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Spring Cloud Consul Client

Registration with Consul

A Spring Boot service can register with a Consul Agent by making the following changes to bootstrap.yml,

spring:
  cloud:
    consul:
      host: localhost
      port: 8500

The above changes can be made in the application.yml if your service doesn't use Spring Cloud configuration functionalities of Consul.

Health Check

A Consul Agent check the health of a Spring Boot application by using the /health endpoint.

If the service uses a non-default context path, the changes to the health endpoint needs to be configured in application.yml . For example if the context path is changed to foo, the following changes need to be made:

spring:
  cloud:
    consul:
      discovery:
        healthCheckPath: foo/health
        healthCheckInterval: 15s

The interval used by Consul to check the health endpoint can also be configured.

The latest version of Consul (1.0.2) shows a registered Spring Boot application to be in critical condition.

If you check the /health endpoint of your application, the consul health will show up as down:

{
    "consul": {
        "status": "DOWN",
        "services": {
            "consul": [
        
            ],
            "spring-consul-example": [
        
            ]
        },
        "error": "java.lang.IllegalArgumentException: Value must not be null"
    }
}

This problem can be mitigated by adding the following snippet in bootstrap.yml,

management:
  security:
    enabled: false
  health:
    consul:
      enabled: false

Once you make the above changes, the service shows up as passing.

Configuration with Consul

A Spring Boot service can take advantage of Consul's KV store for storing its configuration properties. The Configurations in Consul KV store are usually stored under /config folder (data folder and not filse system folder).

For example, the properties of an application named spring-consul-example will be stored under folder,

config/spring-consul-example/

The properties of application named spring-consul-example and with dev profile will be stored under folder,

config/spring-consul-example,dev/

Proerties in config/application is applicable to all applications.

The following changes need to be made to the bootstrap.yml to enable Consul configuration,

spring:
  cloud:
    consul:
      config:
        enabled: true
        prefix: config
        profileSeparator: '::'
  • Setting enabled to true enables Consul Config
  • prefix sets the base folder for configuration values which in this example is config
  • profileSeparator sets the value of the separator used to separate the profile name in property sources with profiles

YAML Configuration

The configuration properties can be stored as a YAML blob with an appropriate data key in Consul KV store. For example the properties for the application spring-consul-example can be stored as JSON blob with data as the data key,

config/spring-consul-example/data

The YAML blob can look something as shown below,

cassandra:
  host: 127.0.0.1:9042,127.0.0.2:9042
  user: my_user
  password: my_pass

If the data is stored as a YAML blob, following properties need to be set in the bootstrap.yml,

  1. spring.cloud.consul.config.format to YAML
  2. spring.cloud.consul.config.data-key to data
spring:
  cloud:
    consul:
      config:
        format: YAML
        data-key: data

The properties can be inserted either manually from the Consul UI or via command line.

Entry of Properties from Consul Web UI

To set configuration properties from Consul UI:

  • Open the Consul UI page by opening the link, http://localhost:8500/ui/, in your favorite browser.
  • Once the page is open, navigate to KV page by clicking the KEY/VALUE button.
  • In the KV page, create a new key by entering config/spring-consul-example/data as the name of the key in text box below Create Key.
  • Enter a YAML blob or plain string in the text area below and click the CREATE button. This will enter a new set of properties

Entry of Properties from Commandline

Consul Agent also provides a command line too to create configuration properties.

  • Open a terminal and naviagte to the the directory where the Consul Agent is located.
  • To create a new property named foo with a value `bar, you can execute the following command:
$ ./consul kv put foo bar

It will create the new property,

Success! Data written to: foo
  • Once the property is created, you can also access the property from the command line,
$ ./consul kv get foo
bar

The previously created property from the UI can also be accessed by the following command:

$ ./consul kv get config/spring-consul-example/data
cassandra:
  host: 127.0.0.1:9042,127.0.0.2:9042
  user: my_user
  password: my_pass

You can also load YAMl properties from command line. The YAML data can be read from a file by prefixing the file name with the @ symbol.

$  ./consul kv put config/application/data @data.yml
Success! Data written to: config/application/data

The data can be retrieved the same way,

$ ./consul kv get config/application/data
cassandra:
  host: 127.0.0.1:9042,127.0.0.2:9042
  user: my_user
  password: my_pass

Read Configuration Properties

The configuration is loaded by Spring service during the bootstrap phase. The properties can be read from Consul KV store with the help of @Value annotation and the stored property name. Here is an example,

@Configuration
@RefreshScope
public class ConsulConfiguration {

    @Value("${cassandra.host}")
    private String cassandraHost;

    @Value("${cassandra.user}")
    private String userName;

    @Value("${cassandra.password}")
    private String password;


    /**
     * To validate that the properties are set correctly.
     */
    @PostConstruct
    public void postConstruct() {
        System.out.println("** cassandra.host: " + cassandraHost);
        System.out.println("** cassandra.user: " + userName);
        System.out.println("** cassandra.password: " + password);
    }
}

Changes to Spring Boot Application class,

@SpringBootApplication
@EnableAutoConfiguration
@EnableConfigurationProperties
@EnableDiscoveryClient
@ComponentScan(basePackages = {"com.basaki"})
public class Application {

    public static void main(String[] args) {
        SpringApplication.run(Application.class, args);
    }
}

Run

Bfore running the Spring Boot application, please make sure that the Consul Agent is up and running with the application configuration properties loaded. The Spring Boot client application can be run from the command line by the following command,

java -jar target/spring-security-consul-client-1.0.0.jar