How to read secret key and value from Kubernetes volume mount using Spring Boot - spring

Question

I have mounted one volume which contained username and password inside pod. If I do:
kubectl exec -it my-app -- cat /mnt/secrets-store/git-token
{"USERNAME":"usernameofgit","PASSWORD":"dhdhfhehfhel"}
I want to read this USERNAME and PASSWORD using Spring Boot.

Answer 1

Assuming:
the file (git_token) format is fixed (JSON).
the file may not have an extension suffix (.json).
... we have some Problems!
I tried 2.3.5. Importing Extensionless Files like:
spring.config.import=/mnt/secrets-store/git-token[.json]
But it works only with YAML/.properties yet!(tested with spring-boot:2.6.1))
Same applies to 2.8. Type-safe Configuration Properties. ;(;(
In Spring-Boot we can (out-of-the box) provide JSON-config (only) as SPRING_APPLICATION_JSON environment/command line property, and it has to be the json string, and cannot be a path or file (yet).
The proposed (baeldung) article shows ways to "enable JSON properties", but it is a long article with many details, shows much code and has decent lacks/outdates (#Component on #ConfigurationProperties is rather "unconventional")..
I tried the following (on local machine, under the mentioned assumptions):
package com.example.demo;
import com.fasterxml.jackson.annotation.JsonProperty;
import lombok.Data;
import org.springframework.beans.factory.annotation.Value;
import org.springframework.boot.CommandLineRunner;
import org.springframework.boot.SpringApplication;
import org.springframework.boot.autoconfigure.SpringBootApplication;
import org.springframework.context.annotation.Bean;
#SpringBootApplication
public class DemoApplication {
public static void main(String[] args) {
SpringApplication.run(DemoApplication.class, args);
}
#Value("""
#{#jacksonObjectMapper.readValue(
T(java.nio.file.Files).newInputStream(
T(java.nio.file.Path).of('/mnt/secrets-store/git-token')),
T(com.example.demo.GitInfo)
)}""" // watch out with #Value and text blocks! (otherwise: No converter found capable of converting from type [com.example.demo.GitInfo] to type [java.lang.String])
)
GitInfo gitInfo;
#Bean
CommandLineRunner runner() {
return (String... args) -> {
System.out.println(gitInfo.getUsername());
System.out.println(gitInfo.getPassword());
};
}
}
#Data
class GitInfo {
#JsonProperty("USERNAME")
private String username;
#JsonProperty("PASSWORD")
private String password;
}
With (only) spring-boot-starter-web and lombok on board, it prints the expected output.
Solution outline:
a pojo for this
the upper case is little problematic, but can be handled as shown.
a (crazy) #Value - (Spring-)Expression, involving:
(hopefully) auto-configured #jacksonObjectMapper bean. (alternatively: custom)
ObjectMapper#readValue (alternatives possible)
java.nio.file.Files#newInputStream (alternatives possible)
java.nio.file.Path#of

Answer 2

When you have your volume mounted, then all you need to do is to read a JSON file from the Spring Boot application. I recommend reading Load Spring Boot Properties From a JSON File.
In short, you can create a class corresponding to your JSON file, something like this one.
#Component
#PropertySource("file:/mnt/secrets-store/git-token")
#ConfigurationProperties
public class GitToken {
private String username;
private String password;
// getters and setters
}
Then, you need to add it to componentScan and you can autowire your class.