Kubernetes provides a resource named ConfigMap to externalize the parameters to pass to your application in the form of key-value pairs or embedded application.properties or application.yaml files. The Spring Cloud Kubernetes Config project makes Kubernetes ConfigMap instances available during application bootstrapping and triggers hot reloading of beans or Spring context when changes are detected on observed ConfigMap instances.

The default behavior is to create a ConfigMapPropertySource based on a Kubernetes ConfigMap that has a metadata.name value of either the name of your Spring application (as defined by its spring.application.name property) or a custom name defined within the bootstrap.properties file under the following key: spring.cloud.kubernetes.config.name.

However, more advanced configuration is possible where you can use multiple ConfigMap instances. The spring.cloud.kubernetes.config.sources list makes this possible. For example, you could define the following ConfigMap instances:

spring:
  application:
    name: cloud-k8s-app
  cloud:
    kubernetes:
      config:
        name: default-name
        namespace: default-namespace
        sources:
         # Spring Cloud Kubernetes looks up a ConfigMap named c1 in namespace default-namespace
         - name: c1
         # Spring Cloud Kubernetes looks up a ConfigMap named default-name in whatever namespace n2
         - namespace: n2
         # Spring Cloud Kubernetes looks up a ConfigMap named c3 in namespace n3
         - namespace: n3
           name: c3

In the preceding example, if spring.cloud.kubernetes.config.namespace had not been set, the ConfigMap named c1 would be looked up in the namespace that the application runs.

Any matching ConfigMap that is found is processed as follows:

The single exception to the aforementioned flow is when the ConfigMap contains a single key that indicates the file is a YAML or properties file. In that case, the name of the key does NOT have to be application.yaml or application.properties (it can be anything) and the value of the property is treated correctly. This features facilitates the use case where the ConfigMap was created by using something like the following:

kubectl create configmap game-config --from-file=/path/to/app-config.yaml

Assume that we have a Spring Boot application named demo that uses the following properties to read its thread pool configuration.

This can be externalized to config map in yaml format as follows:

kind: ConfigMap
apiVersion: v1
metadata:
  name: demo
data:
  pool.size.core: 1
  pool.size.max: 16

Individual properties work fine for most cases. However, sometimes, embedded yaml is more convenient. In this case, we use a single property named application.yaml to embed our yaml, as follows:

kind: ConfigMap
apiVersion: v1
metadata:
  name: demo
data:
  application.yaml: |-
    pool:
      size:
        core: 1
        max:16

The following example also works:

kind: ConfigMap
apiVersion: v1
metadata:
  name: demo
data:
  custom-name.yaml: |-
    pool:
      size:
        core: 1
        max:16

You can also configure Spring Boot applications differently depending on active profiles that are merged together when the ConfigMap is read. You can provide different property values for different profiles by using an application.properties or application.yaml property, specifying profile-specific values, each in their own document (indicated by the --- sequence), as follows:

kind: ConfigMap
apiVersion: v1
metadata:
  name: demo
data:
  application.yml: |-
    greeting:
      message: Say Hello to the World
    farewell:
      message: Say Goodbye
    ---
    spring:
      profiles: development
    greeting:
      message: Say Hello to the Developers
    farewell:
      message: Say Goodbye to the Developers
    ---
    spring:
      profiles: production
    greeting:
      message: Say Hello to the Ops

In the preceding case, the configuration loaded into your Spring Application with the development profile is as follows:

  greeting:
    message: Say Hello to the Developers
  farewell:
    message: Say Goodbye to the Developers

However, if the production profile is active, the configuration becomes:

  greeting:
    message: Say Hello to the Ops
  farewell:
    message: Say Goodbye

If both profiles are active, the property that appears last within the ConfigMap overwrites any preceding values.

Another option is to create a different config map per profile and spring boot will automatically fetch it based on active profiles

kind: ConfigMap
apiVersion: v1
metadata:
  name: demo
data:
  application.yml: |-
    greeting:
      message: Say Hello to the World
    farewell:
      message: Say Goodbye

kind: ConfigMap
apiVersion: v1
metadata:
  name: demo-development
data:
  application.yml: |-
    spring:
      profiles: development
    greeting:
      message: Say Hello to the Developers
    farewell:
      message: Say Goodbye to the Developers

kind: ConfigMap
apiVersion: v1
metadata:
  name: demo-production
data:
  application.yml: |-
    spring:
      profiles: production
    greeting:
      message: Say Hello to the Ops
    farewell:
      message: Say Goodbye

To tell Spring Boot which profile should be enabled at bootstrap, you can pass a system property to the Java command. To do so, you can launch your Spring Boot application with an environment variable that you can define with the OpenShift DeploymentConfig or Kubernetes ReplicationConfig resource file, as follows:

apiVersion: v1
kind: DeploymentConfig
spec:
  replicas: 1
  ...
    spec:
      containers:
      - env:
        - name: JAVA_APP_DIR
          value: /deployments
        - name: JAVA_OPTIONS
          value: -Dspring.profiles.active=developer

	Note
	You should check the security configuration section. To access config maps from inside a pod you need to have the correct Kubernetes service accounts, roles and role bindings.

Another option for using ConfigMap instances is to mount them into the Pod by running the Spring Cloud Kubernetes application and having Spring Cloud Kubernetes read them from the file system. This behavior is controlled by the spring.cloud.kubernetes.config.paths property. You can use it in addition to or instead of the mechanism described earlier. You can specify multiple (exact) file paths in spring.cloud.kubernetes.config.paths by using the , delimiter.

	Note
	You have to provide the full exact path to each property file, because directories are not being recursively parsed.

Kubernetes has the notion of Secrets for storing sensitive data such as passwords, OAuth tokens, and so on. This project provides integration with Secrets to make secrets accessible by Spring Boot applications. You can explicitly enable or disable This feature by setting the spring.cloud.kubernetes.secrets.enabled property.

When enabled, the SecretsPropertySource looks up Kubernetes for Secrets from the following sources:

Note that, by default, consuming Secrets through the API (points 2 and 3 above) is not enabled for security reasons. Further, we recommend that containers share secrets through mounted volumes. If you enable consuming Secrets through the API, we recommend that you limit access to Secrets by using an [authorization policy, such as RBAC](https://kubernetes.io/docs/concepts/configuration/secret/#best-practices).

If the secrets are found, their data is made available to the application.

Assume that we have a spring boot application named demo that uses properties to read its database configuration. We can create a Kubernetes secret by using the following command:

oc create secret generic db-secret --from-literal=username=user --from-literal=password=p455w0rd

The preceding command would create the following secret (which you can see by using oc get secrets db-secret -o yaml):

apiVersion: v1
data:
  password: cDQ1NXcwcmQ=
  username: dXNlcg==
kind: Secret
metadata:
  creationTimestamp: 2017-07-04T09:15:57Z
  name: db-secret
  namespace: default
  resourceVersion: "357496"
  selfLink: /api/v1/namespaces/default/secrets/db-secret
  uid: 63c89263-6099-11e7-b3da-76d6186905a8
type: Opaque

Note that the data contains Base64-encoded versions of the literal provided by the create command.

Your application can then use this secret — for example, by exporting the secret’s value as environment variables:

apiVersion: v1
kind: Deployment
metadata:
  name: ${project.artifactId}
spec:
   template:
     spec:
       containers:
         - env:
            - name: DB_USERNAME
              valueFrom:
                 secretKeyRef:
                   name: db-secret
                   key: username
            - name: DB_PASSWORD
              valueFrom:
                 secretKeyRef:
                   name: db-secret
                   key: password

You can select the Secrets to consume in a number of ways:

Notes: * The spring.cloud.kubernetes.secrets.labels property behaves as defined by Map-based binding. * The spring.cloud.kubernetes.secrets.paths property behaves as defined by Collection-based binding. * Access to secrets through the API may be restricted for security reasons. The preferred way is to mount secrets to the Pod.

You can find an example of an application that uses secrets (though it has not been updated to use the new spring-cloud-kubernetes project) at spring-boot-camel-config

Some applications may need to detect changes on external property sources and update their internal status to reflect the new configuration. The reload feature of Spring Cloud Kubernetes is able to trigger an application reload when a related ConfigMap or Secret changes.

By default, this feature is disabled. You can enable it by using the spring.cloud.kubernetes.reload.enabled=true configuration property (for example, in the application.properties file).

The following levels of reload are supported (by setting the spring.cloud.kubernetes.reload.strategy property): * refresh (default): Only configuration beans annotated with @ConfigurationProperties or @RefreshScope are reloaded. This reload level leverages the refresh feature of Spring Cloud Context. * restart_context: the whole Spring ApplicationContext is gracefully restarted. Beans are recreated with the new configuration. * shutdown: the Spring ApplicationContext is shut down to activate a restart of the container. When you use this level, make sure that the lifecycle of all non-daemon threads is bound to the ApplicationContext and that a replication controller or replica set is configured to restart the pod.

Assuming that the reload feature is enabled with default settings (refresh mode), the following bean is refreshed when the config map changes:

@Configuration
@ConfigurationProperties(prefix = "bean")
public class MyConfig {

    private String message = "a message that can be changed live";

    // getter and setters

}

To see that changes effectively happen, you can create another bean that prints the message periodically, as follows

@Component
public class MyBean {

    @Autowired
    private MyConfig config;

    @Scheduled(fixedDelay = 5000)
    public void hello() {
        System.out.println("The message is: " + config.getMessage());
    }
}

You can change the message printed by the application by using a ConfigMap, as follows:

apiVersion: v1
kind: ConfigMap
metadata:
  name: reload-example
data:
  application.properties: |-
    bean.message=Hello World!

Any change to the property named bean.message in the ConfigMap associated with the pod is reflected in the output. More generally speaking, changes associated to properties prefixed with the value defined by the prefix field of the @ConfigurationProperties annotation are detected and reflected in the application. Associating a ConfigMap with a pod is explained earlier in this chapter.

The full example is available in spring-cloud-kubernetes-reload-example.

The reload feature supports two operating modes: * Event (default): Watches for changes in config maps or secrets by using the Kubernetes API (web socket). Any event produces a re-check on the configuration and, in case of changes, a reload. The view role on the service account is required in order to listen for config map changes. A higher level role (such as edit) is required for secrets (by default, secrets are not monitored). * Polling: Oeriodically re-creates the configuration from config maps and secrets to see if it has changed. You can configure the polling period by using the spring.cloud.kubernetes.reload.period property and defaults to 15 seconds. It requires the same role as the monitored property source. This means, for example, that using polling on file-mounted secret sources does not require particular privileges.

Notes: * You should not use properties under spring.cloud.kubernetes.reload in config maps or secrets. Changing such properties at runtime may lead to unexpected results. * Deleting a property or the whole config map does not restore the original state of the beans when you use the refresh level.

When the application runs as a pod inside Kubernetes, a Spring profile named kubernetes automatically gets activated. This lets you customize the configuration, to define beans that are applied when the Spring Boot application is deployed within the Kubernetes platform (for example, different development and production configuration).

When you include the spring-cloud-kubernetes-istio module in the application classpath, a new profile is added to the application, provided the application is running inside a Kubernetes Cluster with Istio installed. You can then use spring @Profile("istio") annotations in your Beans and @Configuration classes.

The Istio awareness module uses me.snowdrop:istio-client to interact with Istio APIs, letting us discover traffic rules, circuit breakers, and so on, making it easy for our Spring Boot applications to consume this data to dynamically configure themselves according to the environment.

Most of the components provided in this project need to know the namespace. For Kubernetes (1.3+), the namespace is made available to the pod as part of the service account secret and is automatically detected by the client. For earlier versions, it needs to be specified as an environment variable to the pod. A quick way to do this is as follows:

      env:
      - name: "KUBERNETES_NAMESPACE"
        valueFrom:
          fieldRef:
            fieldPath: "metadata.namespace"

For distributions of Kubernetes that support more fine-grained role-based access within the cluster, you need to make sure a pod that runs with spring-cloud-kubernetes has access to the Kubernetes API. For any service accounts you assign to a deployment or pod, you need to make sure they have the correct roles. For example, you can add cluster-reader permissions to your default service account, depending on the project you’re in.

To build the source you will need to install JDK 1.7.

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

	Note
	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.

	Note
	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.

For hints on how to build the project look in .travis.yml if there is one. There should be a "script" and maybe "install" command. Also look at the "services" section to see if any services need to be running locally (e.g. mongo or rabbit). Ignore the git-related bits that you might find in "before_install" since they’re related to setting git credentials and you already have those.

The projects that require middleware generally include a docker-compose.yml, so consider using Docker Compose to run the middeware servers in Docker containers. See the README in the scripts demo repository for specific instructions about the common cases of mongo, rabbit and redis.

	Note
	If all else fails, build with the command from .travis.yml (usually ./mvnw install).

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 ${basedir}, 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.

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.

14.3.1 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".

Note

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.

$ ./mvnw eclipse:eclipse

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.

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].

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.

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:

spring-cloud-build-tools/. 

└── src
    ├── checkstyle
    │   └── checkstyle-suppressions.xml 
    └── main
        └── resources
            ├── checkstyle-header.txt 
            └── checkstyle.xml 

<properties>
<maven-checkstyle-plugin.failsOnError>true</maven-checkstyle-plugin.failsOnError> 
        <maven-checkstyle-plugin.failsOnViolation>true
        </maven-checkstyle-plugin.failsOnViolation> 
        <maven-checkstyle-plugin.includeTestSourceDirectory>true
        </maven-checkstyle-plugin.includeTestSourceDirectory> 
</properties>

<build>
        <plugins>
            <plugin> 
                <groupId>io.spring.javaformat</groupId>
                <artifactId>spring-javaformat-maven-plugin</artifactId>
            </plugin>
            <plugin> 
                <groupId>org.apache.maven.plugins</groupId>
                <artifactId>maven-checkstyle-plugin</artifactId>
            </plugin>
        </plugins>

    <reporting>
        <plugins>
            <plugin> 
                <groupId>org.apache.maven.plugins</groupId>
                <artifactId>maven-checkstyle-plugin</artifactId>
            </plugin>
        </plugins>
    </reporting>
</build>

<?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>

$ curl https://raw.githubusercontent.com/spring-cloud/spring-cloud-build/master/.editorconfig -o .editorconfig
$ touch .springformat