単一のEC2インスタンスのSLAが 90% から 99.5% に変更されました

単一のEC2インスタンスのSLAが 90% から 99.5% に変更されました。なお、「SLA 99.5% = 99.5% 以上必ず停止しない」という保証ではないので要注意です。SLAを満たさない場合は利用費に応じたサービスクレジットが返還されるだけなので、障害発生時のビジネスインパクトが大きいシステムはMulti-AZ構成にするなど可用性を高める対応が必要です。
2021.09.15

単一のEC2インスタンスのSLAが 90% から 99.5% に変更されました

こんにちは、のんピ(@non____97)です。

タイトルの通り、単一のEC2インスタンスのSLAが 90% から 99.5% に変更されました。

Instance-Level SLA

For each individual Amazon EC2 instance (“Single EC2 Instance”), AWS will use commercially reasonable efforts to make the Single EC2 Instance available with an Instance-Level Uptime Percentage of at least 99.5%, in each case during any monthly billing cycle (the “Instance-Level SLA”). In the event any Single EC2 Instance does not meet the Instance-Level SLA, you will be eligible to receive a Service Credit as described below.

Amazon Compute Service Level Agreement

これは激アツですよね。

SLAで定義されている月間稼働率を下回る場合には、利用費に対する割合のサービスクレジットの返還が可能です。

単一のEC2インスタンスの場合、月間稼働率毎の返還されるサービスクレジットの割合は以下の通りです。

月間稼働率 返還されるサービスクレジットの割合
99.5% 未満、99.0% 以上 10%
99.0% 未満、95.0% 以上 30%
95.0% 未満 100%

ちなみに、Multi-AZ構成のEC2インスタンスのSLAは 99.99% です。

Region-Level SLA

For Included Services with all running instances or tasks deployed concurrently across two or more AZs in the same region (or at least two regions if there’s only one AZ in a given region), AWS will use commercially reasonable efforts to make each Included Service available for each AWS region with a Monthly Uptime Percentage of at least 99.99%, in each case during any monthly billing cycle (the “Region-Level SLA”). In the event any of the Included Services do not meet the Region-Level SLA, you will be eligible to receive a Service Credit as described below.

Amazon Compute Service Level Agreement

月間稼働率の計算方法

じゃあ、月間稼働率ってどうやって計算するの?」という声が上がってきそうなので、SLAの定義を確認します。

SLA Definitions

  • “Availability Zone” and “AZ” mean an isolated location within an AWS region identified by a letter identifier following the AWS region code (e.g., us-west-1a).
  • “Monthly Uptime Percentage” is calculated by subtracting from 100% the percentage of minutes during the month in which any of the Included Services, as applicable, was in the state of Unavailability.
  • “Instance-Level Uptime Percentage” is calculated by subtracting from 100% the percentage of minutes during the month in which a Single EC2 Instance was in the state of Unavailability.
  • A “Service Credit” is a dollar credit, calculated as set forth above, that we may credit back to an eligible account.
  • “Unavailable” and “Unavailability” mean:
    • For the Instance-Level SLA, your Single EC2 Instance has no external connectivity.
    • For the Region-Level SLA applicable to Amazon EC2 (other than Single EC2 Instances), Amazon ECS, or AWS Fargate, when all of your running instances or running tasks, as applicable, deployed in two or more AZs in the same AWS region (or, if there is only one AZ in the AWS region, that AZ and an AZ in another AWS region) concurrently have no external connectivity.
    • For the Region-Level SLA applicable to Amazon EBS, when all of your attached volumes deployed in two or more AZs in the same AWS region (or, if there is only one AZ in the AWS region, that AZ and an AZ in another AWS region) perform zero read write IO, with pending IO in the queue.

Amazon Compute Service Level Agreement - SLA Definitions

月間稼働率は、ひと月のうち、単一のEC2インスタンスが使用不可(外部と接続できない)の状態にあった分数の割合を100%から差し引いて算出するようですね。

サービスクレジットの返還の手続き

SLAで定義されている月間稼働率を下回り、サービスクレジットの返還の手続きを行う場合の手続きも確認します。

手続きの流れは、以下のように利用者がサポートチケットを作成して、月間稼働率を下回った事の証拠となるエビデンスの提出が必要となります。

Credit Request and Payment Procedures

To receive a Service Credit, you must submit a claim by opening a case in the AWS Support Center. You may only submit a claim under either the Region-Level SLA or the Instance-Level SLA, as these claims cannot be combined or stacked for a particular Single EC2 Instance. Your credit request must be received by us by the end of the second billing cycle after which the incident occurred and must include the information specified below for the Region-Level SLA and Instance-Level SLA, respectively.

Region-Level SLA requests must include:

  1. the words “Amazon Compute SLA Credit Request – Region-Level Claim” in the subject line;
  2. the dates, times, and affected AWS region of each Unavailability incident that you are claiming;
  3. the resource IDs for the affected Included Service; and
  4. your request logs that document the errors and corroborate your claimed outage**.

Instance-Level SLA requests must include:

  1. the words “Amazon Compute SLA Credit Request – Instance-Level Claim” in the subject line;
  2. the dates, times, and the affected AWS region and AZ of each Unavailability incident that you are claiming;
  3. the resource IDs for the affected Single EC2 Instances; and
  4. your request logs and other data necessary for AWS to validate your claimed outage**. ** Please replace any confidential or sensitive information with asterisks.

If a claim under the Region-Level or Instance-Level SLA is confirmed by us as valid, we will issue you a Service Credit within one billing cycle following the month in which your request is confirmed by us.

Your failure to provide the requested and other information as required above will disqualify you from receiving a Service Credit. Unless otherwise provided in the Agreement, this SLA sets forth your sole and exclusive remedies, and AWS’ sole and exclusive obligations, for any unavailability, non-performance, or other failure by us to provide the Included Services.

Amazon Compute Service Level Agreement - Credit Request and Payment Procedures

SLAが適用されないケース

SLAが適用されないケースは、以下のように定義されています。当然ですが、「利用者起因でEC2インスタンスに接続できなくなった」なんて場合は適用されません。

Amazon Compute SLA Exclusions

The Region-Level SLA and Instance-Level SLA, respectively, do not apply to any unavailability, suspension or termination of an Included Service, or any other Included Service performance issues, directly or indirectly:

  • (i) caused by factors outside of our reasonable control, including any force majeure event or Internet access or related problems beyond the demarcation point of the applicable Included Service;
  • (ii) that result from any actions or inactions of you or any third party, including failure to acknowledge a recovery volume or respond to resource health concerns;
  • (iii) that result from your equipment, software or other technology and/or third party equipment, software or other technology (other than third party equipment within our direct control);
  • (iv) arising from our suspension or termination of your right to use the applicable Included Service in accordance with the Agreement (collectively, the “Amazon Compute SLA Exclusions”).

If availability is impacted by factors other than those used in our Monthly Uptime Percentage calculation, then we may issue a Service Credit considering such factors at our discretion.

Amazon Compute Service Level Agreement - Amazon Compute SLA Exclusions

SLAを過信しないで

SLAのAはAssurance (保証)ではなく、Agreement (合意)です。

そのため、「SLA 99.5% = 99.5% 以上必ず停止しない」という保証ではないので要注意です。

SLAを満たさない場合は利用費に応じたサービスクレジットが返還されるというものであり、障害発生による経済的損失をAWSに請求できるものではありません。

障害発生時のビジネスインパクトが大きい場合はMulti-AZ構成にするなど、利用者側で可用性を高める対応が必要です。

このブログが誰かの助けになれば幸いです。

以上、東京オフィスの のんピ(@non____97)でした!