Why Amazon’s Cloud Computing Outage Didn’t Violate Its SLA

Amazon’s cloud computing outage on April 21 and April 22 can be interpreted in one of two ways: (1) either the outage constitutes a reflection on Amazon’s EC2 platform and its processes for disaster recovery situations; or (2) the outage represents a commentary on the state of the cloud computing industry as a whole. The outage began on Thursday and involved problems specific to Amazon’s Northern Virginia data center. Companies affected by the outage include HootSuite, FourSquare, Reddit, Quora and other start-ups such as BigDoor, Mass Relevance and Spanning Cloud Apps. Hootsuite—a dashboard that allows users to manage content on a number of websites such as Facebook, LinkedIn, Twitter and WordPress—experienced a temporary crash on Thursday that affected a large number of sites. The social news website Reddit was unavailable until noon on Thursday, April 21. BigDoor, a 20 person start-up that provides online game and rewards applications, had restored most of its services by Friday evening even though its corporate website remained down. Netflix and Recovery.gov, meanwhile, escaped the Amazon outage either unscathed or with minimal interruption.

Amazon’s EC2 platform currently has five regions: US East (Northern Virginia), US West (Northern California), EU (Ireland), Asia Pacific (Singapore), and Asia Pacific (Tokyo). Each region is composed of multiple “Availability Zones”. Customers who launch server instances in different Availability Zones can, according to Amazon Web Services’s website, “protect [their] applications from failure of a single location.” The Amazon outage underscores how EC2 customers can no longer depend on having multiple “Availability Zones” within a specific region as insurance against system downtime. Customers will need to ensure their architecture plans for duplicate copies of server instances in multiple regions.

Amazon’s SLAs commit to 99.5% system uptime for customers who have deployments in more than one availability zone within a specific region. However, the SLA guarantees only the ability to commit to connect to and provision instances. On Thursday and Friday, Amazon’s US-East customers could still connect to and provision instances, but the outage adversely affected their deployments because of problems with Amazon’s Elastic Block Storage (EBS) and Relational Database Service (RDS) platforms. EBS is a storage database and RDS provides a way of relating multiple databases that store data provisioned on an EC2 platform. Because Amazon’s problems were confined to EBS and RDS in the US East region, Amazon’s SLA for customers affected by the outage was not violated. The immediate consequence here is that Amazon EC2 customers will need to deploy copies of the same server instance in multiple regions to guarantee 100% system uptime, assuming, of course, that the wildly unlikely scenario that multiple Amazon cloud computing regions experience outages at the same time never transpires.

Anyone familiar with the cloud computing industry knows full well that Amazon, Rackspace, Microsoft and Google have all experienced glitches resulting in system downtime in the last three years. The multiple instances of system downtime across vendors points to the immaturity of the technological architecture and processes for delivering cloud computing services. Until the architecture and processes for cloud computing operational management improves, customers will need to seriously consider the costs of redundant data architectures that insure them against system downtime in comparison with the risk and costs of actual downtime.

For a non-technical summary of the technical issues specific to the outage, see Cloud Computing Today’s “Understanding Amazon Web Services’s 2011 Outage“.

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Categories: Amazon Web Services, Cloud Computing, IaaS | Tags: , , , , , , , , , , , , | 6 Comments

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6 thoughts on “Why Amazon’s Cloud Computing Outage Didn’t Violate Its SLA

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