- The CircuitBreaker only analyses what happens after it is positioned in the middleware chain. What happens before has no impact on its state.
- The CircuitBreaker only affects the routers that use it. Routers that don't use the CircuitBreaker won't be affected by its state.
Each router will eventually gets its own instance of a given circuit breaker.
If two different routers refer to the same circuit breaker definition, they will get one instance each. It means that one circuit breaker can be open while the other stays closed: their state is not shared.
This is the expected behavior, we want you to be able to define what makes a service healthy without having to declare a circuit breaker for each route.
# Latency Check labels: - "traefik.http.middlewares.latency-check.circuitbreaker.expression=LatencyAtQuantileMS(50.0) > 100"
# Latency Check apiVersion: traefik.containo.us/v1alpha1 kind: Middleware metadata: name: latency-check spec: circuitBreaker: expression: LatencyAtQuantileMS(50.0) > 100
# Latency Check [http.middlewares] [http.middlewares.latency-check.circuitBreaker] expression = "LatencyAtQuantileMS(50.0) > 100"
# Latency Check http: middlewares: latency-check: circuitBreaker: expression: "LatencyAtQuantileMS(50.0) > 100"
There are three possible states for your circuit breaker:
- Close (your service operates normally)
- Open (the fallback mechanism takes over your service)
- Recovering (the circuit breaker tries to resume normal operations by progressively sending requests to your service)
While close, the circuit breaker only collects metrics to analyze the behavior of the requests.
At specified intervals (
checkPeriod), it will evaluate
expression to decide if its state must change.
While open, the fallback mechanism takes over the normal service calls for a duration of
After this duration, it will enter the recovering state.
While recovering, the circuit breaker will progressively send requests to your service again (in a linear way, for
If your service fails during recovery, the circuit breaker becomes open again.
If the service operates normally during the whole recovering duration, then the circuit breaker returns to close.
Configuring the Trigger¶
You can specify an
expression that, once matched, will trigger the circuit breaker (and apply the fallback mechanism instead of calling your services).
expression can check three different metrics:
- The network error ratio (
- The status code ratio (
- The latency at quantile, in milliseconds (
If you want the circuit breaker to trigger at a 30% ratio of network errors, the expression will be
NetworkErrorRatio() > 0.30
You can trigger the circuit breaker based on the ratio of a given range of status codes.
ResponseCodeRatio accepts four parameters,
The operation that will be computed is sum(
from) / sum (
If sum (
dividedByTo) equals 0, then
ResponseCodeRatio returns 0.
to is exclusive.
For example, the expression
ResponseCodeRatio(500, 600, 0, 600) > 0.25 will trigger the circuit breaker if 25% of the requests returned a 5XX status (amongst the request that returned a status code from 0 to 5XX).
You can trigger the circuit breaker when a given proportion of your requests become too slow.
For example, the expression
LatencyAtQuantileMS(50.0) > 100 will trigger the circuit breaker when the median latency (quantile 50) reaches 100MS.
You must provide a float number (with the trailing .0) for the quantile value
Using multiple metrics¶
You can combine multiple metrics using operators in your expression.
Supported operators are:
- AND (
- OR (
ResponseCodeRatio(500, 600, 0, 600) > 0.30 || NetworkErrorRatio() > 0.10 triggers the circuit breaker when 30% of the requests return a 5XX status code, or when the ratio of network errors reaches 10%.
Here is the list of supported operators:
- Greater than (
- Greater or equal than (
- Lesser than (
- Lesser or equal than (
- Equal (
- Not Equal (
The fallback mechanism returns a
HTTP 503 Service Unavailable to the client (instead of calling the target service).
This behavior cannot be configured.
The interval used to evaluate
expression and decide if the state of the circuit breaker must change.
CheckPeriod is 100ms. This value cannot be configured.
FallbackDuration is 10 seconds. This value cannot be configured.
The duration of the recovering mode (recovering state).
RecoveringDuration is 10 seconds. This value cannot be configured.