🗓️ 12092024 1153
📎 #sentinel #resilience

SENTINEL DUMP

Degrade Rules Cheatsheet

RT-based Degradation

Triggered when average RT exceeds a threshold

• Grade: 0
• Works with slowRationThreshold to measure the percentage of slow calls that exceed the threshold

Parameter	Description
count	Threshold in miliseconds for response time
slowRationThreshold	Percentage of slow calls that exceed threshold
timeWindow	Degrade time (in seconds during which API is blocked)

Exception Ratio-based Degradation

Triggered when the error/exception ratio of requests exceeds a given threshold

GRADE: 1

Parameter	Description
count	Exception ratio threshold (0.2 => 20%)
timeWindow	Degrade time during which API is blocked
Use Case: Helps to degrade a service when a significant number of requests fail.

Exception Count-based Degradation

Triggered when the total number of exceptions in a time window exceeds a given threshold

GRADE: 2

Parameter	Description
count	Total number of exceptions that will trigger the degrade
timeWindow	Degrade time in which API is blocked
Use Case: Useful when you want to limit the total number of exceptions within a given time window.

Key Points to Remember:

• Degradation temporarily stops serving requests to a particular resource if certain thresholds are exceeded, allowing the system to recover.
• RT-based rules prevent a service from being overwhelmed by slow responses, whereas exception-based rules handle situations with high error rates.
• After the time window, the service will try to serve requests again. If the issue persists, it may degrade again.

Example

[
  {
    "resource": " POST:http://something",
    "count": 0.15,
    "timeWindow": 5,
    "grade": 1
  },
  {
    "resource": " POST:http://something",
    "count": 1200,
    "timeWindow": 5,
    "grade": 0,
    "slowRatioThreshold": 0.2
  }
]

• The first rule will degrade the service if the error ratio exceeds 15% over a 5-second period.
• The second rule will degrade the service if more than 20% of requests take longer than 1.2 seconds during a 5-second window.

---

References