Circuit Breaker

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 Breaker

The Circuit Breaker is used to gracefully handle network related errors, which occur when using the HTTP Client.

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Load Balancing

`import ballerina/http; import ballerina/log; import ballerina/runtime;`
`http:Client backendClientEP = new ("http://localhost:8080", {`	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 `resetTime`.
`circuitBreaker: {`	Configuration options that control the behavior of the circuit breaker.
`rollingWindow: {`	Failure calculation window. This is how long the circuit breaker keeps the statistics for the operations.
`timeWindowInMillis: 10000,`	Time period in milliseconds for which the failure threshold is calculated.
`bucketSizeInMillis: 2000,`	The granularity (in milliseconds) at which the time window slides. The `RollingWindow` is divided into buckets and slides by these increments. For an example, if this `timeWindowInMillis` is set to 10000 milliseconds and `bucketSizeInMillis` 2000, then `RollingWindow` breaks into sub windows with 2-second buckets. Stats are collected with respect to the buckets. As time rolls, a new bucket will be appended to the end of the window and the old bucket will be removed.
`requestVolumeThreshold: 0`	Minimum number of requests in a `RollingWindow` that will trip the circuit.
`},`
`failureThreshold: 0.2,`	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 `RollingWindow`.
`resetTimeInMillis: 10000,`	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 `OPEN` state. Once the circuit is in `OPEN` state circuit breaker waits for the time configured in `resetTimeInMillis` and switch the circuit to the `HALF_OPEN` state.
`statusCodes: [400, 404, 500]`	HTTP response status codes that are considered as failures
`}, timeoutInMillis: 2000 } );`
`@http:ServiceConfig { basePath: "/cb" } service circuitbreaker on new http:Listener(9090) {`	Create an HTTP service bound to the endpoint (circuitBreakerEP).
`@http:ResourceConfig { methods: ["GET"], path: "/" }`	Create a REST resource within the API.
`resource function invokeEndpoint(http:Caller caller, http:Request request) { var backendResponse = backendClientEP->forward("/hello", request);`	The parameters include a reference to the caller and an object of the request data.
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); } } } }	If the `backendResponse` is an `http:Response`, it is sent back to the client. If `backendResponse` is an `http:ClientError`, an internal server error is returned to the client.
`int counter = 1;`
	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 `circuitBreakerDemo` service.
`@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);`	Delay the response by 5000 milliseconds to mimic the network level delays.
`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 Breaker

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