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Requests get dropped during springboot service pod rollout

I am using the Kubernetes cluster with docker. When I deploy the java services[springboot] some requests get dropped(for a couple of secs) with the following error.
exception=org.springframework.beans.factory.BeanCreationNotAllowedException: Error creating bean with name 'controller': Singleton bean creation not allowed while singletons of this factory are in destruction (Do not request a bean from a BeanFactory in a destroy method implementation!), stackTrace=[org.springframework.beans.factory.support.DefaultSingletonBeanRegistry.getSingleton() at line: 208]
I am already using livenessProbe & readinessProbe.
Java Version: 12
SpringBoot Version: 2.1.5.RELEASE
Hibernate Version: 2.4.3 with Postgres DB
As per my knowledge, it is happening due to the closing of the application context while executing some requests. Ideally, it should not be.
can anyone help here ?

the problem is not actually springboot, but rather the way Kubernetes stops pods.
at the moment when a pod from your old deployment/replicaset is being terminated (or rather actually set to state "terminating"), 2 things happen simultaneously:
A) pod is removed from service endpoints, so it does no longer receive new requests
B) pod container gets a SIGTERM, so apps can gracefully shutdown
so what you are seeing here is basically active requests that are being processed when the context gets shut down (as you already found out)
there are (at least) two solutions:
1 in kubernetes pod definition:
Kubernetes pods can be configured with a pre-stop hook that get executes a command in between A and B.
depending on your app, a simple "sleep" for a couple (milli)seconds should be sufficient, leaving the app enough time to finish the current requests before shutting down.
theres nice docu from google that goes more into detail:
https://cloud.google.com/blog/products/containers-kubernetes/kubernetes-best-practices-terminating-with-grace
2 in SpringBoot:
you can make Java wait for finishing up running tasks when receiving the shutdown interrupt.
this is (imho) nicely explained here:
https://www.baeldung.com/spring-boot-graceful-shutdown
Beware: kubernetes default graceful shutdown timeout is 30seconds, then the pod is forcefully removed. but as usual you can configure this timeout in terminationGracePeriodSeconds (also described in the google blog in (1)

How to run a spring boot start up method only once in a multi pod environment

I have a method with #postconstruct annotation , that needs to be executed after application start up. My application is hosted in OS with multiple pods. Now the method gets executed every time a pod starts.But I want it to run only once irrespective of number of instances.

One way you can do this would be for each instance to lookup a record in a shared database and for the pod to lock this record while it executes the method.
Once the executing method has completed, it sets the record with a flag to indicate that the init sequence is complete.
This flag can the be used by instances that did not execute the init method to ignore execution.
Alternatively, if you can restructure your codes, you could use other techniques. e.g this link might be useful
Kubernetes: Tasks that need to be done once per cluster or per statefulset or replicaset

Check for file in intervals until timeout value expired

I'm trying to poll for whether out put file created in a specific directory after a script is invoked in background and then returning from the method execution.
Is that achievable using Timer and Callable. Anything available in spring framework with out using low level Thread.sleep?

How to handle classes that need web resources?

I'm making a project in Java where I have a class that on its initialization connects to an API to retrieve some info. Based on that info it then provides several methods to use and analyse it.
But what if the web request fails ? Or if I have some other issue. Every method will now fail because they don't have the info required
What I did is having a boolean named loadInfo, and also a public method didLoadInfo, so that the client knows the state of the object. I also add a reloadInfo method to try to reload all info, and every method throws an exception if they are called when the loadInfo variable is false. That exception is a checked exception.
Is there another better way to handle this situation ? The exception thrown by all the methods should be checked or unchecked ?
EDIT:
Is a good idea to maintain default values, but how would you let the client know that the info returned may not be up to date ? Maybe another boolean indicating the info state ?

I think in this kind of scenarios you should use REST, so that your java components will be running on web server independently.
If you UI is up and running(it could be on angular or react js or html) and have REST calls in place to call java REST API, also you can configure other API in same web project independent of REST classes and will be initialized as soon at web context is loaded( for example if you are using spring, as soon as application context is loaded).

Since you are calling other services to retrieve info, use Netflix Hysytix to handle failure gracefully with a fallback method. Obviously, you have many more options to fallback logic.
Check out the official Hystrix Library here.
If you have time, check out my article on LinkedIn.

Design Pattern to correctly exit a running program from multiple locations

I have a system written in java where I have multiple distinct objects each with different resources in use. Some have connections to activeMQ queues, some have network connections and others have open files. Some also contain running threads.
When a fatal error occurs anywhere in this system, I need to shut it down and correctly close all resources and stop all running threads.
My problem arises when the object that caused the error needs to start the shutdown process. This object does not know about the other objects that have open files and so on. So it can basically release all its resources and that is it.
I am looking for a clean way to achieve this without getting messy and passing multiple object references around the system.
Any insight is appreciated. Thank you.

Create a central Lifecycle object which all of these other objects in your application have a reference to, and which in turn has a reference to all of these other objects. In addition, each of these objects should implement a common interface such as
public interface ShutdownListener {
void onShutdown();
}
When one of the objects needs to start an orderly shutdown, it can call lifecycle.shutdown() which can in turn call object.onShutdown() on all of the objects registered with it, in order to give these objects a chance to close their resources.
This is basically the Observer pattern.
If you use a dependency-injection container such as Spring, this type of thing is built-in - your beans can extend a certain interface to be notified when the container is shutting down.

You may be able to use Shutdown hook for that. In it you can notify all related objects, which, of course, need to be registered somewhere.

A java virtual machine allows the registration of Shutdown Hooks. Your database connection pool, your file IO manager, your activeMQ queues manager can all independently register their own shutdown hooks that each close all their resources cleanly.
A shutdown hook is a Thread that requires a reference to the resource manager(s) it's responsible for shutting down. The run method of this thread will be executed when the application is terminated. Your application has access to register a shutdown hook anywhere as Runtime.getRuntime() is available as a static call, so no need to wire it into the areas of the application that need it (although it is advisable that you register such shutdown hooks at the time of the creation of each resource manager).
More information here.
http://download.oracle.com/javase/6/docs/api/java/lang/Runtime.html#addShutdownHook(java.lang.Thread)