Hystrix: Latency and Fault Tolerance for Distributed Systems

Hystrix Status

Hystrix is no longer in active development, and is currently in maintenance mode.

Hystrix (at version 1.5.18) is stable enough to meet the needs of Netflix for our existing applications. Meanwhile, our focus has shifted towards more adaptive implementations that react to an application’s real time performance rather than pre-configured settings (for example, through adaptive concurrency limits). For the cases where something like Hystrix makes sense, we intend to continue using Hystrix for existing applications, and to leverage open and active projects like resilience4j for new internal projects. We are beginning to recommend others do the same.

Netflix Hystrix is now officially in maintenance mode, with the following expectations to the greater community: Netflix will no longer actively review issues, merge pull-requests, and release new versions of Hystrix. We have made a final release of Hystrix (1.5.18) per issue 1891 so that the latest version in Maven Central is aligned with the last known stable version used internally at Netflix (1.5.11). If members of the community are interested in taking ownership of Hystrix and moving it back into active mode, please reach out to hystrixoss@googlegroups.com.

Hystrix has served Netflix and the community well over the years, and the transition to maintenance mode is in no way an indication that the concepts and ideas from Hystrix are no longer valuable. On the contrary, Hystrix has inspired many great ideas and projects. We thank everyone at Netflix, and in the greater community, for all the contributions made to Hystrix over the years.

Introduction

Hystrix is a latency and fault tolerance library designed to isolate points of access to remote systems, services and 3rd party libraries, stop cascading failure and enable resilience in complex distributed systems where failure is inevitable.

Full Documentation

See the Wiki for full documentation, examples, operational details and other information.

See the Javadoc for the API.

Communication

Google Group: HystrixOSS
Twitter: @HystrixOSS
GitHub Issues

What does it do?

1) Latency and Fault Tolerance

Stop cascading failures. Fallbacks and graceful degradation. Fail fast and rapid recovery.

Thread and semaphore isolation with circuit breakers.

2) Realtime Operations

Realtime monitoring and configuration changes. Watch service and property changes take effect immediately as they spread across a fleet.

Be alerted, make decisions, affect change and see results in seconds.

3) Concurrency

Parallel execution. Concurrency aware request caching. Automated batching through request collapsing.

Hello World!

Code to be isolated is wrapped inside the run() method of a HystrixCommand similar to the following:

public class CommandHelloWorld extends HystrixCommand<String> {

    private final String name;

    public CommandHelloWorld(String name) {
        super(HystrixCommandGroupKey.Factory.asKey("ExampleGroup"));
        this.name = name;
    }

    @Override
    protected String run() {
        return "Hello " + name + "!";
    }
}

This command could be used like this:

String s = new CommandHelloWorld("Bob").execute();
Future<String> s = new CommandHelloWorld("Bob").queue();
Observable<String> s = new CommandHelloWorld("Bob").observe();

More examples and information can be found in the How To Use section.

Example source code can be found in the hystrix-examples module.

Binaries

Binaries and dependency information for Maven, Ivy, Gradle and others can be found at http://search.maven.org.

Change history and version numbers => CHANGELOG.md

Example for Maven:

<dependency>
    <groupId>com.netflix.hystrix</groupId>
    <artifactId>hystrix-core</artifactId>
    <version>x.y.z</version>
</dependency>

and for Ivy:

<dependency org="com.netflix.hystrix" name="hystrix-core" rev="x.y.z" />

If you need to download the jars instead of using a build system, create a Maven pom file like this with the desired version:

<?xml version="1.0"?>
<project xmlns="http://maven.apache.org/POM/4.0.0" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xsi:schemaLocation="http://maven.apache.org/POM/4.0.0 http://maven.apache.org/xsd/maven-4.0.0.xsd">
	<modelVersion>4.0.0</modelVersion>
	<groupId>com.netflix.hystrix.download</groupId>
	<artifactId>hystrix-download</artifactId>
	<version>1.0-SNAPSHOT</version>
	<name>Simple POM to download hystrix-core and dependencies</name>
	<url>http://github.com/Netflix/Hystrix</url>
	<dependencies>
		<dependency>
			<groupId>com.netflix.hystrix</groupId>
			<artifactId>hystrix-core</artifactId>
			<version>x.y.z</version>
			<scope/>
		</dependency>
	</dependencies>
</project>

Then execute:

mvn -f download-hystrix-pom.xml dependency:copy-dependencies

It will download hystrix-core-*.jar and its dependencies into ./target/dependency/.

You need Java 6 or later.

Build

To build:

$ git clone git@github.com:Netflix/Hystrix.git
$ cd Hystrix/
$ ./gradlew build

Futher details on building can be found on the Getting Started page of the wiki.

Run Demo

To run a demo app do the following:

$ git clone git@github.com:Netflix/Hystrix.git
$ cd Hystrix/
./gradlew runDemo

You will see output similar to the following:

Request => GetUserAccountCommand[SUCCESS][8ms], GetPaymentInformationCommand[SUCCESS][20ms], GetUserAccountCommand[SUCCESS, RESPONSE_FROM_CACHE][0ms]x2, GetOrderCommand[SUCCESS][101ms], CreditCardCommand[SUCCESS][1075ms]
Request => GetUserAccountCommand[FAILURE, FALLBACK_SUCCESS][2ms], GetPaymentInformationCommand[SUCCESS][22ms], GetUserAccountCommand[FAILURE, FALLBACK_SUCCESS, RESPONSE_FROM_CACHE][0ms]x2, GetOrderCommand[SUCCESS][130ms], CreditCardCommand[SUCCESS][1050ms]
Request => GetUserAccountCommand[FAILURE, FALLBACK_SUCCESS][4ms], GetPaymentInformationCommand[SUCCESS][19ms], GetUserAccountCommand[FAILURE, FALLBACK_SUCCESS, RESPONSE_FROM_CACHE][0ms]x2, GetOrderCommand[SUCCESS][145ms], CreditCardCommand[SUCCESS][1301ms]
Request => GetUserAccountCommand[SUCCESS][4ms], GetPaymentInformationCommand[SUCCESS][11ms], GetUserAccountCommand[SUCCESS, RESPONSE_FROM_CACHE][0ms]x2, GetOrderCommand[SUCCESS][93ms], CreditCardCommand[SUCCESS][1409ms]

#####################################################################################
# CreditCardCommand: Requests: 17 Errors: 0 (0%)   Mean: 1171 75th: 1391 90th: 1470 99th: 1486 
# GetOrderCommand: Requests: 21 Errors: 0 (0%)   Mean: 100 75th: 144 90th: 207 99th: 230 
# GetUserAccountCommand: Requests: 21 Errors: 4 (19%)   Mean: 8 75th: 11 90th: 46 99th: 51 
# GetPaymentInformationCommand: Requests: 21 Errors: 0 (0%)   Mean: 18 75th: 21 90th: 24 99th: 25 
#####################################################################################

Request => GetUserAccountCommand[SUCCESS][10ms], GetPaymentInformationCommand[SUCCESS][16ms], GetUserAccountCommand[SUCCESS, RESPONSE_FROM_CACHE][0ms]x2, GetOrderCommand[SUCCESS][51ms], CreditCardCommand[SUCCESS][922ms]
Request => GetUserAccountCommand[SUCCESS][12ms], GetPaymentInformationCommand[SUCCESS][12ms], GetUserAccountCommand[SUCCESS, RESPONSE_FROM_CACHE][0ms]x2, GetOrderCommand[SUCCESS][68ms], CreditCardCommand[SUCCESS][1257ms]
Request => GetUserAccountCommand[SUCCESS][10ms], GetPaymentInformationCommand[SUCCESS][11ms], GetUserAccountCommand[SUCCESS, RESPONSE_FROM_CACHE][0ms]x2, GetOrderCommand[SUCCESS][78ms], CreditCardCommand[SUCCESS][1295ms]
Request => GetUserAccountCommand[FAILURE, FALLBACK_SUCCESS][6ms], GetPaymentInformationCommand[SUCCESS][11ms], GetUserAccountCommand[FAILURE, FALLBACK_SUCCESS, RESPONSE_FROM_CACHE][0ms]x2, GetOrderCommand[SUCCESS][153ms], CreditCardCommand[SUCCESS][1321ms]

This demo simulates 4 different HystrixCommand implementations with failures, latency, timeouts and duplicate calls in a multi-threaded environment.

It logs the results of HystrixRequestLog and metrics from HystrixCommandMetrics.

Dashboard

The hystrix-dashboard component of this project has been deprecated and moved to Netflix-Skunkworks/hystrix-dashboard. Please see the README there for more details including important security considerations.

Bugs and Feedback

For bugs, questions and discussions please use the GitHub Issues.

LICENSE

Licensed under the Apache License, Version 2.0 (the "License"); you may not use this file except in compliance with the License. You may obtain a copy of the License at

http://www.apache.org/licenses/LICENSE-2.0

Unless required by applicable law or agreed to in writing, software distributed under the License is distributed on an "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. See the License for the specific language governing permissions and limitations under the License.

dlmyL/Hystrix