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Implement config data loader to load from environment variables

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The config data loader supports the env: prefix and also accepts
extension hints.

Example: env:VAR1[.properties] reads the environment
variable 'VAR1' in properties format (using the
PropertiesPropertySourceLoader).

The PropertySourceLoaders are loaded via spring.factories.

Also adds a smoke test to test it end to end.

Closes gh-41609
This commit is contained in:
Moritz Halbritter
2025-01-30 12:04:05 +01:00
parent 910d57ed90
commit 61d7f3783e
13 changed files with 671 additions and 2 deletions
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32
spring-boot-project/spring-boot-docs/src/docs/antora/modules/reference/pages/features/external-config.adoc
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@@ -354,11 +354,39 @@ spring:
[[features.external-config.files.env-variables]]
=== Using Environment Variables
When running applications on a cloud platform (such as Kubernetes) you often need to read config values that the platform supplies.
You can either use environment variables for such purpose, or you can use xref:reference:features/external-config.adoc#features.external-config.files.configtree[configuration trees].
You can even store whole configurations in properties or yaml format in (multiline) environment variables and load them using the `env:` prefix.
Assume there's an environment variable called `MY_CONFIGURATION` with this content:
[source,properties]
----
my.name=Service1
my.cluster=Cluster1
----
Using the `env:` prefix it is possible to import all properties from this variable:
[configprops,yaml]
----
spring:
config:
import: "env:MY_CONFIGURATION"
----
TIP: This feature also supports xref:reference:features/external-config.adoc#features.external-config.files.importing-extensionless[specifying the extension].
The default extension is `.properties`.
[[features.external-config.files.configtree]]
=== Using Configuration Trees
When running applications on a cloud platform (such as Kubernetes) you often need to read config values that the platform supplies.
It is not uncommon to use environment variables for such purposes, but this can have drawbacks, especially if the value is supposed to be kept secret.
Storing config values in environment variables has drawbacks, especially if the value is supposed to be kept secret.
As an alternative to environment variables, many cloud platforms now allow you to map configuration into mounted data volumes.
For example, Kubernetes can volume mount both https://kubernetes.io/docs/tasks/configure-pod-container/configure-pod-configmap/#populate-a-volume-with-data-stored-in-a-configmap[`ConfigMaps`] and https://kubernetes.io/docs/concepts/configuration/secret/#using-secrets-as-files-from-a-pod[`Secrets`].