A web application server runs dynamic application work; an SLA states agreed service targets. IaaS describes what a cloud provider supplies, while RPO and RTO describe recovery objectives. Read each term by its layer and decision rather than as a generic promise that a site will stay up.
Core words
The diagram separates runtime, service model, and availability or recovery targets in an operations plan.
| English term | Meaning and use |
|---|---|
availability | The degree to which a service can perform its intended function when needed, commonly measured over a defined period. |
WAS(Web Application Server) | Web Application Server: software running dynamic application logic and often providing sessions, transactions, or database integration. |
SLA | Service Level Agreement: a provider-customer agreement defining service levels, scope, measurements, and responsibilities. |
PaaS | Platform as a Service: a managed platform for building, deploying, and running applications. |
SaaS | Software as a Service: provider-operated software accessed over a network. |
IaaS | Infrastructure as a Service: on-demand compute, storage, and networking resources exposed as a service. |
SAN | Storage Area Network: a dedicated network providing block-level storage connectivity to servers. |
Words to distinguish together
| English term | Meaning and use |
|---|---|
RPO | Recovery Point Objective: the targeted age of recoverable data after an incident, expressed as allowable data loss in time. |
RTO | Recovery Time Objective: the targeted maximum time to restore a service after an incident. |
NAS | Network-Attached Storage: storage exposing files over a network to clients. |
DAS | Direct-Attached Storage: storage connected directly to one host rather than accessed over a storage network. |
HA | High Availability: design and operation intended to keep a service running or restore it quickly after failures. |
ITSM | Information Technology Service Management: practices for planning, delivering, supporting, and improving IT services. |
ITIL | A framework of guidance and practices for IT service management; check the version used in a specific organization. |
Words encountered in code and operations
| English term | Meaning and use |
|---|---|
APM | Application Performance Monitoring or Management: observing application behavior and performance to find or prevent user impact. |
Load balancer | A component that distributes eligible traffic across backends under configured health and routing rules. |
Session | A logical period of interaction with state associated with a user or process. |
Classic ASP (Active Server Pages) | A legacy Microsoft IIS server-side scripting technology; distinct from ASP.NET and an application service provider. |
Jakarta Server Pages (JSP) | A Jakarta EE technology for generating dynamic server-side web content, formerly named JavaServer Pages. |
Reading these terms in context
RPO asks how far back recovered data may be; RTO asks how long restoration may take. High availability is a design goal and operational capability, not an automatic consequence of calling a service cloud-hosted. An SLA needs its own scope and measurement rules.
The SLA specifies the availability target; the recovery plan specifies RPO and RTO; the load balancer distributes eligible traffic.
Key takeaways
Sort the terms into runtime, service model, storage, and operations. PaaS supplies a managed platform, SaaS supplies operated software, and IaaS supplies infrastructure resources. NAS, SAN, and DAS describe different storage access patterns; they are not availability objectives.