Circuit Breaker Policy

Policy name

Circuit Breaker

Summary

Prevents an upstream from receiving too many requests or connections

Category

Quality of Service

First Flex Gateway version available

v1.9.0

Returned Status Codes

503 - Service Unavailable

Summary

The Circuit Breaker policy prevents upstream services from receiving too many requests or connections at a time. If the defined maximums are reached, Flex Gateway returns a 503 - Service Unavailable error.

For Managed Flex Gateways or Connected Mode, each API instance has its own independent limit when requesting the same upstream, allowing each to use the full maximum. In Local Mode, the limits are shared among different API instances, so they must all adhere to the same upstream maximum. For all modes, maximums are not distributed across replicas; each Gateway can use the full maximum.

The Circuit Breaker policy is an extension of the Envoy upstream clusters circuit breaking feature. To learn more about the Envoy’s circuit breaking, see Circuit Breaking Leaving the Site in the Envoy documentation.

Configuring Policy Parameters

Flex Gateway Local Mode

In Local Mode, you apply the Circuit Breaker policy to your API via declarative configuration files. Refer to the following policy definition and table of parameters:

apiVersion: gateway.mulesoft.com/v1alpha1
kind: PolicyBinding
metadata:
  name: upstream-policy
spec:
  targetRef:
    Kind: Service
    name: upstream
  policyRef:
    name: circuit-breaker-flex
  config:
    thresholds:
      maxConnections: <number> // OPTIONAL
      maxPendingRequests: <number> // OPTIONAL
      maxRequests: <number> // OPTIONAL
      maxRetries: <number> // OPTIONAL
      maxConnectionPools: <number> // OPTIONAL

For Local Mode, the limits are not independent, so different API instances share the maximums for an upstream.

Parameter Required or Optional Description

Parameter	Required or Optional	Description
`maximumConnections`	Optional	Maximum number of connections per API to an upstream.
`maximumPendingRequests`	Optional	Maximum number of queued requests while waiting for a connection.
`maximumRequests`	Optional	Maximum number of outstanding requests to an upstream.
`maximumRetries`	Optional	Maximum number of outstanding retries.
`maximumConnectionPools`	Optional	Maximum number of connection pools concurrently initiated to an upstream.

maximumConnections

Optional

Maximum number of connections per API to an upstream.

maximumPendingRequests

Optional

Maximum number of queued requests while waiting for a connection.

maximumRequests

Optional

Maximum number of outstanding requests to an upstream.

maximumRetries

Optional

Maximum number of outstanding retries.

maximumConnectionPools

Optional

Maximum number of connection pools concurrently initiated to an upstream.

Resource Configuration Example

This example defines a policy of three requests every six seconds:

apiVersion: gateway.mulesoft.com/v1beta1
kind: Configuration
metadata:
  name: circuit-breaker
  namespace: test-ns
spec:
  circuitBreaker:
    thresholds:
      maxConnections: 1
      maxPendingRequests: 1
      maxRequests: 1
      maxRetries: 1
      maxConnectionPools: 1

Flex Gateway Connected Mode

When you apply the Rate Limiting policy to your API from the UI, you can configure the following parameters:

Parameter	Required or Optional	Description
Maximum connections	Optional	Maximum number of connections per API to an upstream.
Maximum pending requests	Optional	Maximum number of queued requests while waiting for a connection.
Maximum requests	Optional	Maximum number of outstanding requests to an upstream.
Maximum retries	Optional	Maximum number of outstanding retries.
Maximum connection pools	Optional	Maximum number of connection pools concurrently initiated to an upstream.

Parameter

Required or Optional

Description

Maximum connections

Optional

Maximum number of connections per API to an upstream.

Maximum pending requests

Optional

Maximum number of queued requests while waiting for a connection.

Maximum requests

Optional

Maximum number of outstanding requests to an upstream.

Maximum retries

Optional

Maximum number of outstanding retries.

Maximum connection pools

Optional

Maximum number of connection pools concurrently initiated to an upstream.

For Managed Flex Gateways or Connected Mode, each API instance has its own independent limit when requesting the same upstream, allowing each to use the full maximum.