configuration associated with the Auto Scaling group, and enforces a minimum number of instances in the min-size parameter of the Auto Scaling group.

• AS 会对依据条件进行扩展或者收缩；
• AS 必须先创建启动的配置文件；
• AS 中启动的实例必须大于mini-size 设定的值

14. D. A, B, and C are all true statements about launch configurations being loosely coupled and referenced by the Auto Scaling group instead of being part of the Auto Scaling group.
15. A, C. An Auto Scaling group may use On-Demand and Spot Instances. An Auto Scaling group may not use already stopped instances, instances running someplace other than AWS, and already running instances not started by the Auto Scaling group itself.

• 一个AS 组会使用on-demand实例和spot instance

16. A, F. Amazon CloudWatch has two plans: basic, which is free, and detailed, which has an additional cost. There is no ad hoc plan for Amazon CloudWatch.

• CloudWatch的base计划：5分钟，免费
• CloudWatch的detail计划：1分钟，收费

17. A, C, D. An Elastic Load Balancing health check may be a ping, a connection attempt, or a page that is checked.

• LB的健康检查主要是通过发送ping、网页请求、端口连接方式完成

18. B, C. When connection draining is enabled, the load balancer will stop sending requests to a deregistered or unhealthy instance and attempt to complete in-flight requests until a connection draining timeout period is reached, which is 300 seconds by default.

• 当instance的连接用尽，处于不健康的状态，LB会继续保持连接等待超时，同时不会发送新的流量过去。对于新的请求专向错误提示页面

19. B, E, F. Elastic Load Balancing supports Internet-facing, internal, and HTTPS load balancers.

• LB支持互联网、内网、HTTPS协议的负载均衡

20. B, D, E. Auto Scaling supports maintaining the current size of an Auto Scaling group using four plans: maintain current levels, manual scaling, scheduled scaling, and dynamic scaling.

• AS 支持 手工扩展、动态扩展、定时扩展的等策略

知识点总结

• Understand what the Elastic Load Balancing service provides. Elastic Load Balancing is a highly available service that distributes traffic across Amazon EC2 instances and includes options that provide flexibility and control of incoming requests to Amazon EC2 instances.

• 了解什么是ELB 服务。ELB服务是一个高可用的跨EC2的流量分发服务，为EC2提供了自有的流量请求；

• Know the types of load balancers the Elastic Load Balancing service provides and when to use each one. An Internet-facing load balancer is, as the name implies, a load balancer that takes requests from clients over the Internet and distributes them to Amazon EC2 instances that are registered with the load balancer. An internal load balancer is used to route traffic to your Amazon EC2 instances in VPCs with private subnets.
  An HTTPS load balancer is used when you want to encrypt data between your load balancer and the clients that initiate HTTPS sessions and for connections between your load balancer and your back-end instances.

• 了解各种LB类型以及如何去使用。一个面向互联网的LB是从互联网获取流量，同时将流量分发到后端注册到LB上的EC2实例。一个内部的LB被用来做VPC内私有子网的流量转发。一个HTTPS LB被用来做client到LB的数据加密，用于初始化HTTPS ，同时用来做LB与后端instance的连接；

• Know the types of listeners the Elastic Load Balancing service provides and the use case and requirements for using each one. A listener is a process that checks for connection requests. It is configured with a protocol and a port for front-end (client to load balancer) connections and a protocol and a port for back-end (load balancer to back-end instance) connections.

• 了解ELB服务提供的各种监听器以及应用场景 。一个listener是一个连接的处理流程。被用来配置协议和前端端口，同时设置后端连接的处理协议与端口；

• Understand the configuration options for Elastic Load Balancing. Elastic Load Balancing allows you to configure many aspects of the load balancer, including idle connection timeout, cross-zone load balancing, connection draining, proxy protocol, sticky sessions, and health checks.

• 了解ELB的配置选项。ELB允许我们的配置多个特性，包括connection timeout，跨区LB，链接消耗数，代理协议，会话保持及健康检查；

• Know what an Elastic Load Balancing health check is and why it is important. Elastic Load Balancing supports health checks to test the status of the Amazon EC2 instances behind an Elastic Load Balancing load balancer.

• 了解ELB的健康检查为嘛很重要。ELB支持针对注册到ELB上的EC2的健康检查；

• Understand what the amazon CloudWatch service provides and what use cases there are for using it. Amazon CloudWatch is a service that you can use to monitor your AWS resources and your applications in real time. With Amazon CloudWatch, you can collect and track metrics, create alarms that send notifications, and make changes to the resources being monitored based on rules you define. For example, you might choose to monitor CPU utilization to decide when to add or remove Amazon EC2 instances in an application tier. Or, if a particular application-specific metric that is not visible to AWS is the best indicator for assessing your scaling needs, you can perform a PUT request to push that metric into Amazon CloudWatch. You can then use this custom metric to manage capacity.

• 了解什么是CloudWatch服务及使用场景。CloudWatch是一个能实时监控AWS resources和你的application的服务。通过CloudWatch，你可以搜集和跟踪指标，创建警报同时发送通知，基于当你定义的监控规则适时作出改变；例如，你也许选择监控CPU利用率来决定是否增加或者减少EC2 instances在应用层。或者一个特定的应用指标来决定是否有扩展需求，你可以put一个请求同时将指标放到CloudWatch，然后你能用这个定制的指标管理容量；

• Know the differences between the two types of monitoring—basic and detailed— for Amazon CloudWatch. Amazon CloudWatch offers basic or detailed monitoring for supported AWS products. Basic monitoring sends data points to Amazon CloudWatch every five minutes for a limited number of preselected metrics at no charge. Detailed monitoring sends data points to Amazon CloudWatch every minute and allows data aggregation for an additional charge. If you want to use detailed monitoring, you must enable it—basic is the default.

• 了解两种类型的监控“basic和detail”对于CloudWatch的不同。CloudWatch提供了basic或者detail监控用于AWS产品。Basic监控将数据每隔5分钟发送一定数量预先选择好的指标，同时不产生费用。Detailed 监控是每隔1分钟发送数据到CloudWatch，需要付额外的费用。如果你想详细监控，你必须启动它，默认是basic。

• Understand Auto Scaling and why it is an important advantage of the AWS Cloud. A distinct advantage of deploying applications to the cloud is the ability to launch and then release servers in response to variable workloads. Provisioning servers on demand and then releasing them when they are no longer needed can provide significant cost savings for workloads that are not steady state.

• 了解AS，并且知道他对于AWS cloud的重要性；云的最大优势是可以基于workload的变化来相应的调整部署应用的而数量。按需的获取servers，同时在不需要的时候实时释放他们，可以有效的降低成本。

• Know when and why to use Auto Scaling. Auto Scaling is a service that allows you to scale your Amazon EC2 capacity automatically by scaling out and scaling in according to criteria that you define. With Auto Scaling, you can ensure that the number of running Amazon EC2 instances increases during demand spikes or peak demand periods to maintain application performance and decreases automatically during demand lulls or troughs to minimize costs.

• 了解when and why 去使用AS。AS是一个允许你按照自己定义的规则自动扩展和收缩EC2数量的服务。通过AS，你可以保证一定数量的EC2实例在流量峰值的时候按需增加，来保证应用的性能。同时在峰值过后自动的减少以降低成本；

• Know the supported Auto Scaling plans. Auto Scaling has several schemes or plans that you can use to control how you want Auto Scaling to perform. The Auto Scaling plans are named Maintain Current Instant Levels, Manual Scaling, Scheduled Scaling, and Dynamic Scaling.

• 了解AS支持的计划。AS有多个策略你可以用来做弹性伸缩。AS策略被命名如下：Maintain Current Instance Levels，Manual Scaling、Scheduled Scaling、Dynamic Scaling

• Understand how to build an Auto Scaling launch configuration and an Auto Scaling group and what each is used for. A launch configuration is the template that Auto Scaling uses to create new instances and is composed of the configuration name, AMI, Amazon EC2 instance type, security group, and instance key pair.

• 理解如何构建一个AS 配置和一个AS 扩展组。一个启动配置模板是用来构建新的instance，需要指定如下属性：名称、AMI、instance type，安全组，instance key pair。

• Know what a scaling policy is and what use cases to use it for. A scaling policy is used by Auto Scaling with CloudWatch alarms to determine when your Auto Scaling group should scale out or scale in. Each CloudWatch alarm watches a single metric and sends messages to Auto Scaling when the metric breaches a threshold that you specify in your policy.

• 了解AS的策略及其应用场景。一个伸缩策略结合CloudWatch警报来决定你什么时间来自动的伸缩或者缩小扩展组。每个CloudWatch alarm观察一个单一的指标来发送消息到AS，当指标值突破了策略中设定的阀值；

• Understand how Elastic Load Balancing, amazon CloudWatch, and Auto Scaling are used together to provide dynamic scaling. Elastic Load Balancing, Amazon CloudWatch, and Auto Scaling can be used together to create a highly available application with a resilient architecture on AWS.

• 理解如何将ELB、CloudWatch和AS结合到一起来提供动态的扩展。他们可以在AWS上创建一个高可用的应用架构；