Cloud Computing

These are notes form Cloud Computing and Architecture an O'Reilly book written by George Reese.

• The Cloud
• the cloud is more than just a term for the internet
• specifically it is a combination of software and infrastructure 
• accessible via a web browser
• zero capital expenditure to get started
• pay for uses not initialization
• Software
• Software as a Service (SaaS) term that refers to software in the cloud
• Available via a web browser
• On-Demand Availability
• Payment based on Usage
• Minimal IT demands
• web based deployment model
• does not care about host site
• does not care about operating system or language used to write program
• Example: Gmail
• provides same service as Apple Mail or Outlook but without the client
• Multitenancy
• server based software that supports the deployment of multiple clients in a single software instance
• used as advertisement but virtualization technologies renders benefits moot
• Hardware
• Hardware is requested, i.e. a server but not physically owned by user
• increase in security due to obscurity, 
• Difficulties of proprietary servers
• Capacity planning
• Upfront costs of SAN(storage area networks) or individual servers
• Hardware destruction
• Disaster and recovery i.e. entire servers go down
• Real Estate and Electricity Usage
• Difficulties subsumed into main distributor of cloud resources rather than individual companies creating proprietary networks
• Hardware Virtualization
• Servers can be partitioned into sections with its own memory, CPU, and disk footprints
• Has a significant performance penalty however is a non-issue because
• cloud vendors servers far superior in performance to capabilities of small business servers
• Cloud Storage
• replaces physical storage systems
• Operationally different from physical due to degraded performance but enhanced structure
• Impractical for runtime storage for an application such as for transaction applications
• Cloud Application Architectures
• Grid Computing
• breaks up processing into small chunks that can be processed in isolation
• i.e. SETI@home
• collected volumes of data processed and checked against other users, alternate example BOINC
• functional steps in grid computing
• both worker and manager watch message queue
• worker waits for new data set, pulls data set publish results
• manager reads results
• limited to financial, scientific, and large scale data problems
• Transactional Computing
• one or more pieces of incoming data processed together and establish relationships with data already in the system
• components form a cluster
• Nodes in a transactional system must be long lived rather than short lived in grid computing
• Mean time between failures (MTBF) number of physical nodes governs this so cloud has higher failure rate than proprietary servers, but this can be mitigated
• The Value of Cloud Computing
• IT infrastructure traditional vs cloud
• file server vs google docs, MS outlook vs gmail, server racks and firewall vs Amazon EC2
• Cloud reduces software licensing hassle, charged for use, software upgrades, hardware failure, # of technology assets, manage depreciation of it assets, capacity management
• IT infrastructures without special constraints are extremely expensive to start up compared to cloud services
• The Economics
• Capital Costs
• depreciation of servers and computers
• Cost Comparison
• cloud has no capital costs but has monthly service fees, setup costs, and staff costs
• However many large companies already have infrastructure in place, not necessarily cost effective for them to transition to cloud services
• Cloud Infrastructure Models
• Platform as a Service Vendor
• complete operational and deployment options
• Google App Engine
• Vendor Lock-in i.e. Python requirement for Google Apps
• Infrastructure as a Service
• Amazon Web Services

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