# Concepts

Easegress operates on the foundational concepts of controllers, pipelines, and filters.

### Controllers

The Easegress controller is the central unit responsible for various operations. Different controllers perform specific tasks; for example, the `HTTPServer` controller handles HTTP traffic. These controllers can be created, updated, edited, or deleted using `egctl` commands along with YAML files.

Controllers like `ConsulServiceRegistry`, `EtcdServiceRegistry`, `EurekaServiceRegistry`, `ZookeeperServiceRegistry`, and `NacosServiceRegistry` are specialized for service registry tasks.

Others, such as `HTTPServer` and `GRPCServer`, focus on managing network traffic.

Still others, like `AutoCertManager` and `GlobalFilter`, are designed to handle specific business logic.

For more information, refer to [controllers](../07.Reference/7.01.Controllers.md).

### Pipelines

The `Pipeline` is a built-in Easegress mechanism designed to orchestrate a sequence of filters for handling requests. It often operates in conjunction with `HTTPServer` and serves as its backend. The pipeline comprises a flow of filters executed in a defined sequence.

A sample configuration might look like:

```yaml
name: pipeline-demo
kind: Pipeline
flow:
- filter: validator
- filter: proxy
...

filters:
- name: validator
  kind: Validator
  ...
- name: proxy
  kind: Proxy
  ...
...
```

For more information, refer to [pipeline explained](../02.Tutorials/2.3.Pipeline-Explained.md).


### Filters

A Filter acts as a processor for handling requests and responses. In a pipeline, multiple filters are orchestrated to process the input sequentially, each returning a string result upon completion. Filters are primarily utilized within `Pipelines`.



For instance, the `Proxy` filter serves as a gateway to backend services, while the `RateLimiter` filter enhances service reliability and availability by regulating the rate of incoming requests within a specified time frame.

For more information, refer to [filters](../07.Reference/7.02.Filters.md).