Closer to Code

I'm happy to announce that Karafka 2.6 and Karafka Web UI 1.0 have just been released.

For those new here: Karafka is a Ruby and Rails multi-threaded, efficient Kafka processing framework, and its Web UI is a monitoring and management dashboard that ships alongside it. As with every release in the 2.x line, this is a continuation rather than a rewrite - you upgrade, apply a couple of small changes, and keep going.

On the surface, 2.6 is a focused set of features - redesigned Declarative Topics, dynamic worker pool scaling, a new low-level offsets API, and lag compensation for paused partitions. Underneath, it is the largest internal reorganization the framework has seen in years. Almost none of that groundwork is directly visible to you today, and that is the point: it is the foundation for where Karafka is going next.

This article covers the most significant changes rather than every one. For the full list, the Karafka changelog and Web UI changelog are the source of truth.

The Bigger Picture: Kafka Queues (KIP-932)

Let me start with the direction, because it explains most of this release.

While ago Kafka received a fundamentally new way to consume data. KIP-932 - "Queues for Kafka" - introduced Share Groups, a cooperative model that sits alongside the classic consumer group. Instead of partitions being exclusively assigned to a single consumer, share groups let multiple consumers cooperatively pull from the same partitions and acknowledge individual records. In practice, this brings queue-like semantics to Kafka: work-queue fan-out, per-message acknowledgement, and consumer counts no longer capped by partition count.

The rest of the stack is now catching up to the broker. librdkafka is gaining Share Group support, and I'm building the rdkafka-ruby bindings for it as we speak - the layer Karafka sits on top of. Bringing this all the way up into Karafka is a multi-step journey across the whole stack, and 2.6 is where the framework's part of it begins.

For a framework like Karafka, this is not a small bolt-on. Consumer groups are woven into the fabric of the processing, routing, connection, and instrumentation layers. Share groups need their own parallel strategies, coordinators, jobs, and callbacks - and layering a second, coexisting group type on top cleanly is only possible once the consumer-group-specific code is isolated in its own namespace.

Share Groups are not in 2.6. What is in 2.6 is the mandatory first step: Karafka reorganizes all of those layers into consistent ConsumerGroups namespaces, introduces group-type-agnostic routing accessors, and threads a parallel group / group_id vocabulary through instrumentation payloads. It is deliberately invisible plumbing - and it is what makes Kafka Queues in Karafka tractable rather than a rewrite.

Sponsorship and Community Support

Karafka's progress continues to be powered by the people and companies who fund it, report issues, review pull requests, and run it in production at a scale I could never reproduce alone. To everyone who sponsors the project, contributes code, files detailed bug reports, or helps another user in Slack: thank you. The scope here - dozens of fixes, a major internal reorganization, and the beginning of the Share Groups journey - is only sustainable because Karafka Pro and Enterprise customers let me treat this as serious, ongoing engineering. The more successful the commercial side becomes, the more I can give back to OSS.

Karafka Framework

Redesigned Declarative Topics

The Declarative Topics system now lives in a standalone declaratives.draw DSL, independent of routing.

This resolves a mismatch that grew as adoption spread: many teams use Karafka as the single source of truth for their entire topic infrastructure, not just the topics they consume. Previously, declarations were embedded in routing - so managing a topic (another team's service, a shared audit log, a produce-only sink) meant adding it to your routing, implying consumption intent and dragging all the consumer machinery along. Separating them makes each purpose explicit: routing describes what you consume and how, declaratives describe what topics exist and how they're configured.

class KarafkaApp < Karafka::App
  declaratives.draw do
    defaults do
      replication_factor 3
    end

    topic :orders do
      partitions 6
      config('retention.ms': 86_400_000)
    end

    # Produce-only or owned elsewhere - no routing entry needed
    topic :audit_log do
      partitions 3
      config('cleanup.policy': 'compact')
    end
  end

  routes.draw do
    topic :orders do
      consumer OrdersConsumer
    end
  end
end

The old routing-based config() approach is deprecated but still works in 2.6, so there is no forced migration.

Dynamic Worker Pool Scaling

The worker thread pool can now be scaled at runtime without restarting - handy for time-of-day load, external signals, or ramping up after a deploy.

Karafka::Server.workers.scale(10) # add threads immediately (synchronous)
Karafka::Server.workers.scale(3)  # drain down gracefully (asynchronous)
Karafka::Server.workers.size

Scaling up is synchronous; scaling down lets workers exit as they finish in-flight jobs. Both directions emit worker.scaling.up / worker.scaling.down events. config.concurrency still sets the initial pool size at boot.

Lag Compensation for Long-Paused Partitions

librdkafka refreshes watermark offsets and lag only from fetch responses, so a long-paused partition reports frozen lag in statistics.emitted - and in everything built on it, including the Web UI. Karafka Pro can now compensate: when enabled, it periodically refreshes the watermarks and lags of long-paused partitions through the running connection and overlays them onto the emitted statistics, handing back to live stats on resume. It's opt-in and off by default for now:

config.internal.statistics.consumer_groups.lag_compensation.interval = 30_000
config.internal.statistics.consumer_groups.lag_compensation.pause_age = 30_000

More Robust Error Handling

Two behavioral changes landed in the consumption error path.

• Non-StandardError exceptions (like ScriptError) are no longer silently skipped - they flow through the normal retry / pause / DLQ path.
• Process-critical errors (SystemExit, SignalException, NoMemoryError) are recorded, keep the partition paused, and trigger a graceful shutdown via the auto-subscribed Instrumentation::CriticalErrorsListener rather than being retried or dispatched to a DLQ.

If your consumers can raise non-StandardError exceptions, the outcome now differs from 2.5.

Performance and Ractors

Several internal admin operations that issued N sequential per-partition calls are now single batched calls - watermark reads resolve in two calls regardless of partition count. This is why 2.6 requires karafka-rdkafka >= 0.28.0, which exposes list_offsets and rebuilds consumer #lag on top of it.

Ractor-based parallel deserialization is implemented and works, but I've deliberately held it back from 2.6. This release already carries a large volume of internal change, and stacking Ractors on top would make it much harder to reason about anything that surfaces in production. They'll ship once the 2.6 internals settle - I'd rather isolate risk than bundle two big unknowns into one version.

Karafka Web UI 1.0

After a long run of production-hardened 0.x releases, the Web UI graduates to 1.0.

Why 1.0, and Why Now

The 0.x numbering was always a conservative signal, not a reflection of stability. The Web UI has been production-ready and free of major breaking changes for a very long time, so 1.0 is, first and foremost, an honest version number. There are only small breaking changes in the configuration between 0.11.7 and 1.0. From 3.0 onward, Web UI versioning will align with Karafka's major version and move in lockstep.

Modernized CSRF Protection

The old token-based CSRF approach (route_csrf) is replaced with header-based protection using the browser-enforced Sec-Fetch-Site header (sec_fetch_site_csrf). Modern browsers always send it and it can't be forged cross-origin, so protection is simpler and more robust - with no tokens to thread through your views. For virtually everyone this is transparent; only non-browser clients hitting unsafe methods directly must send Sec-Fetch-Site: same-origin.

Better Monitoring and a More Consistent Interface

• Poll interval monitoring: consumer reporting now tracks poll_interval (max.poll.interval.ms) per subscription group, so you can catch a slow consumer before Kafka evicts it. (Consumer schema bumped to 1.7.0.)
• Runtime-aware worker count: the UI reads the live count from Karafka::Server.workers.size, reflecting dynamic pool scaling accurately.
• Consistency and polish:
  • a standardized empty-state component across every list view
  • topic/partition/offset coordinates in the Explorer and Errors views now link straight to the relevant message
  • Pro gating hardened so a misclick no longer navigates away to an upsell page; rel="noopener noreferrer" on every external link
  • and a whole class of overflow bugs from long topic names fixed.

Dozens of Bug Fixes

Beyond the headline features, this release is genuinely fix-heavy - roughly 30 fixes in Karafka 2.6 and around 25 more in Web UI 1.0. A representative sample from the framework:

• Reset the per-partition retry counter on revocation, so a message reclaimed after a rebalance isn't wrongly treated as retry-exhausted and dispatched to the DLQ early.
• Return false from #mark_as_consumed / #commit_offsets! when the partition was lost (previously could return true in some cases).
• Reset seek_offset only after a successful #seek, so a raising seek no longer skips the rest of a batch.
• Leave tombstone records untouched on encrypted produce/consume instead of crashing, keeping them valid for log compaction (Pro).
• Reset ActiveJob CurrentAttributes in an ensure, so a failed job's attributes no longer leak into the next job.

Upgrade Notes

The 2.5 → 2.6 upgrade is intentionally small for most applications, but there are a few breaking changes, behavioral shifts, and internal namespace moves worth knowing about before you deploy. Web UI 1.0 requires Karafka 2.6, so upgrade them together. Rather than repeat it all here, read the Karafka 2.6 upgrade guide and the Web UI 1.0 upgrade guide - they walk through every required action step by step.

Karafka Pro

Much of the deepest work here - lag compensation, batched Pro iterator resolution, granular backoff correctness, virtual-partition DLQ ordering fixes - lives in Karafka Pro. Pro is what funds this pace of development and how I prioritize the flood of questions and edge cases the community brings. If Karafka is load-bearing infrastructure for you, Karafka Pro pays for itself in features and support - and directly funds the OSS work, including the Share Groups journey ahead.

Summary

Karafka 2.6 is a foundation release. Its visible features - declarative topics, dynamic worker scaling, the offsets API, Pro lag compensation - are useful on their own, but its most important work is the internal reorganization that clears the path for Kafka Queues / Share Groups (KIP-932). Pair that with a 1.0 Web UI that finally carries a version number matching its maturity, plus over fifty bug fixes across both projects, and this release makes the whole ecosystem more solid while setting up what's next.

Thank you to everyone who makes that possible.

References

• Karafka documentation
• Karafka 2.6 upgrade guide
• Web UI 1.0 upgrade guide
• Karafka changelog
• Web UI changelog
• KIP-932: Queues for Kafka

Want to follow the Share Groups work as it lands? Join us in the Karafka Slack channel.