Application service is one term for three different things, and the confusion is the whole problem. Most often, and in the sense closest to networking, application services are the support functions that keep an application fast, secure and available: traffic management, web application firewalls, load balancing, DDoS protection and API management.
Second, an application service provider, or ASP, is a business that delivers software over the internet, the model that led to software as a service. Third, in enterprise architecture, an application service is an abstract unit of functional behavior. The senses are unrelated, and the first question is always which one is meant.
- Application services (plural) are the support functions around an app: load balancing, WAF, DDoS protection, API management
- An application service provider (ASP) delivers software over the internet, the precursor to SaaS
- In enterprise architecture, an application service is an abstract unit of functionality
- The three senses are unrelated; the first is the one networking usually means
- The disambiguating question is always which meaning is intended
On this page
Delivery servicesSense 1: the services that deliver and secure an application
This is the meaning a network or infrastructure person almost always intends, and it is the one this site's other pages connect to.
They sit around the application, not inside it. F5's definition is exact: application services are the technologies, such as traffic management, web application firewalls, load balancing, DDoS protection and API management, that interact with the environment around the application, enabling it to adapt to changing conditions. The application does its work; the application services keep it reachable and safe.
They exist for performance, security and availability. In F5's words, application services help organizations boost performance, maintain availability, improve network and application security, and gain visibility into the behavior and health of their apps. Each of those is a job the application itself does not do for itself.
They work by shaping and steering traffic. These services ensure the performance, security and operability of the applications they support by shaping and steering traffic in response to the application's state and the nature of the traffic. That is why they live in the network path rather than in the code.
You already know the individual ones. A load balancer spreading requests across servers is an application service. A web application firewall filtering malicious requests is one. DDoS protection and API management are two more. Application services is the umbrella term for the whole set of these functions.
Where they run. Historically these services ran on a dedicated appliance, an application delivery controller, sitting in front of the servers.
Today the same functions are just as often delivered as cloud services or software instances, so an organization managing hundreds or thousands of applications can apply consistent performance and security controls across environments without a box per site. The form factor changed; the job of the application services did not.
The ASPSense 2: the application service provider (ASP)
This is a delivery model, and it is where the term meets its own history.
An ASP hosts software you reach over the internet. An application service provider delivers software from a centralized, secure server to multiple clients over the internet; customers access the application through a web browser or client portal, with no local installation. Wikipedia's definition matches: an ASP is a business providing application software generally through the web.
The provider runs everything. The ASP handles application management, including updates, maintenance and security, and protects client data with encryption, firewalls and backups. The customer uses the software; the provider operates it.
It is the ancestor of SaaS. ASPs paved the way by hosting traditional software for remote access; software as a service is the modern, cloud-native version of the same idea.
An ASP often hosted one copy of conventional software per customer, while SaaS is built multi-tenant from the start, but the customer experience, software you use over the internet without installing, is the shared thread.
Why the term persists. The ASP label is older and less used now than SaaS, but it still appears in contracts, in older documentation, and in the acronym, which is why a search for application service lands on it. When someone means the delivery model, they usually now say SaaS.
Why it matters to a buyer. The ASP or SaaS model moves the cost of running the software, the servers, the updates, the security patching, onto the provider, in exchange for a subscription and a dependency.
The trade is the same one behind any hosted service: less to operate in-house, against vendor lock-in and reliance on the provider staying available. It is the delivery side of the CapEx-versus-OpEx decision.
Architecture senseSense 3: the enterprise architecture meaning
The third sense is precise, narrow and easy to miss if you have never worked in enterprise architecture.
It is an abstraction, on purpose. In enterprise architecture, an application service is a well-defined component of functional behavior that abstracts what application functionality is provided, without specifying how it is implemented. It describes a capability, not a product.
It exists to model before building. This abstraction lets architects model the intended structure and responsibilities of the application layer before selecting or building the actual applications. The application service is the placeholder for a capability the business needs, which a real application will later provide.
It is a modeling term, not a running thing. Unlike the first two senses, this one does not name software you buy or traffic you steer.
It names a box on an architecture diagram, in frameworks such as ArchiMate, that says what is needed without committing to how. Confusing it with the delivery sense is a common cross-wire between architects and engineers.
Telling them apartTelling them apart quickly
Because the term is genuinely ambiguous, a few cues resolve it fast.
Plural and infrastructure words mean sense 1. If the sentence lists load balancing, WAF or API management, or talks about performance and availability, it is the application delivery sense.
"Provider" or "ASP" means sense 2. If the word provider is attached, or the topic is who hosts and delivers the software, it is the delivery model, and the modern word for it is usually SaaS.
Architecture, capability or modeling context means sense 3. If the setting is an architecture diagram, a capability map, or a framework like ArchiMate, it is the abstract functional unit.
When in doubt, ask which. The senses are unrelated enough that guessing wrong sends the whole conversation in the wrong direction. One clarifying question saves the misunderstanding.
PitfallsWhere people go wrong
Assuming SaaS when someone means delivery services. An engineer who hears application services and thinks hosted software misses that the speaker meant load balancing and WAF. In a networking context, sense 1 is the default.
Assuming delivery services when someone means the ASP model. The reverse also happens: a procurement or contract discussion that says application service usually means the provider and the hosting model, not traffic management.
Treating the architecture sense as a product. An application service on an architecture diagram is a capability to be filled, not software to be bought. Asking the vendor for their application service, meaning the ArchiMate box, produces confusion on both sides.
Reading a search result in the wrong sense. A search for application service returns all three meanings mixed together. Check which one a given page is using before taking its definition as the answer.
Letting the acronym hide the meaning. ASP is also an old Microsoft web technology, Active Server Pages, unrelated to application service provider. The acronym alone does not disambiguate; the surrounding words do.
ComparisonThree things called an application service
| Criterion | Application services | Application service provider | EA application service |
|---|---|---|---|
| What it is | Functions that deliver and secure an app | A business hosting software | An abstract unit of functionality |
| Concrete or abstract | Concrete technology | A concrete service | Abstract, a model element |
| Examples | Load balancing, WAF, API management | A hosted billing or CRM system | A box on an architecture diagram |
| Modern equivalent | Application delivery, ADC | Software as a service | ArchiMate application service |
| Closest audience | Network and infrastructure | Procurement, IT services | Enterprise architects |
| The giveaway word | performance, availability, traffic | provider, hosted, delivered | capability, model, framework |
The giveaway-word row is the fastest way to tell which sense a page or a person means.
FAQFrequently asked questions
What is an application service?
It depends on context. In networking it usually means the support functions that keep an application fast, secure and available, such as load balancing, web application firewalls and API management. It can also mean an application service provider that hosts software over the internet, or, in enterprise architecture, an abstract unit of application functionality.
What are application services in networking?
The technologies around an application that manage its traffic and protect it: traffic management, web application firewalls, load balancing, DDoS protection and API management. They ensure performance, security, availability and visibility for the applications they support.
What is an application service provider?
A business that delivers software from a central, secure server to many customers over the internet, with access through a browser or portal and no local installation. The provider handles updates, maintenance and security.
What is the difference between an ASP and SaaS?
An ASP hosts software, often a conventional application per customer, for remote access; SaaS is the cloud-native, multi-tenant evolution of the same idea. ASPs paved the way and the term is largely superseded by SaaS.
What does application service mean in enterprise architecture?
A well-defined component of functional behavior that describes what an application provides without specifying how it is built. It lets architects model the application layer before choosing or building the actual applications.
Are application services the same as microservices?
No. Microservices are an architecture for building one application out of small independent parts. Application services, in sense one, are the delivery and security functions around an application, whatever its internal architecture.
Is a load balancer an application service?
Yes, in the first sense. Load balancing is one of the core application services, alongside web application firewalls, DDoS protection and API management.
Why does one term have three meanings?
The three grew up in different fields, networking, IT service delivery, and enterprise architecture, and each kept the phrase. They are not related, which is why context, not the words themselves, tells you which is meant.
Which meaning should I assume?
In a networking or infrastructure setting, the delivery-and-security sense. In a procurement or hosting discussion, the provider sense, though people now usually say SaaS. In an architecture setting, the abstract unit. When the setting is unclear, ask.
Is ASP the same as Active Server Pages?
No. ASP as application service provider is a hosting model; ASP as Active Server Pages is an old Microsoft web technology. The acronym collides; the surrounding words tell them apart.
Are application services part of an ADC?
Yes. An application delivery controller is a device or platform that provides many of the sense-one application services, load balancing, traffic management, and often a web application firewall, in one place.
Do I need application services for a small setup?
The functions still apply at any size, but they are often bundled: a small site may get load balancing and a WAF from a single cloud service rather than separate appliances. The need scales with how much the application matters, not with headcount.
What is the difference between application services vs SaaS?
SaaS is finished software you rent and use through a browser, with the vendor running everything. Application services are work done on software you own or control: development, integration, hosting, maintenance and support. A company can buy both, for example a SaaS product plus application services to connect it to older systems.
Keep readingRelated concepts
Read next · Infrastructure What a Load Balancer Does, and the Two Decisions Behind It One of the core sense-one application services, explained on its own. Open this next12 min- Managed IT · 10 min CapEx and OpEx in IT, and Why the Budget Line Shapes the Build The buy-versus-subscribe decision behind the ASP and SaaS model.
- Infrastructure · 11 min Quality of Service, and the Condition It Needs to Do Anything How the network decides which application traffic goes first under load.