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Peihao Yang edited this page Mar 2, 2022 · 2 revisions

Sentinel takes "flow" as breakthrough point, and works on multiple fields including flow control, traffic shaping, circuit breaking and system adaptive protection, to guarantee reliability and resilience for microservices.

Sentinel adopts Chain-of-Responsibility pattern. The user-defined rules will be automatically checked via slots in base::SlotChain. Generally, there are several steps when using Sentienl:

  1. Add dependancy and initialize configurations on Sentinel.
  2. Define a resource to be protected and build Sentinel entry.
  3. Load the rules defined for each resource.
  4. Write the codes at entry and exit points.

Thorough examples have been provided in our repository.

Add Dependency

Add the dependency in Cargo.toml:

[dependencies]
sentinel-core = { version = "0.1.0", features = ["full"] }

Optional features lists:

  • macro：Support procedural macro, simplify the resource and rule definitions, refer to example.
  • async：Support asynchronous resources, refer to example.
  • exporter：Export metric statistics to Prometheus, refer to example and Sentinel Prometheus Metrics Definitions.
  • logger_env: Use env_logger to initialize logging.
  • logger_log4rs: Use log4rs to initialize logging.
  • ds_consul: Use Consul to configure rules dynamically.
  • ds_etcdv3：Use etcd to configure rules dynamically.
  • ds_k8s：Use k8s to configure rules dynamically.
  • metric_log: Store formatted logs on Sentinel resources.

General Configurations and Initialization

Sentinel needs to be initialized. The api module provides following interfaces:

  • init_default(): Load configurations from environment variable. For undefined configurations, use default values.
  • init_with_config_file(config_path: &mut String): Load configurations from a YAML file, refer to example。。
  • init_with_config(config_entity: ConfigEntity): Use hand-crafted ConfigEntity to initialize Sentinel，refer to example。。

Example:

use sentinel_rs::{init_default, logging};
init_default().unwrap_or_else(|err| logging::error!("{:?}", err));

Resouce Definition

A snippet of codes is regarded as resources in Sentinel, which can be protected by defining their entries.

By constructing EntryBuilder and calling the build() method, we create Entry.

Example：

If the calling is blocked, build() will return an error.

use sentinel_core::base;
use sentinel_core::api::EntryBuilder;
let entry_builder = EntryBuilder::new(res_name.clone())
	.with_traffic_type(base::TrafficType::Inbound);
if let Ok(entry) = entry_builder.build() {
	// The request is allowed to be processed.
	// after finish the logic, exit the entry.
    entry.borrow().exit()
} else {
	// The request is blocked.
	// you do not need to call `exit()` on entry now.
}

Load Sentinel Rules

Manually Create Sentinel Entry and Load Rules

Sentinel supports loading hand-crafted rules. The method load_rules() will overload all of the rules defined before. The method append_rules() will append rules incrementally. Currently, this is the only way to define several rules for a single resource. For example:

flow::load_rules(vec![Arc::new(flow::Rule {
    resource: "example".into(),
    threshold: 10.0,
    calculate_strategy: flow::CalculateStrategy::Direct,
    control_strategy: flow::ControlStrategy::Reject,
    ..Default::default()
})]);

Via Attribute-Like Macros

We also provide macros to help you define Sentinel resources and load rules easily:

#[flow(threshold=10.0, calculate_strategy=Direct)]
pub fn task() -> u32 {}

When using macro, the resource name will be automatically generated as the method name. Since there is not function overloading in Rust, the resource name will be unique. Sentinel will check if the rule with the same resource name has been loaded.

In the example above, the macro modify the function signature of task, returning Result<u32, String> in the new one. Then, it appends rules to the rule manager, call EntryBuilder to create Sentinel entry, check if the entry pass the rule checking. If the tasks is carried successfully, it will return an Ok(u32). Otherwise, Err(String) will be returned.

The shortcoming is that there is no way to define several rules on a single resource with this macro.

Via Dynamic Datasource

Sentinel supports use dynamically load Sentinel rules, refer to

More Resources

See the Wiki for
full documentation, examples, blog posts, operational details and other information.

See the Sentinel for the document website.

See the 中文文档 for document in Chinese.

Clone this wiki locally