How to specify external YAML configuration file for springboot

I'm trying to pass in a value to be autowired from a custom configuration file in Spring boot. Below are code snippets:

Spring class

@Configuration
public class MyConfig {

    @Value("${BOOTSTRAP_SERVERS}")
    private String bootstrapServers;

myfile.yaml

BOOTSTRAP_SERVERS: 
  10.0.0.12:9092

Execution command

java  -jar app.jar --spring.config.location=/file/path/myfile.yaml

However when I type the above command I'm getting this error:

java.lang.IllegalArgumentException: Could not resolve placeholder 'BOOTSTRAP_SERVERS' in value "${BOOTSTRAP_SERVERS}"

What am I missing here in order to get this to work? I intend to mount the app in kubernetes so I need to be able to externalize my configuration. Thanks in advance.