Configuration Server - Spring Cloud

CAS is able to use an external and central configuration server to obtain state and settings. The configuration server provides a very abstract way for CAS (and all of its other clients) to obtain settings from a variety of sources, such as file system, git or svn repositories, MongoDb databases, Vault, etc. The beauty of this solution is that to the CAS web application server, it matters not where settings come from and it has no knowledge of the underlying property sources. It talks to the configuration server to locate settings and move on.

Configuration Security

This is a very good strategy to ensure configuration settings are not scattered around various deployment environments leading to a more secure deployment. The configuration server need not be exposed to the outside world, and it can safely and secure be hidden behind firewalls, etc allowing access to only authorized clients such as the CAS server web application.

A full comprehensive guide is provided by the Spring Cloud project.

Spring Cloud Configuration Server Overlay

The configuration server itself, similar to CAS, can be deployed using the CAS Initializr.

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<dependency>
  <groupId>org.apereo.cas</groupId>
  <artifactId>cas-server-webapp-config-server</artifactId>
  <version>${cas.version}</version>
</dependency>

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implementation "org.apereo.cas:cas-server-webapp-config-server:${project.'cas.version'}"

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dependencyManagement {
  imports {
    mavenBom "org.apereo.cas:cas-server-support-bom:${project.'cas.version'}"
  }
}

dependencies {  
  implementation "org.apereo.cas:cas-server-webapp-config-server"
}

In addition to the strategies outlined here, the configuration server may load CAS settings and properties via the following order and mechanics:

  1. Profile-specific application properties outside of your packaged web application (application-{profile}.properties|yml)
  2. Profile-specific application properties packaged inside your jar (application-{profile}.properties|yml)
  3. Application properties outside of your packaged jar (application.properties|yml).
  4. Application properties packaged inside your jar (application.properties|yml).

The configuration and behavior of the configuration server is also controlled by its own src/main/resources/bootstrap.properties file. By default, it runs under port 8888 at /casconfigserver inside an embedded Apache Tomcat server whose endpoints are protected with basic authentication where the default credentials are casuser and an auto-generated password defined in src/main/resources/application.properties.

Furthermore, by default it runs under a native profile described below.

The following endpoints are secured and exposed by the configuration server:

Parameter Description
/encrypt Accepts a POST to encrypt CAS configuration settings.
/decrypt Accepts a POST to decrypt CAS configuration settings.
/actuator/refresh Accepts a POST and attempts to refresh the internal state of configuration server.
/actuator/env Accepts a GET and describes all configuration sources of the configuration server.
/actuator/cas/default Describes what the configuration server knows about the default settings profile.
/actuator/cas/native Describes what the configuration server knows about the native settings profile.

Once you have the configuration server deployed and assuming the credentials used to secure the configuration server match the example below, you can observe the collection of settings via:

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curl -u casuser:Mellon https://config.server.url:8888/casconfigserver/cas/native

Assuming actuator endpoints are enabled in the configuration, you can also observe the collection of property sources that provide settings to the configuration server:

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curl -u casuser:Mellon https://config.server.url:8888/casconfigserver/actuator/env
Actuator Endpoints

Remember that actuator endpoints typically are prefixed with /actuator.

Spring Cloud Configuration Server Clients

To let the CAS server web application (or any other client for that matter) talk to the configuration server, the following settings need to be applied to CAS’ own src/main/resources/bootstrap.properties file. The properties to configure the CAS server web application as the client of the configuration server must necessarily be read in before the rest of the application’s configuration is read from the configuration server, during the bootstrap phase.

The following settings and properties are available from the CAS configuration catalog:

The configuration settings listed below are tagged as Required in the CAS configuration metadata. This flag indicates that the presence of the setting may be needed to activate or affect the behavior of the CAS feature and generally should be reviewed, possibly owned and adjusted. If the setting is assigned a default value, you do not need to strictly put the setting in your copy of the configuration, but should review it nonetheless to make sure it matches your deployment expectations.

The configuration settings listed below are tagged as Optional in the CAS configuration metadata. This flag indicates that the presence of the setting is not immediately necessary in the end-user CAS configuration, because a default value is assigned or the activation of the feature is not conditionally controlled by the setting value. You should only include this field in your configuration if you need to modify the default value.

The configuration settings listed below are tagged as Third Party in the CAS configuration metadata. This flag indicates that the configuration setting is not controlled, owned or managed by the CAS ecosystem, and affects functionality that is offered by a third-party library, such as Spring Boot or Spring Cloud to CAS. For additional info, you might have to visit the third-party source to find more details.

Configuration Metadata

The collection of configuration properties listed in this section are automatically generated from the CAS source and components that contain the actual field definitions, types, descriptions, modules, etc. This metadata may not always be 100% accurate, or could be lacking details and sufficient explanations.

Be Selective

This section is meant as a guide only. Do NOT copy/paste the entire collection of settings into your CAS configuration; rather pick only the properties that you need. Do NOT enable settings unless you are certain of their purpose and do NOT copy settings into your configuration only to keep them as reference. All these ideas lead to upgrade headaches, maintenance nightmares and premature aging.

YAGNI

Note that for nearly ALL use cases, declaring and configuring properties listed here is sufficient. You should NOT have to explicitly massage a CAS XML/Java/etc configuration file to design an authentication handler, create attribute release policies, etc. CAS at runtime will auto-configure all required changes for you. If you are unsure about the meaning of a given CAS setting, do NOT turn it on without hesitation. Review the codebase or better yet, ask questions to clarify the intended behavior.

Naming Convention

Property names can be specified in very relaxed terms. For instance cas.someProperty, cas.some-property, cas.some_property are all valid names. While all forms are accepted by CAS, there are certain components (in CAS and other frameworks used) whose activation at runtime is conditional on a property value, where this property is required to have been specified in CAS configuration using kebab case. This is both true for properties that are owned by CAS as well as those that might be presented to the system via an external library or framework such as Spring Boot, etc.

When possible, properties should be stored in lower-case kebab format, such as cas.property-name=value. The only possible exception to this rule is when naming actuator endpoints; The name of the actuator endpoints (i.e. ssoSessions) MUST remain in camelCase mode.

Settings and properties that are controlled by the CAS platform directly always begin with the prefix cas. All other settings are controlled and provided to CAS via other underlying frameworks and may have their own schemas and syntax. BE CAREFUL with the distinction. Unrecognized properties are rejected by CAS and/or frameworks upon which CAS depends. This means if you somehow misspell a property definition or fail to adhere to the dot-notation syntax and such, your setting is entirely refused by CAS and likely the feature it controls will never be activated in the way you intend.

Validation

Configuration properties are automatically validated on CAS startup to report issues with configuration binding, specially if defined CAS settings cannot be recognized or validated by the configuration schema. The validation process is on by default and can be skipped on startup using a special system property SKIP_CONFIG_VALIDATION that should be set to true. Additional validation processes are also handled via Configuration Metadata and property migrations applied automatically on startup by Spring Boot and family.

Indexed Settings

CAS settings able to accept multiple values are typically documented with an index, such as cas.some.setting[0]=value. The index [0] is meant to be incremented by the adopter to allow for distinct multiple configuration blocks.

Remember that configuration server serves property sources from /{name}/{profile}/{label} to applications, where the default bindings in the client app are the following:

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"name" = ${spring.application.name}
"profile" = ${spring.profiles.active}
"label" = "master"

All of them can be overridden by setting spring.cloud.config.* (where * is name, profile or label). The “label” is useful for rolling back to previous versions of configuration; with the default Config Server implementation it can be a git label, branch name or commit id. Label can also be provided as a comma-separated list, in which case the items in the list are tried on-by-one until one succeeds. This can be useful when working on a feature branch, for instance, when you might want to align the config label with your branch, but make it optional (e.g. spring.cloud.config.label=myfeature,develop).

To lean more about how CAS allows you to reload configuration changes, please review this guide.

Spring Cloud Configuration Server Sources

Various configuration profiles exist to determine how configuration server should retrieve properties and settings.

The cloud configuration modules provided above may also be used verbatim inside a CAS server overlay. Remember that the primary objective for these modules is to retrieve settings and properties from a source. While they are mostly and primarily useful when activated inside the Spring Cloud Configuration server and can be set to honor profiles and such, they nonetheless may also be used inside a CAS server overlay directly to fetch settings from a source while running in standalone mode. In such scenarios, all sources of configuration regardless of format or syntax will work alongside each other to retrieve settings and you can certainly mix and match as you see fit.

Spring Cloud Configuration Server Composite Sources

In some scenarios you may wish to pull configuration data from multiple environment repositories. To do this just enable multiple profiles in your configuration server’s application properties or YAML file. If, for example, you want to pull configuration data from a Git repository as well as a SVN repository you would set the following properties for your configuration server.

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spring:
  profiles:
    active: git, svn
  cloud:
    config:
      server:
        svn:
          uri: file:///path/to/svn/repo
          order: 2
        git:
          uri: file:///path/to/git/repo
          order: 1

In addition to each repo specifying a URI, you can also specify an order property. The order property allows you to specify the priority order for all your repositories. The lower the numerical value of the order property the higher priority it will have. The priority order of a repository will help resolve any potential conflicts between repositories that contain values for the same properties.

Spring Cloud Configuration Server Property Overrides

The configuration server has an “overrides” feature that allows the operator to provide configuration properties to all applications that cannot be accidentally changed by the application using the normal change events and hooks. To declare overrides add a map of name-value pairs to spring.cloud.config.server.overrides.

For example:

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spring:
  cloud:
    config:
      server:
        overrides:
          foo: bar

This will cause the CAS server (as the client of the configuration server) to read foo=bar independent of its own configuration.