# Client versions (/connectors/kafka/how-to/client-versions)



Any Kafka client built for **Kafka 0.11 (2017) or later** works. That covers every client release of
the last several years; the floor matters only for very old applications and for libraries whose
defaults still pretend to be old.

## The floor, and why [#the-floor-and-why]

KubeMQ stores record batches in the format Kafka introduced in 0.11 and serves the protocol from
there:

| Request         | Oldest version served | Why                                                                                                  |
| --------------- | --------------------- | ---------------------------------------------------------------------------------------------------- |
| Produce         | v3                    | the first version carrying the 0.11 record-batch format — the only format stored                     |
| Fetch           | v4                    | the first version that returns that format; an older consumer would be handed bytes it cannot decode |
| OffsetFetch     | v2                    | the first version that can report an error; older versions would turn an error into a silent success |
| ListOffsets     | v0                    | every version, from next v1.2.0 — see below                                                          |
| Everything else | v0                    |                                                                                                      |

A client older than the floor negotiates, finds no common version, and fails at connect time rather
than misbehaving later. The full per-request table is in
[Capabilities](/connectors/kafka/reference/capabilities).

**librdkafka 1.7 and older** (Confluent's `cp-kcat:7.6.1` image, and Python, Go and .NET clients
built on that release) ask for ListOffsets v0 when a consumer starts from the earliest or latest
offset. From **next v1.2.0** that is served. On next v1.1.0 and earlier the client fails every
consume locally with `Failed to query logical offset END: Required feature not supported by
broker` — no request reaches the server, so nothing appears in its log. Upgrade the client or the
server.

**Sarama** chooses its protocol from `Config.Version`, not by negotiation. Set it to your real
target, `sarama.V2_8_0_0` or later is a safe choice, or an old default can select a request version
below the floor.

## Consumer group protocol [#consumer-group-protocol]

The next-generation consumer group protocol (KIP-848, `group.protocol=consumer`) is not served.
Clients default to the classic protocol, which is fully supported; an application that opted in to
the new one must set `group.protocol=classic`.

## Clients that have been run against KubeMQ [#clients-that-have-been-run-against-kubemq]

| Client                                                    | Version      | How                                                                                                                                                                |
| --------------------------------------------------------- | ------------ | ------------------------------------------------------------------------------------------------------------------------------------------------------------------ |
| Java `kafka-clients`                                      | 3.7.1        | the application simulator: admin, idempotent and transactional producers, 3-member groups, all four codecs, on a 3-node cluster with the leader killed mid-traffic |
| `confluent-kafka` (Python) / librdkafka                   | 2.6.1        | the same simulator                                                                                                                                                 |
| librdkafka (`kcat`)                                       | 1.7.0, 1.8.2 | produce, consume and consumer groups                                                                                                                               |
| Kafka Connect, Kafka Streams                              | 3.9.1        | see [Kafka Connect](/connectors/kafka/how-to/kafka-connect) and [Kafka Streams](/connectors/kafka/how-to/kafka-streams)                                            |
| franz-go, Sarama, segmentio/kafka-go, the Kafka CLI tools | current      | the conformance suite, compared request by request against Apache Kafka                                                                                            |

A client not in the table is not assumed broken — the protocol surface above is what decides — but
run your own application once against a test cluster before cutting over. The simulator in the
server repository (`tests/kafka-app-sim`) is built for exactly that: it runs an ordinary application
against Apache Kafka first, then against KubeMQ, and checks loss, duplicates, ordering and
exactly-once in between.