Spring Cloud Kubernetes provides implementations of well known Spring Cloud interfaces allowing developers to build and run Spring Cloud applications on Kubernetes. While this project may be useful to you when building a cloud native application, it is also not a requirement in order to deploy a Spring Boot app on Kubernetes. If you are just getting started in your journey to running your Spring Boot app on Kubernetes you can accomplish a lot with nothing more than a basic Spring Boot app and Kubernetes itself. To learn more, you can get started by reading the Spring Boot reference documentation for deploying to Kubernetes and also working through the workshop material Spring and Kubernetes .

Starters are convenient dependency descriptors you can include in your application. Include a starter to get the dependencies and Spring Boot auto-configuration for a feature set. Starters that begin with spring-cloud-starter-kubernetes-fabric8 provide implementations using the Fabric8 Kubernetes Java Client . Starters that begin with spring-cloud-starter-kubernetes-client provide implementations using the Kubernetes Java Client .

<dependency>
    <groupId>org.springframework.cloud</groupId>
    <artifactId>spring-cloud-starter-kubernetes-fabric8</artifactId>
</dependency>

<dependency>
    <groupId>org.springframework.cloud</groupId>
    <artifactId>spring-cloud-starter-kubernetes-client</artifactId>
</dependency>

Discovery Client implementation that resolves service names to Kubernetes Services.

<dependency>
    <groupId>org.springframework.cloud</groupId>
    <artifactId>spring-cloud-starter-kubernetes-fabric8-config</artifactId>
</dependency>

<dependency>
    <groupId>org.springframework.cloud</groupId>
    <artifactId>spring-cloud-starter-kubernetes-client-config</artifactId>
</dependency>

Load application properties from Kubernetes ConfigMaps and Secrets . Reload application properties when a ConfigMap or Secret changes.

<dependency>
    <groupId>org.springframework.cloud</groupId>
    <artifactId>spring-cloud-starter-kubernetes-fabric8-all</artifactId>
</dependency>

<dependency>
    <groupId>org.springframework.cloud</groupId>
    <artifactId>spring-cloud-starter-kubernetes-client-all</artifactId>
</dependency>

All Spring Cloud Kubernetes features.

This project provides an implementation of Discovery Client for Kubernetes . This client lets you query Kubernetes endpoints (see services ) by name. A service is typically exposed by the Kubernetes API server as a collection of endpoints that represent http and https addresses and that a client can access from a Spring Boot application running as a pod.

DiscoveryClient can also find services of type ExternalName (see ExternalName services ). At the moment, external name support type of services is only available if the following property spring.cloud.kubernetes.discovery.include-external-name-services is set to true and only in the fabric8 implementation. In a later release, support will be added for the kubernetes native client also.

This is something that you get for free by adding the following dependency inside your project:

<dependency>
    <groupId>org.springframework.cloud</groupId>
    <artifactId>spring-cloud-starter-kubernetes-discoveryclient</artifactId>
</dependency>

<dependency>
    <groupId>org.springframework.cloud</groupId>
    <artifactId>spring-cloud-starter-kubernetes-fabric8</artifactId>
</dependency>

<dependency>
    <groupId>org.springframework.cloud</groupId>
    <artifactId>spring-cloud-starter-kubernetes-client</artifactId>
</dependency>

If your service exposes multiple ports, you will need to specify which port the DiscoveryClient should use. The DiscoveryClient will choose the port using the following logic.

If the service has a label primary-port-name it will use the port with the name specified in the label’s value.

If no label is present, then the port name specified in spring.cloud.kubernetes.discovery.primary-port-name will be used.

If neither of the above are specified it will use the port named https .

If none of the above conditions are met it will use the port named http .

As a last resort it wil pick the first port in the list of ports.

By default all of the ports and their names will be added to the metadata of the ServiceInstance .

As said before, if you want to get the list of ServiceInstance to also include the ExternalName type services, you need to enable that support via: spring.cloud.kubernetes.discovery.include-external-name-services=true . As such, when calling DiscoveryClient::getInstances those will be returned also. You can distinguish between ExternalName and any other types by inspecting ServiceInstance::getMetadata and lookup for a field called type . This will be the type of the service returned : ExternalName / ClusterIP , etc.

ServiceInstance can include the labels and annotations of specific pods from the underlying service instance. To obtain such information, you need to also enable:

spring.cloud.kubernetes.discovery.metadata.add-pod-labels=true and/or spring.cloud.kubernetes.discovery.metadata.add-pod-annotations=true . At the moment, such functionality is present only in the fabric8 client implementation, but will be added to the kubernetes native client in a later release.

If, for any reason, you need to disable the DiscoveryClient , you can set the following property in application.properties :

Some Spring Cloud components use the DiscoveryClient in order to obtain information about the local service instance. For this to work, you need to align the Kubernetes service name with the spring.application.name property.

Spring Cloud Kubernetes can also watch the Kubernetes service catalog for changes and update the DiscoveryClient implementation accordingly. By "watch" we mean that we will publish a heartbeat event every spring.cloud.kubernetes.discovery.catalog-services-watch-delay milliseconds (by default it is 30000 ). The heartbeat event will contain the target references (and their namespaces of the addresses of all endpoints (for the exact details of what will get returned you can take a look inside KubernetesCatalogWatch ). This is an implementation detail, and listeners of the heartbeat event should not rely on the details. Instead, they should see if there are differences between two subsequent heartbeats via equals method. We will take care to return a correct implementation that adheres to the equals contract. The endpoints will be queried in either :

In order to enable this functionality you need to add @EnableScheduling on a configuration class in your application.

By default, we use the Endpoints (see kubernetes.io/docs/concepts/services-networking/service/#endpoints ) API to find out the current state of services. There is another way though, via EndpointSlices ( kubernetes.io/docs/concepts/services-networking/endpoint-slices/ ). Such support can be enabled via a property: spring.cloud.kubernetes.discovery.use-endpoint-slices=true (by default it is false ). Of course, your cluster has to support it also. As a matter of fact, if you enable this property, but your cluster does not support it, we will fail starting the application. If you decide to enable such support, you also need proper Role/ClusterRole set-up. For example:

apiVersion: rbac.authorization.k8s.io/v1
kind: Role
metadata:
  namespace: default
  name: namespace-reader
rules:
  - apiGroups: ["discovery.k8s.io"]
    resources: ["endpointslices"]
    verbs: ["get", "list", "watch"]

Kubernetes itself is capable of (server side) service discovery (see: kubernetes.io/docs/concepts/services-networking/service/#discovering-services ). Using native kubernetes service discovery ensures compatibility with additional tooling, such as Istio ( istio.io ), a service mesh that is capable of load balancing, circuit breaker, failover, and much more.

The caller service then need only refer to names resolvable in a particular Kubernetes cluster. A simple implementation might use a spring RestTemplate that refers to a fully qualified domain name (FQDN), such as {service-name}.{namespace}.svc.{cluster}.local:{service-port} .

Additionally, you can use Hystrix for:

Circuit breaker implementation on the caller side, by annotating the spring boot application class with @EnableCircuitBreaker

Fallback functionality, by annotating the respective method with @HystrixCommand(fallbackMethod=

The most common approach to configuring your Spring Boot application is to create an application.properties or application.yaml or an application-profile.properties or application-profile.yaml file that contains key-value pairs that provide customization values to your application or Spring Boot starters. You can override these properties by specifying system properties or environment variables.

To enable this functionality you need to set spring.config.import=kubernetes: in your application’s configuration properties. Currently you can not specify a ConfigMap or Secret to load using spring.config.import , by default Spring Cloud Kubernetes will load a ConfigMap and/or Secret based on the spring.application.name property. If spring.application.name is not set it will load a ConfigMap and/or Secret with the name application .

If you would like to load Kubernetes PropertySource s during the bootstrap phase like it worked prior to the 3.0.x release you can either add spring-cloud-starter-bootstrap to your application’s classpath or set spring.cloud.bootstrap.enabled=true as an environment variable.

5.1. Using a ConfigMap PropertySource

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 startup and triggers hot reloading of beans or Spring context when changes are detected on observed ConfigMap instances.

Everything that follows is explained mainly referring to examples using ConfigMaps, but the same stands for Secrets, i.e.: every feature is supported for both.

The default behavior is to create a Fabric8ConfigMapPropertySource (or a KubernetesClientConfigMapPropertySource ) 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 application.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:

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. See Namespace resolution to get a better understanding of how the namespace of the application is resolved.

Any matching ConfigMap that is found is processed as follows:

Apply as yaml (or properties ) the content of any property that is named by the value of spring.application.name (if it’s not present, by application.yaml/properties )

Apply as a properties file the content of the above name + each active profile.

An example should make a lot more sense. Let’s suppose that spring.application.name=my-app and that we have a single active profile called k8s . For a configuration as below:

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:

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

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:

This will search for every configmap in namespace spring-k8s that has labels {letter : a} . The important thing to notice here is that unlike reading a configmap by name, this can result in multiple config maps read. As usual, the same feature is supported for secrets.

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:

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

To tell Spring Boot which profile should be enabled see the Spring Boot documentation . One option for activating a specific profile when deploying to Kubernetes is to launch your Spring Boot application with an environment variable that you can define in the PodSpec at the container specification. Deployment resource file, as follows:

Notice that spring.cloud.kubernetes.config.useNameAsPrefix has a lower priority than spring.cloud.kubernetes.config.sources.useNameAsPrefix . This allows you to set a "default" strategy for all sources, at the same time allowing to override only a few.

If using the config map name is not an option, you can specify a different strategy, called : explicitPrefix . Since this is an explicit prefix that you select, it can only be supplied to the sources level. At the same time it has a higher priority than useNameAsPrefix . Let’s suppose we have a third config map with these entries:

The same way you configure a prefix for configmaps, you can do it for secrets also; both for secrets that are based on name and the ones based on labels. For example:

The same processing rules apply when generating property source as for config maps. The only difference is that potentially, looking up secrets by labels can mean that we find more than one source. In such a case, prefix (if specified via useNameAsPrefix ) will be the names of all secrets found for those particular labels.

One more thing to bear in mind is that we support prefix per source , not per secret. The easiest way to explain this is via an example:

Suppose that a query matching such a label will provide two secrets as a result: secret-a and secret-b . Both of these secrets have the same property name: color=sea-blue and color=ocean-blue . It is undefined which color will end-up as part of property sources, but the prefix for it will be secret-a.secret-b (concatenated sorted naturally, names of the secrets).

If you need more fine-grained results, adding more labels to identify the secret uniquely would be an option.

By default, besides reading the config map that is specified in the sources configuration, Spring will also try to read all properties from "profile aware" sources. The easiest way to explain this is via an example. Let’s suppose your application enables a profile called "dev" and you have a configuration like the one below:

Besides reading the config-map-one , Spring will also try to read config-map-one-dev ; in this particular order. Each active profile generates such a profile aware config map.

Though your application should not be impacted by such a config map, it can be disabled if needed:

Notice that just like before, there are two levels where you can specify this property: for all config maps or for individual ones; the latter having a higher priority.

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.

In some cases, your application may be unable to load some of your ConfigMaps using the Kubernetes API. If you want your application to fail the start-up process in such cases, you can set spring.cloud.kubernetes.config.fail-fast=true to make the application start-up fail with an Exception.

You can also make your application retry loading ConfigMap property sources on a failure. First, you need to set spring.cloud.kubernetes.config.fail-fast=true . Then you need to add spring-retry and spring-boot-starter-aop to your classpath. You can configure retry properties such as the maximum number of attempts, backoff options like initial interval, multiplier, max interval by setting the spring.cloud.kubernetes.config.retry.* properties.

Boolean

false

Enable or disable failing the application start-up when an error occurred while loading a ConfigMap

spring.cloud.kubernetes.config.retry.enabled

Boolean

Enable or disable config retry.

spring.cloud.kubernetes.config.retry.initial-interval

Initial retry interval in milliseconds.

spring.cloud.kubernetes.config.retry.max-attempts

Integer

Maximum number of attempts.

spring.cloud.kubernetes.config.retry.max-interval

Maximum interval for backoff.

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 Fabric8SecretsPropertySource looks up Kubernetes for Secrets from the following sources:

By default, consuming Secrets through the API (points 2 and 3 above) is not enabled for security reasons. The permission 'list' on secrets allows clients to inspect secrets values in the specified namespace. 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. For more information about risks and best practices when consuming Secrets through the API refer to this doc .

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:

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:

As the case with ConfigMap , more advanced configuration is also possible where you can use multiple Secret instances. The spring.cloud.kubernetes.secrets.sources list makes this possible. For example, you could define the following Secret instances:

In the preceding example, if spring.cloud.kubernetes.secrets.namespace had not been set, the Secret named s1 would be looked up in the namespace that the application runs. See namespace-resolution to get a better understanding of how the namespace of the application is resolved.

Similar to the ConfigMaps ; if you want your application to fail to start when it is unable to load Secrets property sources, you can set spring.cloud.kubernetes.secrets.fail-fast=true .

It is also possible to enable retry for Secret property sources like the ConfigMaps . As with the ConfigMap property sources, first you need to set spring.cloud.kubernetes.secrets.fail-fast=true . Then you need to add spring-retry and spring-boot-starter-aop to your classpath. Retry behavior of the Secret property sources can be configured by setting the spring.cloud.kubernetes.secrets.retry.* properties.

Boolean

false

Enable or disable failing the application start-up when an error occurred while loading a Secret

spring.cloud.kubernetes.secrets.retry.enabled

Boolean

Enable or disable secrets retry.

spring.cloud.kubernetes.secrets.retry.initial-interval

Initial retry interval in milliseconds.

spring.cloud.kubernetes.secrets.retry.max-attempts

Integer

Maximum number of attempts.

spring.cloud.kubernetes.secrets.retry.max-interval

Maximum interval for backoff.

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

5.3. Namespace resolution

Finding an application namespace happens on a best-effort basis. There are some steps that we iterate in order to find it. The easiest and most common one, is to specify it in the proper configuration, for example:

from a String residing in a file denoted by spring.cloud.kubernetes.client.serviceAccountNamespacePath property

from a String residing in /var/run/secrets/kubernetes.io/serviceaccount/namespace file (kubernetes default namespace path)

from a designated client method call (for example fabric8’s : KubernetesClient::getNamespace ), if the client provides such a method. This, in turn, could be configured via environment properties. For example fabric8 client can be configured via "KUBERNETES_NAMESPACE" property; consult the client documentation for exact details.

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). Please notice that this will enable monitoring of configmaps only (i.e.: spring.cloud.kubernetes.reload.monitoring-config-maps will be set to true ). If you want to enable monitoring of secrets, this must be done explicitly via : spring.cloud.kubernetes.reload.monitoring-secrets=true .

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. In order for the restart context functionality to work properly you must enable and expose the restart actuator endpoint

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.

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: Periodically 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.

5.6. Reload namespace and label filtering

By default, a namespace chosen using the steps outlined in Namespace resolution will be used to listen to changes in configmaps and secrets. i.e.: if you do not tell reload what namespaces and configmaps/secrets to watch for, it will watch all configmaps/secrets from the namespace that will be computed using the above algorithm.

On the other hand, you can define a more fine-grained approach. For example, you can specify the namespaces where changes will be monitored:

Such a configuration will make the app watch changes only in the my-namespace namespace. Mind that this will watch all configmaps/secrets (depending on which one you enable). If you want an even more fine-grained approach, you can enable "label-filtering". First we need to enable such support via : enable-reload-filtering: true

What this will do, is watch configmaps/secrets that only have the spring.cloud.kubernetes.config.informer.enabled: true label.

refresh

The strategy to use when firing a reload ( refresh , restart_context , or shutdown )

spring.cloud.kubernetes.reload.mode

event

Specifies how to listen for changes in property sources ( event or polling )

spring.cloud.kubernetes.reload.period

Duration

The period for verifying changes when using the polling strategy

spring.cloud.kubernetes.reload.namespaces

String[]

namespaces where we should watch for changes

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.

All features described earlier in this guide work equally well, regardless of whether your application is running inside Kubernetes. This is really helpful for development and troubleshooting. From a development point of view, this lets you start your Spring Boot application and debug one of the modules that is part of this project. You need not deploy it in Kubernetes, as the code of the project relies on the Fabric8 Kubernetes Java client , which is a fluent DSL that can communicate by using http protocol to the REST API of the Kubernetes Server.

Kubernetes awareness is based on Spring Boot API, specifically on ConditionalOnCloudPlatform . That property will auto-detect if your application is currently deployed in kubernetes or not. It is possible to override that setting via spring.main.cloud-platform .

For example, if you need to test some features, but do not want to deploy to a cluster, it is enough to set the: spring.main.cloud-platform=KUBERNETES . This will make spring-cloud-kubernetes act as-if it is deployed in a real cluster.

6.1. Breaking Changes In 3.0.x

In versions of Spring Cloud Kubernetes prior to 3.0.x , Kubernetes awareness was implemented using spring.cloud.kubernetes.enabled property. This property was removed and is un-supported. Instead, we use Spring Boot API: ConditionalOnCloudPlatform . If it is needed to explicitly enable or disable this awareness, use spring.main.cloud-platform=NONE/KUBERNETES .

6.2. Kubernetes Profile Autoconfiguration

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).

6.3. Istio Awareness

When you include the spring-cloud-kubernetes-fabric8-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.

Spring Boot uses HealthIndicator to expose info about the health of an application. That makes it really useful for exposing health-related information to the user and makes it a good fit for use as readiness probes .

The Kubernetes health indicator (which is part of the core module) exposes the following info:

Spring Cloud Kubernetes includes an InfoContributor which adds Pod information to Spring Boot’s /info Acturator endpoint.

You can disable this InfoContributor by setting management.info.kubernetes.enabled to false in application.[properties | yaml] .

The Spring Cloud Kubernetes leader election mechanism implements the leader election API of Spring Integration using a Kubernetes ConfigMap.

Multiple application instances compete for leadership, but leadership will only be granted to one. When granted leadership, a leader application receives an OnGrantedEvent application event with leadership Context . Applications periodically attempt to gain leadership, with leadership granted to the first caller. A leader will remain a leader until either it is removed from the cluster, or it yields its leadership. When leadership removal occurs, the previous leader receives OnRevokedEvent application event. After removal, any instances in the cluster may become the new leader, including the old leader.

To include it in your project, add the following dependency.

<dependency>
    <groupId>org.springframework.cloud</groupId>
    <artifactId>spring-cloud-kubernetes-fabric8-leader</artifactId>
</dependency>

This project includes Spring Cloud Load Balancer for load balancing based on Kubernetes Endpoints and provides implementation of load balancer based on Kubernetes Service. To include it to your project add the following dependency.

<dependency>
    <groupId>org.springframework.cloud</groupId>
    <artifactId>spring-cloud-starter-kubernetes-fabric8-loadbalancer</artifactId>
</dependency>

<dependency>
    <groupId>org.springframework.cloud</groupId>
    <artifactId>spring-cloud-starter-kubernetes-client-loadbalancer</artifactId>
</dependency>

11.1. Namespace

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:

11.2. Service Account

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.

Depending on the requirements, you’ll need get , list and watch permission on the following resources:

For development purposes, you can add cluster-reader permissions to your default service account. On a production system you’ll likely want to provide more granular permissions.

The following Role and RoleBinding are an example for namespaced permissions for the default account:

In Kubernetes service registration is controlled by the platform, the application itself does not control registration as it may do in other platforms. For this reason using spring.cloud.service-registry.auto-registration.enabled or setting @EnableDiscoveryClient(autoRegister=false) will have no effect in Spring Cloud Kubernetes.

Kubernetes provides the ability to mount a ConfigMap or Secret as a volume in the container of your application. When the contents of the ConfigMap or Secret changes, the mounted volume will be updated with those changes .

However, Spring Boot will not automatically update those changes unless you restart the application. Spring Cloud provides the ability refresh the application context without restarting the application by either hitting the actuator endpoint /refresh or via publishing a RefreshRemoteApplicationEvent using Spring Cloud Bus.

To achieve this configuration refresh of a Spring Cloud app running on Kubernetes, you can deploy the Spring Cloud Kubernetes Configuration Watcher controller into your Kubernetes cluster.

The application is published as a container and is available on Docker Hub . However, if you need to customize the config watcher behavior or prefer to build the image yourself you can easily build your own image from the source code on GitHub and use that.

Spring Cloud Kubernetes Configuration Watcher can send refresh notifications to applications in two ways.

Over HTTP in which case the application being notified must of the /refresh actuator endpoint exposed and accessible from within the cluster

Using Spring Cloud Bus, in which case you will need a message broker deployed to your custer for the application to use.

The Service Account and associated Role Binding is important for Spring Cloud Kubernetes Configuration to work properly. The controller needs access to read data about ConfigMaps, Pods, Services, Endpoints and Secrets in the Kubernetes cluster.

13.2. Monitoring ConfigMaps and Secrets

Spring Cloud Kubernetes Configuration Watcher will react to changes in ConfigMaps with a label of spring.cloud.kubernetes.config with the value true or any Secret with a label of spring.cloud.kubernetes.secret with the value true . If the ConfigMap or Secret does not have either of those labels or the values of those labels is not true then any changes will be ignored.

If a change is made to a ConfigMap or Secret with valid labels then Spring Cloud Kubernetes Configuration Watcher will take the name of the ConfigMap or Secret and send a notification to the application with that name. This might not be enough for your use-case though, you could for example what to:

bind a config-map to multiple applications, so that a change inside a single configmap triggers a refresh for many services

have profile based sources trigger events for your application

spring.cloud.kubernetes.configmap.apps or spring.cloud.kubernetes.secret.apps . It takes a String of apps separated by comma, that specifies the names of applications that will receive a notification when changes happen in this secret/configmap.

For example:

13.3. HTTP Implementation

The HTTP implementation is what is used by default. When this implementation is used Spring Cloud Kubernetes Configuration Watcher and a change to a ConfigMap or Secret occurs then the HTTP implementation will use the Spring Cloud Kubernetes Discovery Client to fetch all instances of the application which match the name of the ConfigMap or Secret and send an HTTP POST request to the application’s actuator /refresh endpoint. By default it will send the post request to /actuator/refresh using the port registered in the discovery client.

13.3.1. Non-Default Management Port and Actuator Path

If the application is using a non-default actuator path and/or using a different port for the management endpoints, the Kubernetes service for the application can add an annotation called boot.spring.io/actuator and set its value to the path and port used by the application. For example

Another way you can choose to configure the actuator path and/or management port is by setting spring.cloud.kubernetes.configuration.watcher.actuatorPath and spring.cloud.kubernetes.configuration.watcher.actuatorPort .

13.4. Messaging Implementation

The messaging implementation can be enabled by setting profile to either bus-amqp (RabbitMQ) or bus-kafka (Kafka) when the Spring Cloud Kubernetes Configuration Watcher application is deployed to Kubernetes.

13.5. Configuring RabbitMQ

When the bus-amqp profile is enabled you will need to configure Spring RabbitMQ to point it to the location of the RabbitMQ instance you would like to use as well as any credentials necessary to authenticate. This can be done by setting the standard Spring RabbitMQ properties, for example

13.6. Configuring Kafka

When the bus-kafka profile is enabled you will need to configure Spring Kafka to point it to the location of the Kafka Broker instance you would like to use. This can be done by setting the standard Spring Kafka properties, for example

The Spring Cloud Kubernetes Config Server, is based on Spring Cloud Config Server and adds an environment repository for Kubernetes Config Maps and Secrets .

This is component is completely optional. However, it allows you to continue to leverage configuration you may have stored in existing environment repositories (Git, SVN, Vault, etc) with applications that you are running on Kubernetes.

A default image is located on Docker Hub which will allow you to easily get a Config Server deployed on Kubernetes without building the code and image yourself. However, if you need to customize the config server behavior or prefer to build the image yourself you can easily build your own image from the source code on GitHub and use that.

14.1. Configuration

14.1.1. Enabling The Kubernetes Environment Repository

To enable the Kubernetes environment repository the kubernetes profile must be included in the list of active profiles. You may activate other profiles as well to use other environment repository implementations.

14.1.2. Config Map and Secret PropertySources

By default, only Config Map data will be fetched. To enable Secrets as well you will need to set spring.cloud.kubernetes.secrets.enableApi=true . You can disable the Config Map PropertySource by setting spring.cloud.kubernetes.config.enableApi=false .

14.1.3. Fetching Config Map and Secret Data From Additional Namespaces

By default, the Kubernetes environment repository will only fetch Config Map and Secrets from the namespace in which it is deployed. If you want to include data from other namespaces you can set spring.cloud.kubernetes.configserver.config-map-namespaces and/or spring.cloud.kubernetes.configserver.secrets-namespaces to a comma separated list of namespace values.

14.1.4. Kubernetes Access Controls

The Kubernetes Config Server uses the Kubernetes API server to fetch Config Map and Secret data. In order for it to do that it needs ability to get and list Config Map and Secrets (depending on what you enable/disable).

The Spring Cloud Kubernetes Discovery Server provides HTTP endpoints apps can use to gather information about services available within a Kubernetes cluster. The Spring Cloud Kubernetes Discovery Server can be used by apps using the spring-cloud-starter-kubernetes-discoveryclient to provide data to the DiscoveryClient implementation provided by that starter.

15.1. Permissions

The Spring Cloud Discovery server uses the Kubernetes API server to get data about Service and Endpoint resrouces so it needs list, watch, and get permissions to use those endpoints. See the below sample Kubernetes deployment YAML for an examlpe of how to configure the Service Account on Kubernetes.

15.2. Endpoints

There are three endpoints exposed by the server.

15.2.1. /apps

A GET request sent to /apps will return a JSON array of available services. Each item contains the name of the Kubernetes service and service instance information. Below is a sample response.

15.2.2. /apps/{name}

A GET request to /apps/{name} can be used to get instance data for all instances of a given service. Below is a sample response when a GET request is made to /apps/kubernetes .

15.2.3. /app/{name}/{instanceid}

A GET request made to /app/{name}/{instanceid} will return the instance data for a specific instance of a given service. Below is a sample response when a GET request is made to /app/kubernetes/1234 .

15.3. Deployment YAML

An image of the Spring Cloud Discovery Server is hosted on Docker Hub . However, if you need to customize the discovery server behavior or prefer to build the image yourself you can easily build your own image from the source code on GitHub and use that.

Below is a sample deployment YAML you can use to deploy the Kubernetes Configuration Watcher to Kubernetes.

Spring Cloud Kubernetes tries to make it transparent for your applications to consume Kubernetes Native Services by following the Spring Cloud interfaces.

In your applications, you need to add the spring-cloud-kubernetes-discovery dependency to your classpath and remove any other dependency that contains a DiscoveryClient implementation (that is, a Eureka discovery client). The same applies for PropertySourceLocator , where you need to add to the classpath the spring-cloud-kubernetes-config and remove any other dependency that contains a PropertySourceLocator implementation (that is, a configuration server client).

The following projects highlight the usage of these dependencies and demonstrate how you can use these libraries from any Spring Boot application:

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

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-1685024835053-0/spring-cloud-kubernetes/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.

19.3. 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.

19.3.1. 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.

19.3.2. 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".

19.3.3. 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.

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.

20.1. 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.

20.2. 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] .

20.3. 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

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).

20.4. 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)

<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>

<?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

└── 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)

<build>
    <plugins>
        <plugin>
            <groupId>org.basepom.maven</groupId>
            <artifactId>duplicate-finder-maven-plugin</artifactId>
        </plugin>
    </plugins>
</build>

<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>