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Added a circuit breaker handler using failsafe#64

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Merged
billoneil merged 2 commits intomasterfromf/failsafe-circuit-breaker-handler
Jan 29, 2018
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Original file line numberDiff line numberDiff line change
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package com.stubbornjava.common.undertow.handlers;

import org.slf4j.Logger;
import org.slf4j.LoggerFactory;

import io.undertow.server.HttpHandler;
import io.undertow.server.HttpServerExchange;
import net.jodah.failsafe.CircuitBreaker;
import net.jodah.failsafe.Failsafe;

// {{start:handler}}
public class CircuitBreakerHandler implements HttpHandler {
private static final Logger log = LoggerFactory.getLogger(CircuitBreakerHandler.class);

private final CircuitBreaker circuitBreaker;
private final HttpHandler delegate;
private final HttpHandler failureHandler;

public CircuitBreakerHandler(CircuitBreaker circuitBreaker, HttpHandler delegate, HttpHandler failureHandler) {
super();
this.circuitBreaker = circuitBreaker;
this.delegate = delegate;
this.failureHandler = failureHandler;
}

@Override
public void handleRequest(HttpServerExchange exchange) throws Exception {
Failsafe.with(circuitBreaker)
.withFallback(() -> failureHandler.handleRequest(exchange))
// We need to call get here instead of execute so we can return the
// mutated exchange to run checks on it
.get(() -> {
delegate.handleRequest(exchange);
return exchange;
});
}
}
// {{end:handler}}

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package com.stubbornjava.examples.failsafe;

import java.io.IOException;
import java.util.concurrent.Executors;
import java.util.concurrent.ScheduledExecutorService;
import java.util.concurrent.TimeUnit;

import org.slf4j.Logger;
import org.slf4j.LoggerFactory;

import com.stubbornjava.common.HttpClient;
import com.stubbornjava.common.undertow.Exchange;
import com.stubbornjava.common.undertow.SimpleServer;
import com.stubbornjava.common.undertow.handlers.CircuitBreakerHandler;
import com.stubbornjava.common.undertow.handlers.CustomHandlers;

import io.undertow.server.HttpHandler;
import io.undertow.server.HttpServerExchange;
import io.undertow.util.StatusCodes;
import net.jodah.failsafe.CircuitBreaker;
import okhttp3.HttpUrl;
import okhttp3.Request;

public class FailsafeWebserver {
private static final Logger log = LoggerFactory.getLogger(FailsafeWebserver.class);

// {{start:handlers}}
private static final void serverError(HttpServerExchange exchange) {
exchange.setStatusCode(StatusCodes.INTERNAL_SERVER_ERROR);
Exchange.body().sendText(exchange, "500 - Internal Server Error");
}

// This handler helps simulate errors, bad requests, and successful requests.
private static final void circuitClosed(HttpServerExchange exchange) {
boolean error = Exchange.queryParams().queryParamAsBoolean(exchange, "error").orElse(false);
boolean exception = Exchange.queryParams().queryParamAsBoolean(exchange, "exception").orElse(false);
if (error) {
exchange.setStatusCode(StatusCodes.BAD_REQUEST);
Exchange.body().sendText(exchange, "Bad Request");
} else if (exception) {
throw new RuntimeException("boom");
} else {
Exchange.body().sendText(exchange, "Circuit is open everything is functioning properly.");
}
}

private static final HttpHandler CIRCUIT_BREAKER_HANDLER;
static {
CircuitBreaker breaker = new CircuitBreaker()
// Trigger circuit breaker failure on exceptions or bad requests
.failIf((HttpServerExchange exchange, Throwable ex) -> {
return (exchange != null && StatusCodes.BAD_REQUEST == exchange.getStatusCode())
|| ex != null;
})
// If 7 out of 10 requests fail Open the circuit
.withFailureThreshold(7, 10)
// When half open if 3 out of 5 requests succeed close the circuit
.withSuccessThreshold(3, 5)
// Delay this long before half opening the circuit
.withDelay(2, TimeUnit.SECONDS)
.onClose(() -> log.info("Circuit Closed"))
.onOpen(() -> log.info("Circuit Opened"))
.onHalfOpen(() -> log.info("Circuit Half-Open"));

CIRCUIT_BREAKER_HANDLER = new CircuitBreakerHandler(breaker,
FailsafeWebserver::circuitClosed,
FailsafeWebserver::serverError);
}
// {{end:handlers}}

// {{start:request}}
private static void request(boolean error, boolean exception) {
HttpUrl url = HttpUrl.parse("http://localhost:8080")
.newBuilder()
.addQueryParameter("error", String.valueOf(error))
.addQueryParameter("exception", String.valueOf(exception))
.build();

Request request = new Request.Builder().get().url(url).build();
try {
log.info(HttpClient.globalClient().newCall(request).execute().body().string());
} catch (IOException e) {
e.printStackTrace();
}
}
// {{end:request}}

// {{start:main}}
public static void main(String[] args) {

HttpHandler exceptionHandler =
CustomHandlers.exception(CIRCUIT_BREAKER_HANDLER)
.addExceptionHandler(Throwable.class, FailsafeWebserver::serverError);

SimpleServer server = SimpleServer.simpleServer(exceptionHandler);
server.start();


// Warm-up the circuit breaker it needs to hit at least max executions
// Before it will reject anything. This will make that easier.
for (int i = 0; i < 10; i++) {
request(false, false);
}
ScheduledExecutorService schedExec = Executors.newScheduledThreadPool(1);

// A simple request that should always succeed
schedExec.scheduleAtFixedRate(() -> request(false, false), 0, 500, TimeUnit.MILLISECONDS);

// Send a batch of 15 bad requests to trigger the circuit breaker
Runnable errors = () -> {
log.info("Executing bad requests!");
for (int i = 0; i < 15; i++) {
request(true, false);
}
};
schedExec.schedule(errors, 1, TimeUnit.SECONDS);

// Send a batch of 15 requests that throw exceptions
Runnable exceptions = () -> {
log.info("Executing requests that throw exceptions!");
for (int i = 0; i < 15; i++) {
request(false, true);
}
};
schedExec.schedule(exceptions, 5, TimeUnit.SECONDS);
}
// {{end:main}}
}
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