今年能順利通過AWS Solutions Architect Professional考試阐污，分享給我練習題的好哥們兒功不可沒玄柠。（詳情可參閱2019 AWS解決方案架構師專業(yè)級Solutions Architect Professional考試回顧）征得他的同意之后突梦，我試著把其中一些題目和解題思路也記錄一二。一來讓自己有繼續(xù)溫故知新的動力羽利，二來也希望能為其他準備AWS SAP考試的朋友提供些許參考宫患。
由于AWS SAP考試均為場景題，選項中可能存在多個方案都可行这弧，但需要選擇一個最優(yōu)解的情形撮奏。我會盡量針對每一個選項進行分析俏讹，比較各自的優(yōu)劣。當然畜吊，我個人水平有限泽疆，解析題目時疏漏之處在所難免，還請各位海涵玲献。
廢話少說殉疼，首次嘗試題目如下：
A company runs a legacy system on a single m4.2xlarge Amazon EC2 instance with Amazon EBS storage. The EC2 instance runs both the web server and a self-managed Oracle database. A snapshot is made of the EBS volume every 12 hours, and an AMI was created from the fully configured EC2 instance. A recent event that terminated the EC2 instance led to several hours of downtime. The application was successfully launched from the AMI, but the age of the EBS snapshot and the repair of the database resulted in the loss of 8 hours of data. The system was also down for 4 hours while the Systems Operators manually performed these processes. What architectural changes will minimize downtime and reduce the chance of lost data?
A. Create an Amazon CloudWatch alarm to automatically recover the instance. Create a script that will check and repair the database upon reboot. Subscribe the Operations team to the Amazon SNS message generated by the CloudWatch alarm.
B. Run the application on m4.xlarge EC2 instances behind an Elastic Load Balancer/Application Load Balancer. Run the EC2 instances in an Auto Scaling group across multiple Availability Zones with a minimum instance count of two. Migrate the database to an Amazon RDS Oracle Multi-AZ DB instance.
C. Run the application on m4.2xlarge EC2 instances behind an Elastic Load Balancer/Application Load Balancer. Run the EC2 instances in an Auto Scaling group access multiple Availability Zones with a minimum instance count of one. Migrate the database to an Amazon RDS Oracle Multi-AZ DB instance.
D. Increase the web server instance count to two m4.xlarge instances and use Amazon Route 53 round- robin load balancing to spread the load. Enable Route 53 health checks on the web servers. Migrate the database to an Amazon RDS Oracle Multi-AZ DB instance.
答案：B
題目難度：低
題目解析：題干中場景涉及的AWS服務包括EC2，EBS和AMI捌年，描述問題的關鍵字句已用黑體標出——在單一EC2實例上運行Web服務和用戶自主管理的數(shù)據庫瓢娜，實例意外關閉且EBS快照間隔時間為12小時，導致系統(tǒng)恢復后礼预，出現(xiàn)8小時的數(shù)據丟失眠砾。
因此，欲使系統(tǒng)停機時間降到最低托酸，并減少數(shù)據丟失褒颈，應解決單一實例引起的單點故障，同時優(yōu)化數(shù)據庫數(shù)據備份機制励堡。
我們來看看每一個選項谷丸。
選項A，引入Amazon CloudWatch報警和SNS消息服務及時通知用戶系統(tǒng)出現(xiàn)故障应结，但沒有任何措施用以降低系統(tǒng)停機時間或優(yōu)化數(shù)據庫備份機制刨疼，不能滿足題目要求。
選項B鹅龄，創(chuàng)建包含至少2個EC2實例的Auto Scaling group揩慕，并在EC2實例前端配置ELB/ALB，提升EC2實例的可用性和可靠性扮休。將用戶自主管理的Oracle數(shù)據庫遷移至Amazon RDS多可用區(qū)實例托管起來漩绵，可有效解決EBS快照備份數(shù)據的先天不足。該方案可行肛炮。
選項C止吐，除Auto Scaling group最低時只有1個EC2實例外，其余部分與選項B方案相同侨糟。該方案理論上也可行碍扔，但系統(tǒng)停機時間指標明顯不如擁有2個EC2實例的選項B，因此排除秕重。
選項D不同，將Web服務部署在2個EC2實例上，使用Route 53 round-robin均衡Web服務器的訪問請求，同時托管數(shù)據庫二拐。此方案僅能在2臺EC2實例間分配網絡訪問負載服鹅，無法完成Web服務的應用負載均衡。若Web服務器負載量出現(xiàn)激增百新，該方案不如選項B方案完善企软。
綜上所述，選項B應為最優(yōu)解饭望。
