Spring Cloud Config provides server and client-side support for externalized configuration in a distributed system. With the Config Server you have a central place to manage external properties for applications across all environments. The concepts on both client and server map identically to the Spring Environment
and PropertySource
abstractions, so they fit very well with Spring applications, but can be used with any application running in any language. As an application moves through the deployment pipeline from dev to test and into production you can manage the configuration between those environments and be certain that applications have everything they need to run when they migrate. The default implementation of the server storage backend uses git so it easily supports labelled versions of configuration environments, as well as being accessible to a wide range of tooling for managing the content. It is easy to add alternative implementations and plug them in with Spring configuration.
Quick Start
Start the server:
$ cd spring-cloud-config-server $ mvn spring-boot:run
The server is a Spring Boot application so you can build the jar file
and run that (java -jar …
) or pull it down from a Maven
repository. Then try it out as a client:
$ curl localhost:8888/foo/development {"name":"development","label":"master","propertySources":[ {"name":"https://github.com/scratches/config-repo/foo-development.properties","source":{"bar":"spam"}}, {"name":"https://github.com/scratches/config-repo/foo.properties","source":{"foo":"bar"}} ]}
The default strategy for locating property sources is to clone a git
repository (at "spring.cloud.config.server.git.uri") and use it to
initialize a mini SpringApplication
. The mini-application’s
Environment
is used to enumerate property sources and publish them
via a JSON endpoint.
The HTTP service has resources in the form:
/{application}/{profile}[/{label}] /{application}-{profile}.yml /{label}/{application}-{profile}.yml /{application}-{profile}.properties /{label}/{application}-{profile}.properties
where the "application" is injected as the "spring.config.name" in the
SpringApplication
(i.e. what is normally "application" in a regular
Spring Boot app), "profile" is an active profile (or comma-separated
list of properties), and "label" is an optional git label (defaults to
"master".)
The YAML and properties forms are coalesced into a single map, even if the origin of the values (reflected in the "propertySources" of the "standard" form) has multiple sources.
Spring Cloud Config Server pulls configuration for remote clients from a git repository (which must be provided):
spring: cloud: config: server: git: uri: https://github.com/spring-cloud-samples/config-repo
Client Side Usage
To use these features in an application, just build it as a Spring
Boot application that depends on spring-cloud-config-client (e.g. see
the test cases for the config-client, or the sample app). The most
convenient way to add the dependency is via a Spring Boot starter
org.springframework.cloud:spring-cloud-starter-config
. There is also a
parent pom and BOM (spring-cloud-starter-parent
) for Maven users and a
Spring IO version management properties file for Gradle and Spring CLI
users. Example Maven configuration:
<parent>
<groupId>org.springframework.boot</groupId>
<artifactId>spring-boot-starter-parent</artifactId>
<version>1.2.3.RELEASE</version>
<relativePath /> <!-- lookup parent from repository -->
</parent>
<dependencyManagement>
<dependencies>
<dependency>
<groupId>org.springframework.cloud</groupId>
<artifactId>spring-cloud-starter-parent</artifactId>
<version>1.0.1.RELEASE</version>
<type>pom</type>
<scope>import</scope>
</dependency>
</dependencies>
</dependencyManagement>
<dependencies>
<dependency>
<groupId>org.springframework.cloud</groupId>
<artifactId>spring-cloud-starter-config</artifactId>
</dependency>
<dependency>
<groupId>org.springframework.boot</groupId>
<artifactId>spring-boot-starter-test</artifactId>
<scope>test</scope>
</dependency>
</dependencies>
<build>
<plugins>
<plugin>
<groupId>org.springframework.boot</groupId>
<artifactId>spring-boot-maven-plugin</artifactId>
</plugin>
</plugins>
</build>
<!-- repositories also needed for snapshots and milestones -->
Then you can create a standard Spring Boot application, like this simple HTTP server:
@Configuration @EnableAutoConfiguration @RestController public class Application { @RequestMapping("/") public String home() { return "Hello World!"; } public static void main(String[] args) { SpringApplication.run(Application.class, args); } }
When it runs it will pick up the external configuration from the
default local config server on port 8888 if it is running. To modify
the startup behaviour you can change the location of the config server
using bootstrap.properties
(like application.properties
but for
the bootstrap phase of an application context), e.g.
spring.cloud.config.uri: http://myconfigserver.com
The bootstrap properties will show up in the /env
endpoint as a
high-priority property source, e.g.
$ curl localhost:8080/env { "profiles":[], "configService:https://github.com/spring-cloud-samples/config-repo/bar.properties":{"foo":"bar"}, "servletContextInitParams":{}, "systemProperties":{...}, ... }
(a property source called "configService:<URL of remote repository>/<file name>" contains the property "foo" with value "bar" and is highest priority).
Note
|
the URL in the property source name is the git repository not the config server URL. |
Spring Cloud Config Server
The Server provides an HTTP, resource-based API for external
configuration (name-value pairs, or equivalent YAML content). The
server is easily embeddable in a Spring Boot application using the
@EnableConfigServer
annotation.
Environment Repository
Where do you want to store the configuration data for the Config
Server? The strategy that governs this behaviour is the
EnvironmentRepository
, serving Environment
objects. This
Environment
is a shallow copy of the domain from the Spring
Environment
(including propertySources
as the main feature). The
Environment
resources are parametrized by three variables:
-
{application}
maps to "spring.application.name" on the client side; -
{profile}
maps to "spring.active.profiles" on the client (comma separated list); and -
{label}
which is a server side feature labelling a "versioned" set of config files.
Repository implementations generally behave just like a Spring Boot
application loading configuration files from a "spring.config.name"
equal to the {application}
parameter, and "spring.profiles.active"
equal to the {profiles}
parameter. Precedence rules for profiles are
also the same as in a regular Boot application: active profiles take
precedence over defaults, and if there are multiple profiles the last
one wins (like adding entries to a Map
).
Example: a client application has this bootstrap configuration:
spring: application: name: foo profiles: active: dev,mysql
(as usual with a Spring Boot application, these properties could also be set as environment variables or command line arguments).
If the repository is file-based, the server will create an
Environment
from application.yml
(shared between all clients), and
foo.yml
(with foo.yml
taking precedence). If the YAML files have
documents inside them that point to Spring profiles, those are applied
with higher precendence (in order of the profiles listed), and if
there are profile-specific YAML (or properties) files these are also
applied with higher precedence than the defaults. Higher precendence
translates to a PropertySource
listed earlier in the
Environment
. (These are the same rules as apply in a standalone
Spring Boot application.)
Git Backend
The default implementation of EnvironmentRepository
uses a Git
backend, which is very convenient for managing upgrades and physical
environments, and also for auditing changes. To change the location of
the repository you can set the "spring.cloud.config.server.git.uri"
configuration property in the Config Server (e.g. in
application.yml
). If you set it with a file:
prefix it should work
from a local repository so you can get started quickly and easily
without a server, but in that case the server operates directly on the
local repository without cloning it (it doesn’t matter if it’s not
bare because the Config Server never makes changes to the "remote"
repository). To scale the Config Server up and make it highly
available, you would need to have all instances of the server pointing
to the same repository, so only a shared file system would work. Even
in that case it is better to use the ssh:
protocol for a shared
filesystem repository, so that the server can clone it and use a local
working copy as a cache.
This repository implementation maps the {label}
parameter of the
HTTP resource to a git label (commit id, branch name or tag). If the
git branch or tag name contains a slash ("/") then the label in the
HTTP URL should be specified with the special string "(_)" instead (to
avoid ambiguity with other URL paths). Be careful with the brackets in
the URL if you are using a command line client like curl (e.g. escape
them from the shell with quotes '').
Spring Cloud Config Server supports a single or multiple git repositories:
spring: cloud: config: server: git: uri: https://github.com/spring-cloud-samples/config-repo repos: simple: https://github.com/simple/config-repo special: pattern: pattern*,*pattern1* uri: https://github.com/special/config-repo local: pattern: local* uri: file:/home/configsvc/config-repo
In the above example, if {application}
does not match any of the
patterns, it will use the default uri defined under
"spring.cloud.config.server.git.uri". For the "simple" repository, the
pattern is "simple" (i.e. it only matches one application named "simple").
The pattern format is a comma-separated list of application names with
wildcards (a pattern beginning with a wildcard may need to be quoted).
Note
|
the "one-liner" short cut used in the "simple" example above can only be used if the only property to be set is the URI. If you need to set anything else (credentials, pattern, etc.) you need to use the full form. |
Every repository can also optionally store config files in
sub-directories, and patterns to search for those directories can be
specified as searchPaths
. For example at the top level:
spring: cloud: config: server: git: uri: https://github.com/spring-cloud-samples/config-repo searchPaths: foo,bar*
In this example the server searches for config files in the top level and in the "foo/" sub-directory and also any sub-directory whose name begins with "bar".
By default the server clones remote repositories when configuration is first requested. The server can be configured to clone the repositories at startup. For example at the top level:
spring: cloud: config: server: git: uri: https://git/common/config-repo.git repos: team-a: pattern: team-a-* cloneOnStart: true uri: http://git/team-a/config-repo.git team-b: pattern: team-b-* cloneOnStart: false uri: http://git/team-b/config-repo.git team-c: pattern: team-c-* uri: http://git/team-a/config-repo.git
In this example the server clones team-a’s config-repo on startup before it accepts any requests. All other repositories will not be cloned until configuration from the repository is requested.
To use HTTP basic authentication on the remote repository add the "username" and "password" properties separately (not in the URL), e.g.
spring: cloud: config: server: git: uri: https://github.com/spring-cloud-samples/config-repo username: trolley password: strongpassword
If you don’t use HTTPS and user credentials, SSH should also work out
of the box when you store keys in the default directories (~/.ssh
)
and the uri points to an SSH location,
e.g. "[email protected]:configuration/cloud-configuration". The
repository is accessed using JGit, so any documentation you find on
that should be applicable.
File System Backend
There is also a "native" profile in the Config Server that doesn’t use Git, but just loads the config files from the local classpath or file system (any static URL you want to point to with "spring.cloud.config.server.native.searchLocations"). To use the native profile just launch the Config Server with "spring.profiles.active=native".
Warning
|
The default value of the searchLocations is identical to a
local Spring Boot application (so
[classpath:/, classpath:/config, file:./, file:./config] ) which will
expose the application.properties from the server to all clients.
|
Tip
|
A filesystem backend is great for getting started quickly and for testing. To use it in production you need to be sure that the file system is reliable, and shared across all instances of the Config Server. |
This repository implementation maps the {label}
parameter of the
HTTP resource to a suffix on the search path, so properties files are
loaded from each search location and a subdirectory with the same
name as the label (the labelled properties take precedence in the
Spring Environment).
Health Indicator
Config Server comes with a Health Indicator that checks if the configured
EnvironmentRepository
is working. By default it asks the EnvironmentRepository
for an application named app
, the default
profile and the default
label provided by the EnvironmentRepository
implementation.
You can configure the Health Indicator to check more applications along with custom profiles and custom labels, e.g.
spring: cloud: config: server: health: repositories: myservice: label: mylabel myservice-dev: name: myservice profiles: development
You can disable the Health Indicator by setting spring.cloud.config.server.health.enabled=false
.
Security
You are free to secure your Config Server in any way that makes sense to you (from physical network security to OAuth2 bearer tokens), and Spring Security and Spring Boot make it easy to do pretty much anything.
To use the default Spring Boot configured HTTP Basic security, just
include Spring Security on the classpath (e.g. through
spring-boot-starter-security
). The default is a username of "user"
and a randomly generated password, which isn’t going to be very useful
in practice, so we recommend you configure the password (via
security.user.password
) and encrypt it (see below for instructions
on how to do that).
Encryption and Decryption
Important
|
Prerequisites: to use the encryption and decryption features you need the full-strength JCE installed in your JVM (it’s not there by default). You can download the "Java Cryptography Extension (JCE) Unlimited Strength Jurisdiction Policy Files" from Oracle, and follow instructions for installation (essentially replace the 2 policy files in the JRE lib/security directory with the ones that you downloaded). |
If the remote property sources contain encryted content
(values starting with {cipher}
) they will be decrypted before
sending to clients over HTTP. The main advantage of this set up is
that the property values don’t have to be in plain text when they are
"at rest" (e.g. in a git repository). If a value cannot be decrypted
it is replaced with an empty string, largely to prevent cipher text
being used as a password and accidentally leaking.
If you are setting up a remote config repository for config client
applications it might contain an application.yml
like this, for
instance:
spring: datasource: username: dbuser password: '{cipher}FKSAJDFGYOS8F7GLHAKERGFHLSAJ'
You can safely push this plain text to a shared git repository and the secret password is protected.
The server also exposes /encrypt
and /decrypt
endpoints (on the
assumption that these will be secured and only accessed by authorized
agents). If you are editing a remote config file you can use the Config Server
to encrypt values by POSTing to the /encrypt
endpoint, e.g.
$ curl localhost:8888/encrypt -d mysecret 682bc583f4641835fa2db009355293665d2647dade3375c0ee201de2a49f7bda
The inverse operation is also available via /decrypt
(provided the server is
configured with a symmetric key or a full key pair):
$ curl localhost:8888/decrypt -d 682bc583f4641835fa2db009355293665d2647dade3375c0ee201de2a49f7bda mysecret
Take the encypted value and add the {cipher}
prefix before you put
it in the YAML or properties file, and before you commit and push it
to a remote, potentially insecure store. The /encypt
and /decrypt
endpoints also both accept paths of the form /*/{name}/{profiles}
which can be used to control cryptography per application (name)
and profile when clients call into the main Environment resource.
Note
|
to control the cryptography in this granular way you must also
provide a @Bean of type TextEncryptorLocator that creates a
different encryptor per name and profiles. The one that is provided
by default does not do this.
|
The spring
command line client (with Spring Cloud CLI extensions
installed) can also be used to encrypt and decrypt, e.g.
$ spring encrypt mysecret --key foo 682bc583f4641835fa2db009355293665d2647dade3375c0ee201de2a49f7bda $ spring decrypt --key foo 682bc583f4641835fa2db009355293665d2647dade3375c0ee201de2a49f7bda mysecret
To use a key in a file (e.g. an RSA public key for encyption) prepend the key value with "@" and provide the file path, e.g.
$ spring encrypt mysecret --key @${HOME}/.ssh/id_rsa.pub AQAjPgt3eFZQXwt8tsHAVv/QHiY5sI2dRcR+...
The key argument is mandatory (despite having a --
prefix).
Key Management
The Config Server can use a symmetric (shared) key or an asymmetric one (RSA key pair). The asymmetric choice is superior in terms of security, but it is often more convenient to use a symmetric key since it is just a single property value to configure.
To configure a symmetric key you just need to set encrypt.key
to a
secret String (or use an enviroment variable ENCRYPT_KEY
to keep it
out of plain text configuration files).
To configure an asymmetric key you can either set the key as a
PEM-encoded text value (in encrypt.key
), or via a keystore (e.g. as
created by the keytool
utility that comes with the JDK). The
keystore properties are encrypt.keyStore.*
with *
equal to
-
location
(aResource
location), -
password
(to unlock the keystore) and -
alias
(to identify which key in the store is to be used).
The encryption is done with the public key, and a private key is needed for decryption. Thus in principle you can configure only the public key in the server if you only want to do encryption (and are prepared to decrypt the values yourself locally with the private key). In practice you might not want to do that because it spreads the key management process around all the clients, instead of concentrating it in the server. On the other hand it’s a useful option if your config server really is relatively insecure and only a handful of clients need the encrypted properties.
Creating a Key Store for Testing
To create a keystore for testing you can do something like this:
$ keytool -genkeypair -alias mytestkey -keyalg RSA \ -dname "CN=Web Server,OU=Unit,O=Organization,L=City,S=State,C=US" \ -keypass changeme -keystore server.jks -storepass letmein
Put the server.jks
file in the classpath (for instance) and then in
your application.yml
for the Config Server:
encrypt: keyStore: location: classpath:/server.jks password: letmein alias: mytestkey secret: changeme
Using Multiple Keys and Key Rotation
In addition to the {cipher}
prefix in encrypted property values, the
Config Server looks for {name:value}
prefixes (zero or many) before
the start of the (Base64 encoded) cipher text. The keys are passed to
a TextEncryptorLocator
which can do whatever logic it needs to
locate a TextEncryptor
for the cipher. If you have configured a
keystore (encrypt.keystore.location
) the default locator will look
for keys in the store with aliases as supplied by the "key" prefix,
i.e. with a cipher text like this:
foo: bar: `{cipher}{key:testkey}...`
the locator will look for a key named "testkey". A secret can also be
supplied via a {secret:…}
value in the prefix, but if it is not
the default is to use the keystore password (which is what you get
when you build a keytore and don’t specify a secret). If you do
supply a secret it is recommended that you also encrypt the secrets
using a custom SecretLocator
.
Key rotation is hardly ever necessary on cryptographic grounds if the
keys are only being used to encrypt a few bytes of configuration data
(i.e. they are not being used elsewhere), but occasionally you might
need to change the keys if there is a security breach for instance. In
that case all the clients would need to change their source config
files (e.g. in git) and use a new {key:…}
prefix in all the
ciphers, checking beforehand of course that the key alias is available
in the Config Server keystore.
Tip
|
the {name:value} prefixes can also be added to plaintext posted
to the /encrypt endpoint, if you want to let the Config Server
handle all encryption as well as decryption.
|
Embedding the Config Server
The Config Server runs best as a standalone application, but if you
need to you can embed it in another application. Just use the
@EnableConfigServer
annotation and (optionally) set
spring.cloud.config.server.prefix
to a path prefix, e.g. "/config",
to serve the resources under a prefix. The prefix should start but not
end with a "/". It is applied to the @RequestMappings
in the Config
Server (i.e. underneath the Spring Boot prefixes server.servletPath
and server.contextPath
). Another optional property that can be
useful in this case is spring.cloud.config.server.bootstrap
which is
a flag to indicate that the server should configure itself from its
own remote repository. The flag is off by default because it can delay
startup, but when embedded in another application it makes sense to
initialize the same way as any other application.
Spring Cloud Config Client
A Spring Boot application can take immediate advantage of the Spring
Config Server (or other external property sources provided by the
application developer), and it will also pick up some additional
useful features related to Environment
change events.
Config First Bootstrap
This is the default behaviour for any application which has the Spring
Cloud Config Client on the classpath. When a config client starts up
it binds to the Config Server (via the bootstrap configuration
property spring.cloud.config.uri
) and initializes Spring
Environment
with remote property sources.
The net result of this is that all client apps that want to consume
the Config Server need a bootstrap.yml
(or an environment variable)
with the server address in spring.cloud.config.uri
(defaults to
"http://localhost:8888").
Eureka First Bootstrap
If you are using Spring Cloud Netflix and Eureka Service Discovery, then you can have the Config Server register with Eureka if you want to, but in the default "Config First" mode, clients won’t be able to take advantage of the registration.
If you prefer to use Eureka to locate the Config Server, you can do
that by setting spring.cloud.config.discovery.enabled=true
(default
"false"). The net result of that is that client apps all need a
bootstrap.yml
(or an environment variable) with the Eureka server
address, e.g. in eureka.client.serviceUrl.defaultZone
. The price
for using this option is an extra network round trip on start up to
locate the service registration. The benefit is that the Config Server
can change its co-ordinates, as long as Eureka is a fixed point. The
default service id is "CONFIGSERVER" but you can change that on the
client with spring.cloud.config.discovery.serviceId
(and on the server
in the usual way for a service, e.g. by setting spring.application.name
).
Config Client Fail Fast
In some cases, it may be desirable to fail startup of a service if
it cannot connect to the Config Server. If this is the desired
behavior, set the bootstrap configuration property
spring.cloud.config.failFast=true
and the client will halt with
an Exception.
Config Client Retry
If you expect that the config server may occasionally be unavailable when
your app starts, you can ask it to keep trying after a failure. First you need
to set spring.cloud.config.failFast=true
, and then you need to add
spring-retry
and spring-boot-starter-aop
to your classpath. The default
behaviour is to retry 6 times with an initial backoff interval of 1000ms and an
exponential multiplier of 1.1 for subsequent backoffs. You can configure these
properties (and others) using spring.config.retry.*
configuration properties.
Tip
|
To take full control of the retry add a @Bean of type
RetryOperationsInterceptor with id "configServerRetryInterceptor". Spring
Retry has a RetryInterceptorBuilder that makes it easy to create one.
|
Locating Remote Configuration Resources
The Config Service serves property sources from /{name}/{profile}/{label}
, where the default bindings in the client app are
-
"name" =
${spring.application.name}
-
"profile" =
${spring.profiles.active}
(actuallyEnvironment.getActiveProfiles()
) -
"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
).
Security
If you use HTTP Basic security on the server then clients just need to know the password (and username if it isn’t the default). You can do that via the config server URI, or via separate username and password properties, e.g.
spring: cloud: config: uri: https://user:[email protected]
or
spring: cloud: config: uri: https://myconfig.mycompany.com username: user password: secret
The spring.cloud.config.password
and spring.cloud.config.username
values override anything that is provided in the URI.
If you deploy your apps on Cloud Foundry then the best way to provide the password is through service credentials, e.g. in the URI, since then it doesn’t even need to be in a config file. An example which works locally and for a user-provided service on Cloud Foundry named "configserver":
spring: cloud: config: uri: ${vcap.services.configserver.credentials.uri:http://user:password@localhost:8888}
If you use another form of security you might need to provide a
RestTemplate
to the ConfigServicePropertySourceLocator
(e.g. by
grabbing it in the bootstrap context and injecting one).