Most OpenJDK migrations succeed, but the ones that stall make the same handful of mistakes. They start with a weak inventory, treat the runtime change as a rewrite, leave Oracle Java in the registry, or finish the technical work without ever converting it into renewal leverage. Each is avoidable once you know to look for it.
The most common and most expensive mistake is migrating before you truly know where Java lives. Teams scan the obvious servers, miss the runtimes hidden inside packaged software, build agents, and old desktop installs, and then discover a forgotten Oracle Java dependence late, often during an audit. A weak inventory also hides good news. Many estates are already running free OpenJDK distributions inside platforms and managed services and do not realize it, which means they are preparing to defend exposure they do not have. Begin every migration with a complete inventory that separates genuine Oracle Java from free Java, because every later decision depends on it.
Because the word migration sounds large, teams sometimes plan an OpenJDK move as if it were an application rewrite, with long timelines and heavy risk budgets. For the same Java release it is usually nothing of the sort. OpenJDK and Oracle Java SE are built from the same source, so the large majority of applications run unchanged. Overscoping the work delays the saving, ties up people who are not needed, and can scare an organization out of a move that was always low risk. The right posture is to prove the runtime swap on a pilot, capture it as a repeatable pattern, and roll it out, rather than to treat every workload as a special project.
A tempting mistake is to use the migration as an excuse to retune garbage collection, change flags, and optimize performance across the estate at the same time. This confuses two projects and makes any regression impossible to attribute. Did latency move because of the new runtime or because of the new collector settings? You cannot tell. The disciplined approach is to carry your existing tuning across unchanged, confirm parity under a representative load, and only then, separately, pursue any optimization you want. Keep the migration boring on purpose, because a boring migration is a fast and safe one.
| Mistake | The fix |
|---|---|
| Weak or partial inventory | Scan everything and separate Oracle Java from free Java first |
| Scoping a swap as a rewrite | Prove a pattern on a pilot, then roll it out |
| Retuning during migration | Carry tuning across, optimize later and separately |
| Leaving Oracle images in place | Remove Oracle Java sources so it cannot return |
| No rollback path | Keep a tested rollback on every wave |
| Migrating without leverage | Document the work and use it at renewal |
Teams celebrate a migration and then watch Oracle Java creep back in, because they never removed the sources. If your registry still serves an Oracle Java base image, if your default download still points at an Oracle runtime, or if a build script still fetches one, a new workload will quietly pick it up and your exposure regrows. Closing the door is a deliberate step. Pull the Oracle Java base images, change the defaults to a free OpenJDK distribution, and require a documented exception with a named owner for any new Oracle Java use. A migration that is not governed is a migration that slowly undoes itself.
Confidence on a migration comes from knowing you can reverse a change quickly, not from hoping you will not have to. Teams that skip rollback planning move slowly, because every wave feels irreversible. The fix is cheap. Keep the previous runtime image available, define the conditions that would trigger a rollback, and rehearse the rollback once on the pilot so the team has done it before it matters. In practice rollbacks are rare, because the runtime is equivalent, but the existence of a tested path is what lets a small team move a large estate without hesitation.
The most strategic mistake is technical success that produces no commercial gain. A team migrates most of the estate, then renews with Oracle on the old terms because nobody connected the migration to the negotiation. The migration should be documented and timed so that, when the renewal opens, you can show a shrunken dependence and negotiate the residual against a narrow employee envelope rather than your full headcount. The work on the estate is also the work at the table. Treat them as one program, or you will pay for exposure you no longer have.
A subtle but costly error is treating all Java in the estate as Oracle Java by default. Many runtimes are already free OpenJDK distributions shipped inside platforms, managed services, and tools, and they carry no Oracle dependence at all. Teams that skip this distinction prepare to migrate workloads that need no migration and, worse, prepare to defend exposure they do not have. The opposite error also occurs, where a free looking runtime is in fact an Oracle build pulled in by a default download. The only cure is an inventory that records, for each runtime, which distribution it actually is. Knowing what you really run prevents both wasted migration effort and avoidable audit exposure.
The last few constrained workloads are where momentum dies. The easy wins are banked, attention drifts, and a residual that was meant to be temporary quietly becomes permanent, keeping you tied to Oracle Java and to the per employee metric. The fix is to treat each remaining constraint as a tracked project with an owner and a review date: certify the free runtime with the vendor, upgrade past the issue, or retire the workload. A standing summary of the residual keeps budget and attention on finishing the job. A residual you actively work down is a defensible position. A residual you forget about is a recurring bill.
Underlying several of these mistakes is a single mismatch: teams plan around effort when the cost is driven by dependence. Oracle prices on total employee count, not on how many workloads run Java, so the value of the migration comes from removing dependence, not from touching every machine. Keeping that lens, dependence first, effort second, is what steers a program clear of the busywork that does not move the bill and toward the carve that does.
Consider an anonymized services firm whose first migration attempt stalled. The team had no full inventory, scoped each workload as a rewrite, and tried to retune performance at the same time. Progress was slow and confidence was low. On a reset, they ran a complete inventory, discovered a third of their Java was already free, proved a single base image change on a pilot, and rolled it out without touching tuning. They removed the Oracle base images, documented the result, and used it at the next renewal. The second attempt moved faster than the first had in months. The figures are indicative, but the lesson is that the mistakes, not the technology, were the obstacle.
The opposite of overscoping is letting a migration drift so slowly that it never affects a renewal or an audit. A program with no dates, no owner, and no wave plan can run for years while the per employee bill keeps arriving in full. Slow migrations also lose their leverage, because a vague intention to move someday does not change how Oracle prices you. The fix is to set a realistic timeline, sequence the easy workloads first so progress is visible early, and tie the plan to the renewal calendar. A migration that finishes the bulk of the estate before the next true up is worth far more than a perfect one that arrives after the contract has already been signed on the old terms.
OpenJDK migrations rarely fail on technology. They stall on a weak inventory, an overscoped plan, retuning during the move, an open door for Oracle Java to return, no rollback path, or a failure to convert the work into renewal leverage. Avoid those and the migration is straightforward.
Avoiding these mistakes is what keeps a migration on track. For the full method see the OpenJDK Migration Playbook. For the governance that closes the door for good, read about OpenJDK migration governance and standards, and for the safety net that lets you move fast, see rollback planning for a Java migration.
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