2.1.5
1. Usage Documentation
The Spring Cloud CircuitBreaker project contains implementations for Resilience4J and Spring Retry. The APIs implemented in Spring Cloud CircuitBreaker live in Spring Cloud Commons. The usage documentation for these APIs are located in the Spring Cloud Commons documentation.
1.1. Configuring Resilience4J Circuit Breakers
1.1.1. Starters
There are two starters for the Resilience4J implementations, one for reactive applications and one for non-reactive applications.
-
org.springframework.cloud:spring-cloud-starter-circuitbreaker-resilience4j
- non-reactive applications -
org.springframework.cloud:spring-cloud-starter-circuitbreaker-reactor-resilience4j
- reactive applications
1.1.2. Auto-Configuration
You can disable the Resilience4J auto-configuration by setting
spring.cloud.circuitbreaker.resilience4j.enabled
to false
.
1.1.3. Default Configuration
To provide a default configuration for all of your circuit breakers create a Customize
bean that is passed a
Resilience4JCircuitBreakerFactory
or ReactiveResilience4JCircuitBreakerFactory
.
The configureDefault
method can be used to provide a default configuration.
@Bean
public Customizer<Resilience4JCircuitBreakerFactory> defaultCustomizer() {
return factory -> factory.configureDefault(id -> new Resilience4JConfigBuilder(id)
.timeLimiterConfig(TimeLimiterConfig.custom().timeoutDuration(Duration.ofSeconds(4)).build())
.circuitBreakerConfig(CircuitBreakerConfig.ofDefaults())
.build());
}
Reactive Example
@Bean
public Customizer<ReactiveResilience4JCircuitBreakerFactory> defaultCustomizer() {
return factory -> factory.configureDefault(id -> new Resilience4JConfigBuilder(id)
.circuitBreakerConfig(CircuitBreakerConfig.ofDefaults())
.timeLimiterConfig(TimeLimiterConfig.custom().timeoutDuration(Duration.ofSeconds(4)).build()).build());
}
1.1.4. Specific Circuit Breaker Configuration
Similarly to providing a default configuration, you can create a Customize
bean this is passed a
Resilience4JCircuitBreakerFactory
or ReactiveResilience4JCircuitBreakerFactory
.
@Bean
public Customizer<Resilience4JCircuitBreakerFactory> slowCustomizer() {
return factory -> factory.configure(builder -> builder.circuitBreakerConfig(CircuitBreakerConfig.ofDefaults())
.timeLimiterConfig(TimeLimiterConfig.custom().timeoutDuration(Duration.ofSeconds(2)).build()), "slow");
}
In addition to configuring the circuit breaker that is created you can also customize the circuit breaker after it has been created but before it is returned to the caller.
To do this you can use the addCircuitBreakerCustomizer
method.
This can be useful for adding event handlers to Resilience4J circuit breakers.
@Bean
public Customizer<Resilience4JCircuitBreakerFactory> slowCustomizer() {
return factory -> factory.addCircuitBreakerCustomizer(circuitBreaker -> circuitBreaker.getEventPublisher()
.onError(normalFluxErrorConsumer).onSuccess(normalFluxSuccessConsumer), "normalflux");
}
Reactive Example
@Bean
public Customizer<ReactiveResilience4JCircuitBreakerFactory> slowCustomizer() {
return factory -> {
factory.configure(builder -> builder
.timeLimiterConfig(TimeLimiterConfig.custom().timeoutDuration(Duration.ofSeconds(2)).build())
.circuitBreakerConfig(CircuitBreakerConfig.ofDefaults()), "slow", "slowflux");
factory.addCircuitBreakerCustomizer(circuitBreaker -> circuitBreaker.getEventPublisher()
.onError(normalFluxErrorConsumer).onSuccess(normalFluxSuccessConsumer), "normalflux");
};
}
1.1.5. Circuit Breaker Properties Configuration
You can configure CircuitBreaker
and TimeLimiter
instances in your application’s configuration properties file.
Property configuration has higher priority than Java Customizer
configuration.
resilience4j.circuitbreaker:
instances:
backendA:
registerHealthIndicator: true
slidingWindowSize: 100
backendB:
registerHealthIndicator: true
slidingWindowSize: 10
permittedNumberOfCallsInHalfOpenState: 3
slidingWindowType: TIME_BASED
recordFailurePredicate: io.github.robwin.exception.RecordFailurePredicate
resilience4j.timelimiter:
instances:
backendA:
timeoutDuration: 2s
cancelRunningFuture: true
backendB:
timeoutDuration: 1s
cancelRunningFuture: false
For more information on Resilience4j property configuration, see Resilience4J Spring Boot 2 Configuration.
1.1.6. Bulkhead pattern supporting
If resilience4j-bulkhead
is on the classpath, Spring Cloud CircuitBreaker will wrap all methods with a Resilience4j Bulkhead.
You can disable the Resilience4j Bulkhead by setting spring.cloud.circuitbreaker.bulkhead.resilience4j.enabled
to false
.
Spring Cloud CircuitBreaker Resilience4j provides two implementation of bulkhead pattern:
-
a
SemaphoreBulkhead
which uses Semaphores -
a
FixedThreadPoolBulkhead
which uses a bounded queue and a fixed thread pool.
By default, Spring Cloud CircuitBreaker Resilience4j uses FixedThreadPoolBulkhead
. To modify the default behavior to use SemaphoreBulkhead
set the property spring.cloud.circuitbreaker.resilience4j.enableSemaphoreDefaultBulkhead
to true
.
For more information on implementation of Bulkhead patterns see the Resilience4j Bulkhead.
The Customizer<Resilience4jBulkheadProvider>
can be used to provide a default Bulkhead
and ThreadPoolBulkhead
configuration.
@Bean
public Customizer<Resilience4jBulkheadProvider> defaultBulkheadCustomizer() {
return provider -> provider.configureDefault(id -> new Resilience4jBulkheadConfigurationBuilder()
.bulkheadConfig(BulkheadConfig.custom().maxConcurrentCalls(4).build())
.threadPoolBulkheadConfig(ThreadPoolBulkheadConfig.custom().coreThreadPoolSize(1).maxThreadPoolSize(1).build())
.build()
);
}
1.1.7. Specific Bulkhead Configuration
Similarly to proving a default 'Bulkhead' or 'ThreadPoolBulkhead' configuration, you can create a Customize
bean this
is passed a Resilience4jBulkheadProvider
.
@Bean
public Customizer<Resilience4jBulkheadProvider> slowBulkheadProviderCustomizer() {
return provider -> provider.configure(builder -> builder
.bulkheadConfig(BulkheadConfig.custom().maxConcurrentCalls(1).build())
.threadPoolBulkheadConfig(ThreadPoolBulkheadConfig.ofDefaults()), "slowBulkhead");
}
In addition to configuring the Bulkhead that is created you can also customize the bulkhead and thread pool bulkhead after they
have been created but before they are returned to caller. To do this you can use the addBulkheadCustomizer
and addThreadPoolBulkheadCustomizer
methods.
Bulkhead Example
@Bean
public Customizer<Resilience4jBulkheadProvider> customizer() {
return provider -> provider.addBulkheadCustomizer(bulkhead -> bulkhead.getEventPublisher()
.onCallRejected(slowRejectedConsumer)
.onCallFinished(slowFinishedConsumer), "slowBulkhead");
}
Thread Pool Bulkhead Example
@Bean
public Customizer<Resilience4jBulkheadProvider> slowThreadPoolBulkheadCustomizer() {
return provider -> provider.addThreadPoolBulkheadCustomizer(threadPoolBulkhead -> threadPoolBulkhead.getEventPublisher()
.onCallRejected(slowThreadPoolRejectedConsumer)
.onCallFinished(slowThreadPoolFinishedConsumer), "slowThreadPoolBulkhead");
}
1.1.8. Bulkhead Properties Configuration
You can configure ThreadPoolBulkhead and SemaphoreBulkhead instances in your application’s configuration properties file.
Property configuration has higher priority than Java Customizer
configuration.
resilience4j.thread-pool-bulkhead:
instances:
backendA:
maxThreadPoolSize: 1
coreThreadPoolSize: 1
resilience4j.bulkhead:
instances:
backendB:
maxConcurrentCalls: 10
For more inforamtion on the Resilience4j property configuration, see Resilience4J Spring Boot 2 Configuration.
1.1.9. Collecting Metrics
Spring Cloud Circuit Breaker Resilience4j includes auto-configuration to setup metrics collection as long as the right
dependencies are on the classpath. To enable metric collection you must include org.springframework.boot:spring-boot-starter-actuator
, and io.github.resilience4j:resilience4j-micrometer
. For more information on the metrics that
get produced when these dependencies are present, see the Resilience4j documentation.
You don’t have to include micrometer-core directly as it is brought in by spring-boot-starter-actuator
|
1.2. Configuring Spring Retry Circuit Breakers
Spring Retry provides declarative retry support for Spring applications.
A subset of the project includes the ability to implement circuit breaker functionality.
Spring Retry provides a circuit breaker implementation via a combination of it’s
CircuitBreakerRetryPolicy
and a stateful retry.
All circuit breakers created using Spring Retry will be created using the CircuitBreakerRetryPolicy
and a
DefaultRetryState
.
Both of these classes can be configured using SpringRetryConfigBuilder
.
1.2.1. Default Configuration
To provide a default configuration for all of your circuit breakers create a Customize
bean that is passed a
SpringRetryCircuitBreakerFactory
.
The configureDefault
method can be used to provide a default configuration.
@Bean
public Customizer<SpringRetryCircuitBreakerFactory> defaultCustomizer() {
return factory -> factory.configureDefault(id -> new SpringRetryConfigBuilder(id)
.retryPolicy(new TimeoutRetryPolicy()).build());
}
1.2.2. Specific Circuit Breaker Configuration
Similarly to providing a default configuration, you can create a Customize
bean this is passed a
SpringRetryCircuitBreakerFactory
.
@Bean
public Customizer<SpringRetryCircuitBreakerFactory> slowCustomizer() {
return factory -> factory.configure(builder -> builder.retryPolicy(new SimpleRetryPolicy(1)).build(), "slow");
}
In addition to configuring the circuit breaker that is created you can also customize the circuit breaker after it has been created but before it is returned to the caller.
To do this you can use the addRetryTemplateCustomizers
method.
This can be useful for adding event handlers to the RetryTemplate
.
@Bean
public Customizer<SpringRetryCircuitBreakerFactory> slowCustomizer() {
return factory -> factory.addRetryTemplateCustomizers(retryTemplate -> retryTemplate.registerListener(new RetryListener() {
@Override
public <T, E extends Throwable> boolean open(RetryContext context, RetryCallback<T, E> callback) {
return false;
}
@Override
public <T, E extends Throwable> void close(RetryContext context, RetryCallback<T, E> callback, Throwable throwable) {
}
@Override
public <T, E extends Throwable> void onError(RetryContext context, RetryCallback<T, E> callback, Throwable throwable) {
}
}));
}
2. Building
2.1. Basic Compile and Test
To build the source you will need to install JDK 17.
Spring Cloud uses Maven for most build-related activities, and you should be able to get off the ground quite quickly by cloning the project you are interested in and typing
$ ./mvnw install
You can also install Maven (>=3.3.3) yourself and run the mvn command
in place of ./mvnw in the examples below. If you do that you also
might need to add -P spring if your local Maven settings do not
contain repository declarations for spring pre-release artifacts.
|
Be aware that you might need to increase the amount of memory
available to Maven by setting a MAVEN_OPTS environment variable with
a value like -Xmx512m -XX:MaxPermSize=128m . We try to cover this in
the .mvn configuration, so if you find you have to do it to make a
build succeed, please raise a ticket to get the settings added to
source control.
|
The projects that require middleware (i.e. Redis) for testing generally require that a local instance of [Docker](www.docker.com/get-started) is installed and running.
2.2. Documentation
The spring-cloud-build module has a "docs" profile, and if you switch
that on it will try to build asciidoc sources from
src/main/asciidoc
. As part of that process it will look for a
README.adoc
and process it by loading all the includes, but not
parsing or rendering it, just copying it to ${main.basedir}
(defaults to $/tmp/releaser-1667489304382-0/spring-cloud-circuitbreaker/docs
, i.e. the root of the project). If there are
any changes in the README it will then show up after a Maven build as
a modified file in the correct place. Just commit it and push the change.
2.3. Working with the code
If you don’t have an IDE preference we would recommend that you use Spring Tools Suite or Eclipse when working with the code. We use the m2eclipse eclipse plugin for maven support. Other IDEs and tools should also work without issue as long as they use Maven 3.3.3 or better.
2.3.1. Activate the Spring Maven profile
Spring Cloud projects require the 'spring' Maven profile to be activated to resolve the spring milestone and snapshot repositories. Use your preferred IDE to set this profile to be active, or you may experience build errors.
2.3.2. Importing into eclipse with m2eclipse
We recommend the m2eclipse eclipse plugin when working with eclipse. If you don’t already have m2eclipse installed it is available from the "eclipse marketplace".
Older versions of m2e do not support Maven 3.3, so once the
projects are imported into Eclipse you will also need to tell
m2eclipse to use the right profile for the projects. If you
see many different errors related to the POMs in the projects, check
that you have an up to date installation. If you can’t upgrade m2e,
add the "spring" profile to your settings.xml . Alternatively you can
copy the repository settings from the "spring" profile of the parent
pom into your settings.xml .
|
2.3.3. Importing into eclipse without m2eclipse
If you prefer not to use m2eclipse you can generate eclipse project metadata using the following command:
$ ./mvnw eclipse:eclipse
The generated eclipse projects can be imported by selecting import existing projects
from the file
menu.
3. Contributing
Spring Cloud is released under the non-restrictive Apache 2.0 license, and follows a very standard Github development process, using Github tracker for issues and merging pull requests into master. If you want to contribute even something trivial please do not hesitate, but follow the guidelines below.
3.1. Sign the Contributor License Agreement
Before we accept a non-trivial patch or pull request we will need you to sign the Contributor License Agreement. Signing the contributor’s agreement does not grant anyone commit rights to the main repository, but it does mean that we can accept your contributions, and you will get an author credit if we do. Active contributors might be asked to join the core team, and given the ability to merge pull requests.
3.2. Code of Conduct
This project adheres to the Contributor Covenant code of conduct. By participating, you are expected to uphold this code. Please report unacceptable behavior to [email protected].
3.3. Code Conventions and Housekeeping
None of these is essential for a pull request, but they will all help. They can also be added after the original pull request but before a merge.
-
Use the Spring Framework code format conventions. If you use Eclipse you can import formatter settings using the
eclipse-code-formatter.xml
file from the Spring Cloud Build project. If using IntelliJ, you can use the Eclipse Code Formatter Plugin to import the same file. -
Make sure all new
.java
files to have a simple Javadoc class comment with at least an@author
tag identifying you, and preferably at least a paragraph on what the class is for. -
Add the ASF license header comment to all new
.java
files (copy from existing files in the project) -
Add yourself as an
@author
to the .java files that you modify substantially (more than cosmetic changes). -
Add some Javadocs and, if you change the namespace, some XSD doc elements.
-
A few unit tests would help a lot as well — someone has to do it.
-
If no-one else is using your branch, please rebase it against the current master (or other target branch in the main project).
-
When writing a commit message please follow these conventions, if you are fixing an existing issue please add
Fixes gh-XXXX
at the end of the commit message (where XXXX is the issue number).
3.4. Checkstyle
Spring Cloud Build comes with a set of checkstyle rules. You can find them in the spring-cloud-build-tools
module. The most notable files under the module are:
└── src ├── checkstyle │ └── checkstyle-suppressions.xml (3) └── main └── resources ├── checkstyle-header.txt (2) └── checkstyle.xml (1)
1 | Default Checkstyle rules |
2 | File header setup |
3 | Default suppression rules |
3.4.1. Checkstyle configuration
Checkstyle rules are disabled by default. To add checkstyle to your project just define the following properties and plugins.
<properties> <maven-checkstyle-plugin.failsOnError>true</maven-checkstyle-plugin.failsOnError> (1) <maven-checkstyle-plugin.failsOnViolation>true </maven-checkstyle-plugin.failsOnViolation> (2) <maven-checkstyle-plugin.includeTestSourceDirectory>true </maven-checkstyle-plugin.includeTestSourceDirectory> (3) </properties> <build> <plugins> <plugin> (4) <groupId>io.spring.javaformat</groupId> <artifactId>spring-javaformat-maven-plugin</artifactId> </plugin> <plugin> (5) <groupId>org.apache.maven.plugins</groupId> <artifactId>maven-checkstyle-plugin</artifactId> </plugin> </plugins> <reporting> <plugins> <plugin> (5) <groupId>org.apache.maven.plugins</groupId> <artifactId>maven-checkstyle-plugin</artifactId> </plugin> </plugins> </reporting> </build>
1 | Fails the build upon Checkstyle errors |
2 | Fails the build upon Checkstyle violations |
3 | Checkstyle analyzes also the test sources |
4 | Add the Spring Java Format plugin that will reformat your code to pass most of the Checkstyle formatting rules |
5 | Add checkstyle plugin to your build and reporting phases |
If you need to suppress some rules (e.g. line length needs to be longer), then it’s enough for you to define a file under ${project.root}/src/checkstyle/checkstyle-suppressions.xml
with your suppressions. Example:
<?xml version="1.0"?> <!DOCTYPE suppressions PUBLIC "-//Puppy Crawl//DTD Suppressions 1.1//EN" "https://www.puppycrawl.com/dtds/suppressions_1_1.dtd"> <suppressions> <suppress files=".*ConfigServerApplication\.java" checks="HideUtilityClassConstructor"/> <suppress files=".*ConfigClientWatch\.java" checks="LineLengthCheck"/> </suppressions>
It’s advisable to copy the ${spring-cloud-build.rootFolder}/.editorconfig
and ${spring-cloud-build.rootFolder}/.springformat
to your project. That way, some default formatting rules will be applied. You can do so by running this script:
$ curl https://raw.githubusercontent.com/spring-cloud/spring-cloud-build/master/.editorconfig -o .editorconfig
$ touch .springformat
3.5. IDE setup
3.5.1. Intellij IDEA
In order to setup Intellij you should import our coding conventions, inspection profiles and set up the checkstyle plugin. The following files can be found in the Spring Cloud Build project.
└── src ├── checkstyle │ └── checkstyle-suppressions.xml (3) └── main └── resources ├── checkstyle-header.txt (2) ├── checkstyle.xml (1) └── intellij ├── Intellij_Project_Defaults.xml (4) └── Intellij_Spring_Boot_Java_Conventions.xml (5)
1 | Default Checkstyle rules |
2 | File header setup |
3 | Default suppression rules |
4 | Project defaults for Intellij that apply most of Checkstyle rules |
5 | Project style conventions for Intellij that apply most of Checkstyle rules |
![Code style](https://raw.githubusercontent.com/spring-cloud/spring-cloud-build/master/docs/src/main/asciidoc/images/intellij-code-style.png)
Go to File
→ Settings
→ Editor
→ Code style
. There click on the icon next to the Scheme
section. There, click on the Import Scheme
value and pick the Intellij IDEA code style XML
option. Import the spring-cloud-build-tools/src/main/resources/intellij/Intellij_Spring_Boot_Java_Conventions.xml
file.
![Code style](https://raw.githubusercontent.com/spring-cloud/spring-cloud-build/master/docs/src/main/asciidoc/images/intellij-inspections.png)
Go to File
→ Settings
→ Editor
→ Inspections
. There click on the icon next to the Profile
section. There, click on the Import Profile
and import the spring-cloud-build-tools/src/main/resources/intellij/Intellij_Project_Defaults.xml
file.
To have Intellij work with Checkstyle, you have to install the Checkstyle
plugin. It’s advisable to also install the Assertions2Assertj
to automatically convert the JUnit assertions
![Checkstyle](https://raw.githubusercontent.com/spring-cloud/spring-cloud-build/master/docs/src/main/asciidoc/images/intellij-checkstyle.png)
Go to File
→ Settings
→ Other settings
→ Checkstyle
. There click on the +
icon in the Configuration file
section. There, you’ll have to define where the checkstyle rules should be picked from. In the image above, we’ve picked the rules from the cloned Spring Cloud Build repository. However, you can point to the Spring Cloud Build’s GitHub repository (e.g. for the checkstyle.xml
: raw.githubusercontent.com/spring-cloud/spring-cloud-build/master/spring-cloud-build-tools/src/main/resources/checkstyle.xml
). We need to provide the following variables:
-
checkstyle.header.file
- please point it to the Spring Cloud Build’s,spring-cloud-build-tools/src/main/resources/checkstyle-header.txt
file either in your cloned repo or via theraw.githubusercontent.com/spring-cloud/spring-cloud-build/master/spring-cloud-build-tools/src/main/resources/checkstyle-header.txt
URL. -
checkstyle.suppressions.file
- default suppressions. Please point it to the Spring Cloud Build’s,spring-cloud-build-tools/src/checkstyle/checkstyle-suppressions.xml
file either in your cloned repo or via theraw.githubusercontent.com/spring-cloud/spring-cloud-build/master/spring-cloud-build-tools/src/checkstyle/checkstyle-suppressions.xml
URL. -
checkstyle.additional.suppressions.file
- this variable corresponds to suppressions in your local project. E.g. you’re working onspring-cloud-contract
. Then point to theproject-root/src/checkstyle/checkstyle-suppressions.xml
folder. Example forspring-cloud-contract
would be:/home/username/spring-cloud-contract/src/checkstyle/checkstyle-suppressions.xml
.
Remember to set the Scan Scope to All sources since we apply checkstyle rules for production and test sources.
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3.6. Duplicate Finder
Spring Cloud Build brings along the basepom:duplicate-finder-maven-plugin
, that enables flagging duplicate and conflicting classes and resources on the java classpath.
3.6.1. Duplicate Finder configuration
Duplicate finder is enabled by default and will run in the verify
phase of your Maven build, but it will only take effect in your project if you add the duplicate-finder-maven-plugin
to the build
section of the projecst’s pom.xml
.
<build>
<plugins>
<plugin>
<groupId>org.basepom.maven</groupId>
<artifactId>duplicate-finder-maven-plugin</artifactId>
</plugin>
</plugins>
</build>
For other properties, we have set defaults as listed in the plugin documentation.
You can easily override them but setting the value of the selected property prefixed with duplicate-finder-maven-plugin
. For example, set duplicate-finder-maven-plugin.skip
to true
in order to skip duplicates check in your build.
If you need to add ignoredClassPatterns
or ignoredResourcePatterns
to your setup, make sure to add them in the plugin configuration section of your project:
<build>
<plugins>
<plugin>
<groupId>org.basepom.maven</groupId>
<artifactId>duplicate-finder-maven-plugin</artifactId>
<configuration>
<ignoredClassPatterns>
<ignoredClassPattern>org.joda.time.base.BaseDateTime</ignoredClassPattern>
<ignoredClassPattern>.*module-info</ignoredClassPattern>
</ignoredClassPatterns>
<ignoredResourcePatterns>
<ignoredResourcePattern>changelog.txt</ignoredResourcePattern>
</ignoredResourcePatterns>
</configuration>
</plugin>
</plugins>
</build>