An application listening on a port is not necessarily ready for meaningful traffic. Readiness must reflect required initialization without making restart decisions depend on every transient outage.
Before you start
You should know Java classes, dependency injection and basic HTTP requests. Identify where a call crosses a framework-managed boundary. The snippets illustrate a focused mechanism; database configuration, application wiring and authentication must be supplied by the surrounding application when applicable.
The practical goal is to reason through this situation: A service becomes ready after essential initialization and becomes unready during draining. Read the walkthrough first, then try the interview exercise before opening its answer. The important part is explaining the decision and its consequences, rather than remembering a definition alone.
Step-by-step walkthrough
Step 1: Allow essential initialization
A bound port alone does not prove the application can serve useful work.
Step 2: Separate probe purposes
Startup allowance, liveness and readiness answer different lifecycle questions.
Step 3: Model draining and outages
Become unready before shutdown and avoid shared-dependency restart storms.
Worked scenario
A service becomes ready after essential initialization and becomes unready during draining.
A service starts listening before cache initialization completes. Readiness remains false until required initialization succeeds, while startup policy gives it a reasonable window. Later database failure can make it unready without necessarily declaring the process dead; during draining it stops new traffic while finishing active work.
Common mistake
Using dependency availability as liveness can restart all instances during a shared outage.
Verify the behavior
Test slow initialization, dependency outage, recovery and graceful rollout behavior.
Interview exercise
Define deployment probes.
Answer and reasoning
Separate startup allowance, liveness and readiness, then test rollout and shutdown behavior under dependency failures.
Continue learning
Compare the scenario with the Spring Boot interview questions and test your understanding with the Spring Boot MCQs. For terminology and implementation details, consult the reference material.