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Availability considerations for the IaaS delivery model should include both a computing
and storage (persistent and ephemeral) infrastructure in the cloud. IaaS
providers may also offer other services such as account management, a
message queue service, an identity and authentication service, a database
service, a billing service, and monitoring services. Hence, availability
management should take into consideration all the services that you depend
on for your IT and business needs. Customers are responsible for all
aspects of availability management since they are responsible for
provisioning and managing the life cycle of virtual servers. Managing your IaaS virtual infrastructure in the cloud depends on
five factors: Availability of a CSP network, host, storage, and support
application infrastructure. This factor depends on the
following: CSP data center architecture, including a geographically
diverse and fault-tolerance architecture. Reliability, diversity, and redundancy of Internet
connectivity used by the customer and the CSP. Reliability and redundancy architecture of the hardware and
software components used for delivering compute and storage
services. Availability management process and procedures, including
business continuity processes established by the CSP. Web console or API service availability. The web console and
API are required to manage the life cycle of the virtual servers.
When those services become unavailable, customers are unable to
provision, start, stop, and deprovision virtual servers. SLA. Because this factor varies across CSPs, the SLA should be reviewed and reconciled, including
exclusion clauses.
Availability of your virtual servers and the attached storage (persistent and
ephemeral) for compute services (e.g., Amazon Web Services’ S3 and Amazon Elastic Block Store). Availability of virtual storage that your users and virtual
server depend on for storage service. This includes both synchronous
and asynchronous storage access use cases. Synchronous storage access
use cases demand low data access latency and continuous availability,
whereas asynchronous use cases are more tolerant to latency and
availability. Examples for synchronous storage use cases include
database transactions, video streaming, and user authentication.
Inconsistency or disruptions to storage in synchronous storage has a
higher impact on overall server and application availability. A common
example of an asynchronous use case is a cloud-based storage service
for backing up your computer over the Internet. Availability of your network connectivity to the Internet or
virtual network connectivity to IaaS services. In some cases, this can
involve virtual private network (VPN) connectivity between your
internal private data center and the public IaaS cloud (e.g., hybrid
clouds). Availability of network services, including a DNS, routing
services, and authentication services required to connect to the IaaS
service.
IaaS Health MonitoringThe following options are available to IaaS customers for managing the health of their
service: Service health dashboard published by the CSP. CCID (this database is generally community-supported, and
may not reflect all CSPs and all incidents that have
occurred). CSP customer mailing list that notifies customers of occurring
and recently occurred outages. Internal or third-party-based service monitoring tools (e.g.,
Nagios) that periodically check the health of your
IaaS virtual server. For example, Amazon Web Services (AWS) is offering a cloud
monitoring service called CloudWatch. This web service provides monitoring for
AWS cloud resources, including Amazon’s Elastic Compute Cloud (EC2). It also provides
customers with visibility into resource utilization, operational
performance, and overall demand patterns, including metrics such as
CPU utilization, disk reads and writes, and network traffic. Web console or API that publishes the current health status of
your virtual servers and network.
Similar to SaaS service monitoring, customers who are hosting
applications on an IaaS platform should take additional steps to monitor
the health of the hosted application. For example, if you are hosting an
e-commerce application on your Amazon EC2 virtual cloud, you should
monitor the health of both the e-commerce application and the virtual
server instances.
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