Externalized Configuration

Sometimes it is useful that configuration in a blueprint, or in Brooklyn itself, is not given explicitly, but is instead replaced with a reference to some other storage system. For example, it is undesirable for a blueprint to contain a plain-text password for a production system, especially if (as we often recommend) the blueprints are kept in the developer's source code control system.

To handle this problem, Apache Brooklyn supports externalized configuration. This allows a blueprint to refer to a piece of information that is stored elsewhere. brooklyn.cfg defines the external suppliers of configuration information. At runtime, when Brooklyn finds a reference to externalized configuration in a blueprint, it consults brooklyn.cfg for information about the supplier, and then requests that the supplier return the information required by the blueprint.

Take, as a simple example, a web app which connects to a database. In development, the developer is running a local instance of PostgreSQL with a simple username and password. But in production, an enterprise-grade cluster of PostgreSQL is used, and a dedicated service is used to provide passwords. The same blueprint can be used to service both groups of users, with brooklyn.cfg changing the behaviour depending on the deployment environment.

Here is the blueprint:

name: MyApplication
- type: brooklyn.entity.webapp.jboss.JBoss7Server
  name: AppServer HelloWorld
    wars.root: https://search.maven.org/remotecontent?filepath=org/apache/brooklyn/example/brooklyn-example-hello-world-sql-webapp/0.12.0/brooklyn-example-hello-world-sql-webapp-0.12.0.war # BROOKLYN_VERSION
    http.port: 8080+
          - "jdbc:postgresql://%s/myappdb?user=%s&password=%s"
          - $brooklyn:external("servers", "postgresql")
          - $brooklyn:external("credentials", "postgresql-user")
          - $brooklyn:external("credentials", "postgresql-password")

You can see that when we are building up the JDBC URL, we are using the external function. This takes two parameters: the first is the name of the configuration supplier, the second is the name of a key that is stored by the configuration supplier. In this case we are using two different suppliers: servers to store the location of the server, and credentials which is a security-optimized supplier of secrets.

Developers would add lines like this to the brooklyn.cfg file on their workstation:


In this case, all of the required information is included in-line in the local brooklyn.cfg.

Whereas in production, brooklyn.cfg might look like this:


In this case, the list of servers is stored in a properties file located on an Operations Department web server, and the credentials are stored in an instance of Vault. More information on these providers is below.

For demo purposes, there is a pre-defined external provider called brooklyn-demo-sample which defines hidden-brooklyn-password as br00k11n. This is used in some of the sample blueprints, referencing $brooklyn:external("brooklyn-demo-sample", "hidden-brooklyn-password"). The value used here can be overridden with the following in your brooklyn.cfg:


Defining Suppliers

External configuration suppliers are defined in brooklyn.cfg. The minimal definition is of the form:

brooklyn.external.supplierName = className

This defines a supplier named supplierName. Brooklyn will attempt to instantiate className; it is this class which will provide the behaviour of how to retrieve data from the supplier. Brooklyn includes a number of supplier implementations; see below for more details.

Suppliers may require additional configuration options. These are given as additional properties in brooklyn.cfg:

brooklyn.external.supplierName = className
brooklyn.external.supplierName.firstConfig = value
brooklyn.external.supplierName.secondConfig = value

Referring to External Configuration in Blueprints

Externalized configuration adds a new function to the Brooklyn blueprint language DSL, $brooklyn:external. This function takes two parameters:

  1. supplier
  2. key

When resolving the external reference, Brooklyn will first identify the supplier of the information, then it will give the supplier the key. The returned value will be substituted into the blueprint.

You can use $brooklyn:external directly:

name: MyApplication
  example: $brooklyn:external("supplier", "key")

or embed the external function inside another $brooklyn DSL function, such as $brooklyn:formatString:

name: MyApplication
  example: $brooklyn:formatString("%s", external("supplier", "key"))

Referring to External Configuration in brooklyn.cfg

The same blueprint language DSL can be used from brooklyn.cfg. For example:

brooklyn.location.jclouds.aws-ec2.identity=$brooklyn:external("mysupplier", "aws-identity")
brooklyn.location.jclouds.aws-ec2.credential=$brooklyn:external("mysupplier", "aws-credential")

Referring to External Configuration in Catalog Items

The same blueprint language DSL can be used within YAML catalog items. For example:

  id: com.example.myblueprint
  version: "1.2.3"
  itemType: entity
  - >
    external("mysupplier", "username"), external("mysupplier", "password"))
    type: com.example.MyBlueprint

Note the > in the example above is used to split across multiple lines.

Suppliers available with Brooklyn

Brooklyn ships with a number of external configuration suppliers ready to use.


InPlaceExternalConfigSupplier embeds the configuration keys and values as properties inside brooklyn.cfg. For example:


Then, a blueprint which referred to $brooklyn:external("servers", "postgresql") would receive the value

Properties file

PropertiesFileExternalConfigSupplier loads a properties file from a URL, and uses the keys and values in this file to respond to configuration lookups.

Given this configuration:


This would cause the supplier to download the given URL. Assuming that the file contained this entry:


Then, a blueprint which referred to $brooklyn:external("servers", "postgresql") would receive the value


Vault is a server-based tool for managing secrets. Brooklyn provides suppliers that are able to query the Vault REST API for configuration values. The different suppliers implement alternative authentication options that Vault provides.

For all of the authentication methods, you must always set these properties in brooklyn.cfg:

brooklyn.external.supplierName.endpoint=<Vault HTTP/HTTPs endpoint>
brooklyn.external.supplierName.path=<path to a Vault object>

For example, if the path is set to secret/brooklyn, then attempting to retrieve the key foo would cause Brooklyn to retrieve the value of the foo key on the secret/brooklyn object. This value can be set using the Vault CLI like this:

vault write secret/brooklyn foo=bar

Authentication by username and password

The userpass plugin for Vault allows authentication with username and password.


Authentication using App ID

The app_id plugin for Vault allows you to specify an "app ID", and then designate particular "user IDs" to be part of the app. Typically the app ID would be known and shared, but user ID would be autogenerated on the client in some way. Brooklyn implements this by determining the MAC address of the server running Brooklyn (expressed as 12 lower case hexadecimal digits without separators) and passing this as the user ID.


If you do not wish to use the MAC address as the user ID, you can override it with your own choice of user ID:


Authentication by fixed token

If you have a fixed token string, then you can use the VaultTokenExternalConfigSupplier class and provide the token in brooklyn.cfg:


This supplier is suitable for "smoke testing" the Vault supplier using the Initial Root Token or similar. However it is not suitable for production use as it is inherently insecure - should the token be compromised, an attacker could have complete access to your Vault, and the cleanup operation would be difficult. Instead you should use one of the other suppliers.

Writing Custom External Configuration Suppliers

Supplier implementations must conform to the brooklyn.config.external.ExternalConfigSupplier interface, which is very simple:

String getName();
String get(String key);

Classes implementing this interface can be placed in the lib/dropins folder of Brooklyn, and then the supplier defined in brooklyn.cfg as normal.

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