Spring Boot app takes 40 seconds to start — how to find what's slow?

Question

Our Spring Boot service's startup has crept up to 40s, which hurts deploys and autoscaling. How do I profile startup?

Accepted Answer

1. **Startup actuator endpoint**: record bean initialization times:

```java
SpringApplication app = new SpringApplication(App.class);
app.setApplicationStartup(new BufferingApplicationStartup(2048));
app.run(args);
```

Then `GET /actuator/startup` lists the slowest steps.

2. Common culprits: Hibernate `ddl-auto=update` or validation on a big schema, classpath scanning over huge packages, eager connections to slow external services, and Flyway migrations.

3. Quick wins:
- `spring.main.lazy-initialization=true` (test it carefully).
- `spring.jpa.open-in-view=false`, and set `ddl-auto` to `none` in production.
- Run on **Java 21+ with Class Data Sharing** (AppCDS). For the biggest gain, consider **GraalVM native image** or **CRaC** (checkpoint/restore).

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