Service Level Agreements

Companies spend so much money creating legal agreements. Very few people read them.

I am not a lawyer. I have been around long enough to have worked with lots of lawyers on lots of legal documents. Almost always, the boring and tedious side of IT. This is not to say that legal matters are not important - they are very important.

I do not believe much in SLAs. You need to implement fault tolerance and recovery mechanisms that function independently from cloud SLAs. There are so many individual items that can fail that are not under the cloud vendors control. Design your systems for failure. If a cloud vendor has a poor real-world SLA, they will go broke. They need to keep the real-world numbers up just to survive.

Reference Documents:

  • Alibaba Cloud International Website Elastic Compute Service (ECS) Service Level Agreement - February 6, 2017
  • Amazon Compute Service Level Agreement - February 12, 2018

  • Let's review what is offered by both vendors

    Both documents are very similar. Both have similar types of exclusions. Both are limited to crediting you 30%. Remember, this is a service credit and not a refund. Also note that this limit is 30%. If the downtime is longer than 30% of a month .... Of course, you have monitoring, alerting and logging enabled AND you take the time to manage these services.


    The key difference between SLAs is in the monthly uptime percentage. For AWS this is 99.99%. For Alibaba this is 99.95%.

    Given that the average month has 30 days, or 43,200 minutes:

  • AWS provides a downtime of 4.3 minutes or less per month.
  • Alibaba provides a downtime of 21.6 minutes or less per month.
  • Neither of these numbers include "Scheduled Downtime". You need to pay attention to cloud vendor notices that include scheduled downtime and plan accordingly.

    Neither of these numbers are good enough today. This is why load balancing, health checks, auto scaling and failover are critical in today's eCommerce world. Just getting to AWS's 4-nines is expensive and should be commended. I expect that Alibaba will also get to 4-nines as their infrastructure practices mature.

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