Writing Client Applications

Refer to the “Cook” sample app to follow along with the code in this topic.

To use a Spring Boot app as a client for a Config Server instance, you must add the dependencies listed in Client Dependencies to your app’s build file. Be sure to include the dependencies for Config Server as well.

Important: Because of a dependency on Spring Security, the Spring Cloud® Config Client starter will by default cause all app endpoints to be protected by HTTP Basic authentication. If you wish to disable this, please see Disable HTTP Basic Authentication below.

Use Configuration Values

When the app requests a configuration from the Config Server, it will use a path containing the application name. You can declare the application name in the bootstrap.yml or application.yml file.

In bootstrap.yml:

spring:
  application:
    name: cook

This app will use a path with the application name cook, so the Config Server will look in its configuration source for files whose names begin with cook, and return configuration properties from those files.

Now you can (for example) inject a configuration property value using the @Value annotation. The Menu class reads the value of special from the cook.special configuration property.

@RefreshScope
@Component
public class Menu {

  @Value("${cook.special:none}")
  String special;

  //...

  public String getSpecial() {
    return special;
  }

  //...

}

The CookController class is a @RestController. It has a private menu and returns the special (the value of which will be supplied by the Config Server) in its restaurant() method, which it maps to /restaurant.

@RestController
public class CookController {

  private final Menu menu;

  public CookController(Menu menu) {
    this.menu = menu;
  }

  @RequestMapping("/restaurant")
  public String restaurant() {
    return String.format("Today's special is: %s", menu.getSpecial());
  }

  //...

Vary Configurations Based on Profiles

You can provide configurations for multiple profiles by including appropriately-named .yml or .properties files in the Config Server instance’s configuration source (the Git repository). Filenames follow the format {application}-{profile}.{extension}, as in cook-production.yml. (See Profile-Specific Configuration.)

The app will request configurations for any active profiles. To set profiles as active, you can use the SPRING_PROFILES_ACTIVE environment variable, set for example in manifest.yml.

---
applications:
  - name: cook
    host: cookie
    instances: 1
    memory: 1G
    services:
      - cook-config-server
    env:
      SPRING_PROFILES_ACTIVE: development

The sample configuration source cook-config contains the files cook.properties and cook-production.properties. If you add production to the list of active profiles, the app will make a request of the Config Server using the path /cook/production, and the Config Server will return properties from both cook-production.properties (the profile-specific configuration) and cook.properties (the default configuration); for example:

{
  "name":"cook",
  "profiles":[
    "production"
  ],
  "label":"master",
  "propertySources":[
    {
      "name":"https://github.com/spring-cloud-services-samples/cook-config/cook-production.properties",
      "source":
        {
          "cook.special":"Cake a la mode"
        }
    },
    {
      "name":"https://github.com/spring-cloud-services-samples/cook-config/cook.properties",
      "source":
        {
          "cook.special":"Pickled Cactus"
        }
    }
  ]
}

When the Config Server returns multiple values for a configuration property, the app must decide which value to use for the property. A Spring app will take the first value for each property. In the example response above, the configuration for the production profile is first in the list, so the Spring Boot sample app will use values from that configuration.

View Client Application Configuration

Spring Boot Actuator adds an env endpoint to the app and maps it to /actuator/env. This endpoint displays the app’s profiles and property sources from the Spring ConfigurableEnvironment. (See “Endpoints” in the “Spring Boot Actuator” section of the Spring Boot Reference Guide.) In the case of an app which is bound to a Config Server service instance, env will display properties provided by the instance.

To use Actuator, you must add the spring-boot-starter-actuator dependency to your project. If using Maven, add to pom.xml:

<dependency>
  <groupId>org.springframework.boot</groupId>
  <artifactId>spring-boot-starter-actuator</artifactId>
</dependency>

If using Gradle, add to build.gradle:

compile("org.springframework.boot:spring-boot-starter-actuator")

You can now visit /actuator/env to see the application environment’s properties (the following shows an excerpt of an example response):

$ curl http://cookie.apps.wise.com/actuator/env
{
  "activeProfiles": [
  "development",
  "cloud"
  ],
  "propertySources": [
    ...
    {
      "name": "configService:configClient",
      "properties": {
        "config.client.version": {
          "value": "85c636fc400632e45985bdc86651b5f6e3efae73"
        }
      }
    },
    {
      "name": "configService:https://github.com/spring-cloud-services-samples/cook-config/cook.properties",
      "properties": {
        "cook.special": {
          "value": "Pickled Cactus"
        }
      }
    },
    ...
  ]
}

Refresh Client Application Configuration

Spring Boot Actuator also adds a refresh endpoint to the app. This endpoint is mapped to /actuator/refresh, and a POST request to the refresh endpoint refreshes any beans which are annotated with @RefreshScope. You can thus use @RefreshScope to refresh properties which were initialized with values provided by the Config Server.

The Menu.java class is marked as a @Component and also annotated with @RefreshScope.

import org.springframework.cloud.context.config.annotation.RefreshScope;
import org.springframework.stereotype.Component;

@RefreshScope
@Component
public class Menu {

  @Value("${cook.special}")
  String special;
  //...

This means that after you change values in the configuration source Git repository, you can update the special on the CookController class’s menu by creating a refresh event for the app:

$ curl http://cookie.apps.wise.com/restaurant
Today's special is: Pickled Cactus

$ git commit -am "new special"
[master 3c9ff23] new special
 1 file changed, 1 insertion(+), 1 deletion(-)

$ git push

$ curl -X POST -d {} -H "Content-Type: application/json" http://cookie.apps.wise.com/actuator/refresh
["cook.special"]

$ curl http://cookie.apps.wise.com/restaurant
Today's special is: Birdfeather Tea

Use Client-Side Decryption

On the Config Server, the decryption features are disabled, so encrypted property values from a configuration source are delivered to client apps unmodified. You can use the decryption features of Spring Cloud Config Client to perform client-side decryption of encrypted values.

To use the decryption features in a client app, you must use a Java buildpack which contains the Java Cryptography Extension (JCE) Unlimited Strength policy files. These files are contained in the Cloud Foundry Java buildpack from version 3.7.1.

If you cannot use version 3.7.1 or later, you can add the JCE Unlimited Strength policy files to an earlier version of the Cloud Foundry Java buildpack. Fork the buildpack on GitHub, then download the policy files from Oracle and place them in the buildpack’s resources/open_jdk_jre/lib/security directory. Follow the instructions in Managing Custom Buildpacks to add this buildpack to Pivotal Cloud Foundry. Be sure that it has the lowest position of all enabled Java buildpacks.

You must also include Spring Security RSA as a dependency.

If using Maven, include in pom.xml:

    <dependency>
      <groupId>org.springframework.security</groupId>
      <artifactId>spring-security-rsa</artifactId>
    </dependency>

If using Gradle, include in build.gradle:

    compile("org.springframework.security:spring-security-rsa")

Encrypted values must be prefixed with the string {cipher}. If using YAML, enclose the entire value in single quotes, as in '{cipher}vALuE'; if using a properties file, do not use quotes. The configuration source for the Cook app has a secretMenu property in its cook-encryption.properties:

secretMenu={cipher}AQA90Q3GIRAMu6ToMqwS++En2iFzMXIWX99G66yaZFRHrQNq64CntqOzWymd3xE7uJpZK
Qc9XBIkfyRz/HUGhXRdf3KZQ9bqclwmR5vkiLmN9DHlAxS+6biT+7f8ptKo3fzQ0gGOBaR4kTnWLBxmVaIkjq1Qz
e4aIgsgUWuhbEek+3znkH9+Mc+5zNPvwN8hhgDMDVzgZLB+4YnvWJAq3Au4wEevakAHHxVY0mXcxj1Ro+H+ZelIz
fF8K2AvC3vmvlmxy9Y49Zjx0RhMzUx17eh3mAB8UMMRJZyUG2a2uGCXmz+UunTA5n/dWWOvR3VcZyzXPFSFkhNek
w3db9XZ7goceJSPrRN+5s+GjLCPr+KSnhLmUt1XAScMeqTieNCHT5I=

Put the key on the client app classpath. You can either add the keystore to the buildpack’s resources/open_jdk_jre/lib/security directory (as described above for the JCE policy files) or include it with the source for the app. In the Cook app, the key is placed in src/main/resources.

cook
└── src
    └── main
        └── resources
            ├── application.yml
            ├── bootstrap.yml
            └── server.jks

Important: Cook is an example app, and the key is packaged with the application source for example purposes. If at all possible, use the buildpack for keystore distribution.

Specify the key location and credentials in bootstrap.properties or bootstrap.yml using the encrypt.keyStore properties:

encrypt:
  keyStore:
    location: classpath:/server.jks
    password: letmein
    alias: mytestkey
    secret: changeme

The Menu class has a String property secretMenu.

  @Value("${secretMenu:none}")
  String secretMenu;

  //...

  public String getSecretMenu() {
    return secretMenu;
  }

In the CookController class, the method secretMenu() is mapped to /restaurant/secret-menu. It returns the value of the secretMenu property.

    @RequestMapping("/restaurant/secret-menu")
    public String secretMenu() {
      return menu.getSecretMenu();
    }

After making the key available to the app and installing the JCE policy files in the Java buildpack (if necessary), you can cause the Config Server to serve properties from the cook-encryption.properties file by activating the encryption profile on the app, for example by running cf set-env to set the SPRING_PROFILES_ACTIVE environment variable:

$ cf set-env cook SPRING_PROFILES_ACTIVE development,encryption

$ cf restage cook

The app will decrypt the encrypted property after receiving it from the Config Server. You can view the property value by visiting /restaurant/secret-menu on the app.

Use Plain Text Configuration Files

You can use the Config Server to serve the contents of a plain text file from a Git repository. The Spring Cloud Services Config Client library adds a PlainTextConfigClient that can read in a text file and make its contents available to a client app.

The PlainTextConfigClient provides a getConfigFile() method which accepts an application profile, a label, and a filename. You can use this method to retrieve a Spring Resource. The Cook app has a DessertMenu class whose fetchMenu() method takes the InputStream from the retrieved Resource and uses the copyToString() method of Spring’s StreamUtils to return a String.

  public String fetchMenu() throws IOException {
    if (configClient == null) {
      return "none";
    }
    InputStream input = configClient.getConfigFile("cloud", "master", "dessert.json").getInputStream();
    return StreamUtils.copyToString(input, Charset.defaultCharset());
  }

The CookController has a dessertMenu() method, which is mapped to /restaurant/dessert-menu and returns the String from DessertMenu.fetchMenu().

  @RequestMapping("/restaurant/dessert-menu")
  public String dessertMenu() throws IOException {
    return dessertMenu.fetchMenu();
  }

Use a HashiCorp Vault Server

You can configure the Config Server to use a HashiCorp Vault server as a configuration source, as described in Configuring with Vault. To consume configuration from the Vault server via the service instance, your client app must enable Spring’s scheduled task execution support and be given a Vault token. The Spring Cloud Services Connectors for Config Server will automatically renew the app’s token for as long as the app is running.

Important: If the app is entirely stopped (i.e., no instances continue to run) and its Vault token expires, you will need to create a new token for the app and re-set the SPRING_CLOUD_CONFIG_TOKEN environment variable.

To enable Spring scheduled task support, add the Spring @EnableScheduling annotation to a configuration class in your app:

package cook;

import org.springframework.boot.SpringApplication;
import org.springframework.boot.autoconfigure.SpringBootApplication;
import org.springframework.scheduling.annotation.EnableScheduling;

@EnableScheduling
@SpringBootApplication
public class CookApplication {

    public static void main(String[] args) {
    //...

To generate a token for use in the app, you can run the vault token-create command, providing a Time To Live (TTL) that is long enough for the app to be restaged after you have set the environment variable. The following command creates a token with a TTL of one hour:

$ vault token-create -ttl="1h"

After generating the token, set the environment variable on your client app and then restage the app for the environment variable setting to take effect:

$ cf set-env cook SPRING_CLOUD_CONFIG_TOKEN c3432ef5-6a78-8673-ea23-5528c26849e4

$ cf restage cook

The Spring Cloud Services Connectors for Config Server renew the app token for as long as the app continues to run. For more information about the token renewal performed by the connectors, see the HashiCorp Vault Token Renewal section of Spring Cloud Connectors.

Renew Vault Token Manually

After creating a Vault token for an app, you can renew the token manually using the Config Server service instance bound to the app.

Note: The following procedure uses the jq command-line JSON processing tool.

Run cf env, giving the name of an app that is bound to the service instance:

$ cf services
Getting services in org myorg / space development as user...
OK

name             service           plan        bound apps   last operation
config-server    p-config-server   standard    vault-app    create succeeded

$ cf env vault-app
Getting env variables for app vault-app in org myorg / space development as user...
OK

System-Provided:
{
 "VCAP_SERVICES": {
  "p-config-server": [
   {
    "credentials": {
     "access_token_uri": "https://p-spring-cloud-services.uaa.cf.wise.com/oauth/token",
     "client_id": "p-config-server-876cd13b-1564-4a9a-9d44-c7c8a6257b73",
     "client_secret": "rU7dMUw6bQjR",
     "uri": "https://config-86b38ce0-eed8-4c01-adb4-1a651a6178e2.apps.wise.com"
    },
[...]

Then create a Bash script that accesses the Vault token renewal endpoint on the service instance backing app:

TOKEN=$(curl -k [ACCESS_TOKEN_URI] -u [CLIENT_ID]:[CLIENT_SECRET] \
-d grant_type=client_credentials | jq -r .access_token); \
curl -H "Authorization: bearer $TOKEN" -H "X-VAULT-Token: [VAULT_TOKEN]" \
-H "Content-Type: application/json" -X POST \
[URI]/vault/v1/auth/token/renew-self -d '{"increment": [INTERVAL]}'

This script retrieves an access token using an OAuth 2.0 credential exchange with Cloud Foundry’s UAA service. After being given an authorization token, it uses this token to make a call to the service instance’s API endpoints.

Replace the following placeholders in the script with values from the cf env command above:

  • [ACCESS_TOKEN_URI] with the value of p-config-server.credentials.access_token_uri
  • [CLIENT_ID] with the value of p-config-server.credentials.client_id
  • [CLIENT_SECRET] with the value of p-config-server.credentials.client_secret
  • [URI] with the value of p-config-server.credentials.uri

Replace the following placeholders with the relevant values:

  • [VAULT_TOKEN] with the Vault token string
  • [INTERVAL] with the number of seconds to set as the Vault token’s Time To Live (TTL)

After renewing the token, you can view its TTL by looking it up using the Vault command line. Run vault token-lookup [TOKEN], replacing [TOKEN] with the Vault token string:

$ vault token-lookup 72ec7ca0-de41-b2dc-8fe4-d74c4c9a4e75
Key                  Value
---                  -----
accessor             436db91b-6bfb-9eec-7bfb-913260488ce8
creation_time        1493360487
creation_ttl         3600
display_name         token
explicit_max_ttl     0
id                   72ec7ca0-de41-b2dc-8fe4-d74c4c9a4e75
last_renewal_time    1493360718
meta                 
num_uses             0
orphan               false
path                 auth/token/create
policies             [root]
renewable            true
ttl                  997

Disable HTTP Basic Authentication

The Spring Cloud Config Client starter has a dependency on Spring Security. Unless your app has other security configuration, this will cause all app endpoints to be protected by HTTP Basic authentication.

If you do not yet want to address application security, you may turn off Basic authentication using a class that extends Spring Security’s WebSecurityConfigurerAdapter and is annotated with the Spring @Configuration annotation. The sample app disables all default security for the development profile only, using the @Profile annotation:

@Configuration
@Profile("development")
public class SecurityConfiguration extends WebSecurityConfigurerAdapter {

  @Override
  protected void configure(HttpSecurity http) throws Exception {
    http
        .authorizeRequests().anyRequest().permitAll()
        .and()
        .httpBasic().disable()
        .csrf().disable();
  }

}

For more information, see “Security” in the Spring Boot Reference Guide.

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