import ballerina/http;
import ballerina/log;
import ballerina/runtime;
http:Client backendClientEP = new ("http://localhost:8080", {
circuitBreaker: {
rollingWindow: {
timeWindowInMillis: 10000,
bucketSizeInMillis: 2000,
requestVolumeThreshold: 0 },
failureThreshold: 0.2,
resetTimeInMillis: 10000,
statusCodes: [400, 404, 500] },
timeoutInMillis: 2000
}
);
@http:ServiceConfig {
basePath: "/cb"
}
service circuitbreaker on new http:Listener(9090) {
@http:ResourceConfig {
methods: ["GET"],
path: "/"
}
resource function invokeEndpoint(http:Caller caller, http:Request request) {
var backendResponse = backendClientEP->forward("/hello", request);
if (backendResponse is http:Response) {
var responseToCaller = caller->respond(backendResponse);
if (responseToCaller is http:ListenerError) {
log:printError("Error sending response", responseToCaller);
}
} else {
http:Response response = new;
response.statusCode = http:STATUS_INTERNAL_SERVER_ERROR;
response.setPayload(<string>backendResponse.detail()?.message);
var responseToCaller = caller->respond(response);
if (responseToCaller is http:ListenerError) {
log:printError("Error sending response", responseToCaller);
}
}
}
}int counter = 1;@http:ServiceConfig {
basePath: "/hello"
}
service helloWorld on new http:Listener(8080) {
@http:ResourceConfig {
methods: ["GET"],
path: "/"
}
resource function sayHello(http:Caller caller, http:Request req) {
if (counter % 5 == 0) {
runtime:sleep(5000); var result = caller->respond("Hello World!!!");
handleRespondResult(result);
} else if (counter % 5 == 3) {
http:Response res = new;
res.statusCode = 500;
res.setPayload(
"Internal error occurred while processing the request.");
var result = caller->respond(res);
handleRespondResult(result);
} else {
var result = caller->respond("Hello World!!!");
handleRespondResult(result);
}
counter = counter + 1;
}
}function handleRespondResult(error? result) {
if (result is http:ListenerError) {
log:printError("Error sending response from mock service", result);
}
}# To start the services, navigate to the directory that contains the
# `.bal` file and use the `ballerina run` command below.
ballerina run http_circuit_breaker.bal
[ballerina/http] started HTTP/WS listener 0.0.0.0:9090
[ballerina/http] started HTTP/WS listener 0.0.0.0:8080
2019-09-04 17:08:02,595 INFO [ballerina/http/resiliency] - CircuitBreaker failure threshold exceeded. Circuit tripped from CLOSE to OPEN state.
2019-09-04 17:08:12,514 INFO [ballerina/http/resiliency] - CircuitBreaker reset timeout reached. Circuit switched from OPEN to HALF_OPEN state.
2019-09-04 17:08:14,993 INFO [ballerina/http/resiliency] - CircuitBreaker trial run was successful. Circuit switched from HALF_OPEN to CLOSE state.
2019-09-04 17:08:20,003 ERROR [] - Error sending response from mock service : error {ballerina/http}GenericListenerError message=Connection between remote client and host is closed
2019-09-04 17:08:22,082 INFO [ballerina/http/resiliency] - CircuitBreaker failure threshold exceeded. Circuit tripped from CLOSE to OPEN state.
2019-09-04 17:08:32,755 INFO [ballerina/http/resiliency] - CircuitBreaker reset timeout reached. Circuit switched from OPEN to HALF_OPEN state.
2019-09-04 17:08:35,268 INFO [ballerina/http/resiliency] - CircuitBreaker trial run was successful. Circuit switched from HALF_OPEN to CLOSE state.# The first two requests complete without any errors.
curl -v http://localhost:9090/cb
* Trying ::1...
* TCP_NODELAY set
* Connected to localhost (::1) port 9090 (#0)
> GET /cb HTTP/1.1
> Host: localhost:9090
> User-Agent: curl/7.54.0
> Accept: */*
>
< HTTP/1.1 200 OK
< content-type: text/plain
< date: Wed, 4 Sep 2019 17:07:58 +0530
< server: ballerina/1.0.0-beta
< content-length: 14
<
* Connection #0 to host localhost left intact
Hello World!!!curl -v http://localhost:9090/cb
* Trying ::1...
* TCP_NODELAY set
* Connected to localhost (::1) port 9090 (#0)
> GET /cb HTTP/1.1
> Host: localhost:9090
> User-Agent: curl/7.54.0
> Accept: */*
>
< HTTP/1.1 200 OK
< content-type: text/plain
< date: Wed, 4 Sep 2019 17:08:00 +0530
< server: ballerina/1.0.0-beta
< content-length: 14
<
* Connection #0 to host localhost left intact
Hello World!!!# The third request responds with a `500 Internal Server Error` because the
# mock service sends a `500` http status code when responding to every third
# request.
curl -v http://localhost:9090/cb
* Trying ::1...
* TCP_NODELAY set
* Connected to localhost (::1) port 9090 (#0)
> GET /cb HTTP/1.1
> Host: localhost:9090
> User-Agent: curl/7.54.0
> Accept: */*
>
< HTTP/1.1 500 Internal Server Error
< content-type: text/plain
< date: Wed, 4 Sep 2019 17:08:00 +0530
< server: ballerina/1.0.0-beta
< content-length: 53
<
* Connection #0 to host localhost left intact
Internal error occurred while processing the request.# Subsequent requests fail immediately since the reset timeout period has not
# elapsed.
curl -v http://localhost:9090/cb
* Trying ::1...
* TCP_NODELAY set
* Connected to localhost (::1) port 9090 (#0)
> GET /cb HTTP/1.1
> Host: localhost:9090
> User-Agent: curl/7.54.0
> Accept: */*
>
< HTTP/1.1 500 Internal Server Error
< content-type: text/plain
< content-length: 99
< server: ballerina/1.0.0-beta
< date: Wed, 4 Sep 2019 17:08:02 +0530
<
* Connection #0 to host localhost left intact
Upstream service unavailable. Requests to upstream service will be suspended for 8340 milliseconds.curl -v http://localhost:9090/cb
* Trying ::1...
* TCP_NODELAY set
* Connected to localhost (::1) port 9090 (#0)
> GET /cb HTTP/1.1
> Host: localhost:9090
> User-Agent: curl/7.54.0
> Accept: */*
>
< HTTP/1.1 500 Internal Server Error
< content-type: text/plain
< content-length: 99
< server: ballerina/1.0.0-beta
< date: Wed, 4 Sep 2019 17:08:04 +0530
<
* Connection #0 to host localhost left intact
Upstream service unavailable. Requests to upstream service will be suspended for 6079 milliseconds.curl -v http://localhost:9090/cb
* Trying ::1...
* TCP_NODELAY set
* Connected to localhost (::1) port 9090 (#0)
> GET /cb HTTP/1.1
> Host: localhost:9090
> User-Agent: curl/7.54.0
> Accept: */*
>
< HTTP/1.1 500 Internal Server Error
< content-type: text/plain
< content-length: 99
< server: ballerina/1.0.0-beta
< date: Wed, 4 Sep 2019 17:08:07 +0530
<
* Connection #0 to host localhost left intact
Upstream service unavailable. Requests to upstream service will be suspended for 3475 milliseconds.# The request sent immediately after the timeout period expires, is the trial
# request. It is sent to see if the backend service is back to normal.
# If this request is successful, the circuit is set to `close` and normal
# functionality resumes.
curl -v http://localhost:9090/cb
* Trying ::1...
* TCP_NODELAY set
* Connected to localhost (::1) port 9090 (#0)
> GET /cb HTTP/1.1
> Host: localhost:9090
> User-Agent: curl/7.54.0
> Accept: */*
>
< HTTP/1.1 200 OK
< content-type: text/plain
< date: Wed, 4 Sep 2019 17:08:12 +0530
< server: ballerina/1.0.0-beta
< content-length: 14
<
* Connection #0 to host localhost left intact
Hello World!!!# The fifth request times out because the mock service times out when
# responding to every fifth request.
curl -v http://localhost:9090/cb
* Trying ::1...
* TCP_NODELAY set
* Connected to localhost (::1) port 9090 (#0)
> GET /cb HTTP/1.1
> Host: localhost:9090
> User-Agent: curl/7.54.0
> Accept: */*
>
< HTTP/1.1 500 Internal Server Error
< content-type: text/plain
< content-length: 57
< server: ballerina/1.0.0-beta
< date: Wed, 4 Sep 2019 17:08:17 +0530
<
* Connection #0 to host localhost left intact
Idle timeout triggered before initiating inbound response# Subsequent requests fail immediately since the reset timeout period has not
# elapsed.
curl -v http://localhost:9090/cb
* Trying ::1...
* TCP_NODELAY set
* Connected to localhost (::1) port 9090 (#0)
> GET /cb HTTP/1.1
> Host: localhost:9090
> User-Agent: curl/7.54.0
> Accept: */*
>
< HTTP/1.1 500 Internal Server Error
< content-type: text/plain
< content-length: 99
< server: ballerina/1.0.0-beta
< date: Wed, 4 Sep 2019 17:08:22 +0530
<
* Connection #0 to host localhost left intact
Upstream service unavailable. Requests to upstream service will be suspended for 4917 milliseconds.# The request sent immediately after the timeout period expires, is the trial
# request. It is sent to see if the backend service is back to normal.
# If this request is successful, the circuit is set to `close` and normal
# functionality resumes.
curl -v http://localhost:9090/cb
* Trying ::1...
* TCP_NODELAY set
* Connected to localhost (::1) port 9090 (#0)
> GET /cb HTTP/1.1
> Host: localhost:9090
> User-Agent: curl/7.54.0
> Accept: */*
>
< HTTP/1.1 200 OK
< content-type: text/plain
< date: Wed, 4 Sep 2019 17:08:32 +0530
< server: ballerina/1.0.0-beta
< content-length: 14
<
* Connection #0 to host localhost left intact
Hello World!!!# Since the immediate request after the timeout expired was successful, the
# requests sent after that complete normally.
curl -v http://localhost:9090/cb
* Trying ::1...
* TCP_NODELAY set
* Connected to localhost (::1) port 9090 (#0)
> GET /cb HTTP/1.1
> Host: localhost:9090
> User-Agent: curl/7.54.0
> Accept: */*
>
< HTTP/1.1 200 OK
< content-type: text/plain
< date: Wed, 4 Sep 2019 17:08:35 +0530
< server: ballerina/1.0.0-beta
< content-length: 14
<
* Connection #0 to host localhost left intact
Hello World!!!
Circuit BreakerThe Circuit Breaker is used to gracefully handle network related errors, which occur when using the HTTP Client. |
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The circuit breaker looks for errors across a rolling time window.
After the circuit is broken, it does not send requests to
the backend until the |
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Configuration options that control the behavior of the circuit breaker. |
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Failure calculation window. This is how long the circuit breaker keeps the statistics for the operations. |
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Time period in milliseconds for which the failure threshold is calculated. |
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The granularity (in milliseconds) at which the time window
slides.
The |
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Minimum number of requests in a |
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The threshold for request failures.
When this threshold exceeds, the circuit trips.
This is the ratio between failures and total requests and the
ratio is considered only within the configured |
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The time period (in milliseconds) to wait before attempting to
make another request to the upstream service.
When the failure threshold exceeds, the circuit trips to |
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HTTP response status codes that are considered as failures |
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Create an HTTP service bound to the endpoint (circuitBreakerEP). |
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Create a REST resource within the API. |
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The parameters include a reference to the caller and an object of the request data. |
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If the |
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This sample service is used to mock connection timeouts and service outages.
Mock a service outage by stopping/starting this service.
This should run separately from the |
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Delay the response by 5000 milliseconds to mimic the network level delays. |
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