---
schema_version: "1"
id: d55a594a0f6af538e359f87af0cd49fa88db4832483d3d74df560d58788fa815
title: Circuit Breaker
collection: developer
version: current
locale: en-us
portal_url: https://docs.salesforce.com/developer/current/en-us/commerce-cloud/commerce-api/guides/custom-api-circuit-breaker.md
canonical_url: https://developer.salesforce.com/docs/commerce/pwa-kit-managed-runtime/guide/custom-api-circuit-breaker.html
source_site: developer.salesforce.com
content_type: documentation
content_hash: 436ca3d1ff39851f3c8e9befd59c77a62d774ed783eb73e6757a99b86ea1a58c
products:
  - Composable Storefront
  - Salesforce APIs
---
# Circuit Breaker

To ensure the stability of the platform by protecting it from excessive load, Custom APIs contain a **Circuit Breaker** mechanism. This functionality blocks API requests when a specific error threshold is exceeded.

## How it works

A circuit breaker is configured for every registered endpoint and each incoming request to that endpoint passes through it. How the circuit breaker acts depends on its internal state, which is defined by the recent script execution on the corresponding endpoint. The circuit breaker can be in one of three states: `closed`, `open`, or `half-open`.

The default state of a circuit breaker is `closed`, which means that the request is allowed to pass through to the implementation script.

If the execution of the implementation script results in an error, this error is tracked. Once the error rate exceeds the threshold of **50%**, this process is triggered:

1. The internal state changes to `open`. This change is logged.
2. For **60** seconds, any calls to the failing endpoint return an HTTP status code **503 - Service Unavailable** with the error type `custom-api-circuit-breaker-error`.
3. After **60** seconds, the internal state changes to `half-open`. This change is logged.
4. The circuit breaker tracks the next **10** calls to the failing endpoint. If more than **5** of them fail, return to step 1.
5. The internal state changes to `closed` and the endpoint is unblocked. The circuit breaker continues tracking requests to this endpoint. This change is logged.

**note:** In the `closed` state, the circuit breaker will evaluate the previous **100** requests in order to calculate the error rate. This means that at least **50** of them must have failed when the circuit breaker opens.

## Investigate Script Errors

If Custom API requests return errors of the type `custom-api-internal-server-error` or `custom-api-circuit-breaker-error`, use Log Center to investigate the cause.

1. In Business Manager, navigate to **Administration** > **Site Development** > **Development Setup**.
2. In the _Log Files_ section, click _Log Center_.
3. Select the Day of Year.
4. In the **LCQL** field, enter `CustomApiCircuitBreaker`.
5. In the query hits, look for a `CustomApiInvocationException` entry and click its **Stack Trace UUID** link.
6. In the stack trace, find the `Caused by` section. It can contain information about the cause of the failures. Some possible causes include:
- The script contains a remote call that never returns a response, causing the script execution to time out. In this case, try making an asynchronous call instead.
- The script contains errors. Fix the code and consider adding error handling measures.