A real four-deploy expand-contract migration built with Spring Boot 4.1 and Flyway, proven live against two running replicas with a continuous-traffic load generator: 99.98% success, plus a genuine NOT NULL trap, a backfill-window bug, and H2 silently dropping a concurrently committed row during ALTER TABLE — confirmed to be a database-specific behavior, not a flaw in the technique.
A from-source comparison of Flyway 12.4.0 and Liquibase 5.0.3 on Spring Boot 4.1.1: checksum validation, out-of-order migrations, baselining an existing database, why Flyway Community has no working rollback, Liquibase's very different rollback and locking model, a real Liquibase 5.0.3 defect found and verified during testing, the FSL license change and its fallout at the ASF and Keycloak, and what happens when you run both tools against one database. Every claim traces to a companion project you can clone and run yourself.
A partitioned Spring Batch step scales a 10-million-row job across worker threads — until gridSize doesn't mean what you think, a rejected partition gets stuck forever, and the real speedup tops out well short of 2x.
Spring Boot 4.1 ships Spring Batch 6.0. This article builds a real chunk-oriented import job against a CSV of products, deliberately breaks it on a duplicate row mid-run, and shows exactly what a restart resumes (and what it doesn't) against real captured output: a chunk that commits as a whole or not at all, a second JVM that resumes at row 41 instead of row 1, skip-instead-of-fail as the alternative to restarting, and the resourceless job repository that silently forgets a restart ever happened.
A beginner-first walk through Spring's application-level caching on Spring Boot 4.1.1: what the interceptor actually does, what SimpleKeyGenerator puts in the map, and the four traps that account for most caching bugs — self-invocation, key collisions, eviction timing, and declarations that only fail at the first call. Every figure comes out of a companion project whose 20 tests produce the transcripts. Includes two corrections: @EnableCaching has no exposeProxy attribute, and the documented cache-provider detection order does not match the enum that ships.
Spring Framework 7 ships @Retryable and @ConcurrencyLimit in the core. Every behaviour counted invocation by invocation: a maxRetries that means one more call than you think, a timeout that does not time anything out, jitter that only adds, a CompletableFuture that is never retried, and what is still Resilience4j's job.
Where a Spring Boot 4 error body actually comes from, what spring.mvc.problemdetails.enabled does and does not cover, and a thirteen-failure matrix under five setups, plus the ways a tidy ProblemDetail setup hides 500s, leaks internals, or changed underneath you in Spring Framework 7.
Probes, graceful shutdown, resource limits and JVM ergonomics for Spring Boot 4, measured on a real cluster: a dependency outage under three probe setups, a rolling restart under load four ways, what the JVM decides for nine pod shapes, why CPU limits throttle your garbage collector, and an HPA scaling on a custom Micrometer metric.
One Spring Boot 4 service packaged nine ways (fat jar, layered on Temurin, Alpine and distroless, jlink, the JDK 25 AOT cache, buildpacks and Jib) and measured the same way: size on disk and over the wire, what a one-line change costs to push, startup, who the process runs as, and the failure each variant is most likely to hand you.
All seven propagation values with runnable proof and transaction-manager logs, the rollback rules, and why catching an inner failure still ends in UnexpectedRollbackException. Plus six ways @Transactional is present, correct, and inert — two of which commit work the code was trying to abandon — and why Propagation.NESTED cannot be used with JpaTransactionManager at all. Spring Boot 4.1.1, JDK 25.