Availability

These concerns center on critical applications and data being available. Well-publicized incidents of cloud outages include Gmail (one-day outage in mid-October 2008), Amazon S3 (over seven-hour downtime on July 20, 2008), and FlexiScale (18-hour outage on October 31, 2008).

Availability Threat #1. Uptime

  As with the Traditional Security concerns, cloud providers argue that their server uptime compares well with the availability of the cloud user’s own data centers.

Uptime

Besides just services and applications being down, this includes the concern that a third-party cloud would not scale well enough to handle certain applications. SAP’s CEO, Leo Apotheker said: “There are certain things that you cannot run in the cloud because the cloud would collapse…Don't believe that any utility company is going to run its billing for 50 million consumers in the cloud.”

Availability Threat #2. Single point of failure.

Single Point of Failure

Cloud services are thought of as providing more availability, but perhaps not – there are more single points of failure and attack.

Availability Threat #3. Assurance of computational integrity.

Assurance of Computaional Integrity

Can an enterprise be assured that a cloud provider is faithfully running a hosted application and giving valid results? For example, Stanford's Folding@Home project gives the same task to multiple clients to reach a consensus on the correct result.