Options for dynamic properties in Spring Boot

Question

I have an application with some externalized configuration in the form of properties. I would like the application to react to a change of such properties without a restart or full context refresh.

I am not clear what my options are.

Artificial example: the application implements a service that receives requests and decides whether to queue or reject them. The maximum size of the queue is a property.

final int queueMaxSize = queueProperties.getMaxSize();
if (queue.size() >= queueMaxSize) { //reject }

Where QueueProperties is a class annotated with @ConfigurationProperties.

@ConfigurationProperties(prefix = "myapp.limits.queue")
@Getter
@Setter
public class QueueProperties {
  public int maxSize = 10;
}

This works as far as allowing me to control behavior via system properties, profiles, etc. However, I would like to be able to change this value without releasing/deploying/restarting/refreshing the application.

My application already uses Archaius. If I push a new value for this property using our internal infrastructure, i can see the application Spring Environment does receive the new value. (e.g., /admin/env reflects the value and changes dynamically).

The part I'm not clear on is: how to make my service react to the change of value in the environment?

I found two ways, but they seem hairy, I wonder if there are better options. I expected this to be a common problem with a first class solution in the Spring ecosystem.

Hacky solution #1:

@Bean
@Scope("prototype")
@ConfigurationProperties(prefix = "myapp.limits.queue")
QueueProperties queueProperties() {
    return new QueueProperties();
}

And inject this into the service using the properties as Provider and use it as queuePropertiesProvider.get().getMaxSize().

This works but has a few side-effects I'm not a fan of:

ConfigurationProperties annotation moved from the class to the bean definition
A new QueueProperties object is created and bound to values for every request coming in
Provider might throw on get()
Invalid values are not detected until the first request comes in

Hacky solution #2:

Don't annotate my properties class with ConfigurationProperties, inject the Spring environment at construction time. Implement the getters as such:

int getMaxSize() {
   return environment.getProperty("myapp.limits.queue", 10);
}

This also works ok in terms of behavior. However - This is not annotated as property (unlike the rest of the properties classes in this large project, makes it harder to find) - This class does not show up in /admin/configprops

Hacky solution #3:

Schedule a recurring task that uses Environment to update my singleton QueueProperties bean.

Any further ideas/suggestions/pointers? Is there a canonical/recommended way to do this that does not have the shortcoming of my solutions above?

Options for dynamic properties in Spring Boot

0 Answers