---
title: Services
summary: null
url: https://www.fastly.com/documentation/reference/api/services
---

A service is the Fastly term for a set of configuration to apply to an identifiable portion of inbound traffic. Traffic is routed to a service based on the domains which are assigned to it, and the service may forward that traffic to any of its assigned backends.

A selection of APIs exists to create services and define their inputs and outputs. To configure the behavior of services, see the [VCL objects](https://www.fastly.com/documentation/reference/api/vcl-services/) section.

- [Backend](https://www.fastly.com/documentation/reference/api/services/backend/) - A backend (also sometimes called an origin server) is a server identified by IP address or hostname, from which Fastly will fetch your content. There can be multiple backends attached to a service, but each backend is specific to one service. By default, if only one backend is defined in a service configuration, it will be used for all requests provided it meets the <a href="https://www.fastly.com/documentation/reference/api/vcl-services/condition">conditions</a> attached to it, if any. If multiple backends are defined, the backend that is used for a request is the one with the highest-priority condition attached to it, out of all conditions that this request satisfies. If multiple conditions match the request with the same (highest) priority, one is chosen arbitrarily. If there are no backends with conditions that match the request, then the backend without any conditions is chosen. If there are multiple such backends, one is chosen arbitrarily. The behavior described above can be modified by using the <code>auto_loadbalance</code> field described below. These endpoints can be used with static backends only, not <a href="https://www.fastly.com/documentation/guides/integrations/backends/#dynamic-backends">dynamic backends</a>.
- [Domain](https://www.fastly.com/documentation/reference/api/services/domain/) - A domain represents the domain name through which visitors will retrieve content. There can be multiple domains for a service.
- [Edge data storage](https://www.fastly.com/documentation/reference/api/services/resources/)
- [Health check](https://www.fastly.com/documentation/reference/api/services/healthcheck/) - Health checks are used to customize the way Fastly checks on your Backends. If an origin server is marked unhealthy due to health checks, Fastly will stop attempting to send requests to it. If all origin servers are marked unhealthy, Fastly will attempt to serve stale. If no stale object is available, a 503 will be returned to the client.
- [Image Optimizer Default Settings](https://www.fastly.com/documentation/reference/api/services/image-optimizer-default-settings/) - Configures default settings for Fastly Image Optimizer requests, configuring the way images are optimized when not overridden by URL parameters on specific requests.
- [Package](https://www.fastly.com/documentation/reference/api/services/package/) - Fastly Compute is a computation platform capable of running custom binary packages that you compile on your own systems and upload to Fastly. These packages are associated with a service version and are deployed to Fastly's edge network.
- [Resource links](https://www.fastly.com/documentation/reference/api/services/resource/) - A resource link represents a link between a shared resource (such as an kv store or config store) and a service version.
- [Service](https://www.fastly.com/documentation/reference/api/services/service/) - A Service represents the configuration for a website, app, API, or anything else to be served through Fastly. A Service can have many Versions, through which Backends, Domains, and more can be configured.
- [Version](https://www.fastly.com/documentation/reference/api/services/version/) - A Version represents a specific instance of the configuration for a service. A Version can be cloned, locked, activated, or deactivated.