View Source KafkaEx Changelog

1.0.1 (2026-06-26)

Breaking Changes

  • KafkaEx.API.start_client/1 no longer registers globally by default. Previously start_client() (no :name argument) silently registered the GenServer as KafkaEx.Client, while the documented :name option was ignored. Two callers collided with :already_started.

    Now start_client() returns {:ok, pid} unnamed. To preserve the old behavior explicitly:

    KafkaEx.API.start_client(name: KafkaEx.Client)

    :name accepts any GenServer.name() shape: an atom, {:global, term}, or {:via, Module, term}. See UPGRADING.md for the full migration. Most callers bind the returned pid ({:ok, client} = start_client(...)) and are unaffected.

  • Consumer auto_offset_reset now defaults to :latest (was :none), matching the Kafka/Java client default, and :none now raises instead of silently starting a fresh consumer group from the earliest offset. This only affects a consumer with no valid committed offset that does not set auto_offset_reset explicitly: a new consumer group now consumes only new messages (previously it silently replayed the whole topic), and an out-of-range offset now resets to latest (previously it raised). Set auto_offset_reset: :earliest to keep replaying from the beginning, or :none for the strict raise-on-bad-offset behavior. An invalid value now fails fast at consumer start. See UPGRADING.md.

Fixed

  • KafkaEx.API.start_client/1 and child_spec/1 now merge config.exs defaults and accept the documented :brokers option (#538). Previously start_client(brokers: [...]) crashed with InvalidConsumerGroupError: nil because config defaults were never merged and the :brokers key was ignored (the client read :uris). :brokers is now the canonical key; :uris is a deprecated-but-working alias. start_client/1 returns {:error, :invalid_consumer_group} on a bad group; child_spec/1 raises KafkaEx.InvalidConsumerGroupError at spec-build time.

  • KafkaEx.API.fetch/5 (and KafkaEx.Consumer.Stream) hang at logend. Previously the GenServer.call default timeout (5s) and the per-broker Socket.recv timeout (1-3s from sync_timeout config) were not aligned with the user-supplied :max_wait_time (default 10s). The broker held the long-poll for up to 10s; both upper timeouts fired first, causing socket close → reconnect → retry 3 times, every retry hitting the same mismatch.

    Now KafkaEx.API.fetch/5 derives both timeouts from :max_wait_time automatically (network_timeout = max_wait_time + 5_000, call_timeout = network_timeout × 3 + 5_000). The × 3 multiplier covers the Client's retry budget so the GenServer.call does not exit while retries are still in flight. Users who bumped sync_timeout as a workaround can revert.

    Two related stream bugs also fixed:

    • KafkaEx.Consumer.Stream no longer silently spins when a fetch returns an error and no_wait_at_logend: false. The stream halts and emits a Logger.warning with the error code.
    • auto_commit: true + error response no longer raises KeyError on fetch_response.message_set. need_commit?/2 returns false for error responses, so no commit is attempted.

  • KIP-394 two-step JoinGroup no longer retries on :member_id_required (#541). The generic retry loop treated :member_id_required as a transient error and blindly re-sent the identical request, which the broker rejected again. JoinGroup now uses a dedicated KafkaEx.Support.Retry.join_group_retryable?/1 classifier that returns false for :member_id_required, so the two-step path swaps in the broker-assigned member_id and rejoins as KIP-394 intends. Required for correct interop with Kafka 2.3+ under group.initial.rebalance.delay.ms.

  • Consumer-group heartbeat and SyncGroup errors now rejoin or stop cleanly instead of crashing the group (#554, #555). Previously :illegal_generation / :unknown_member_id / :fenced_instance_id reached the manager as a generic error and crashed it under the one_for_all / max_restarts: 0 consumer-group supervisor, escalating one member's stale generation into a group-wide rebalance. Now, matching brod's identity handling (terminal codes follow the Java client):

    • :illegal_generation → rejoin keeping member_id (only the generation is stale).
    • :unknown_member_id → rejoin after clearing member_id (the coordinator forgot the member; the broker assigns a fresh one).
    • :fenced_instance_id (KIP-345) and :group_authorization_failed → clean terminal stop without rejoining (rejoining would split-brain the static slot or fail authorization again).

    Stale heartbeat-timer EXITs (from a timer already replaced during a rebalance) are dropped instead of acted on. A {:heartbeat_rejoin, reason} reason is emitted on the [:kafka_ex, :consumer, :rebalance] telemetry event.

  • Client retry loop preserves the real transport error atom (#544). A recv timeout to a broker was mapped to :unknown, which crashed the consumer-group manager via SyncGroupError (the rebalance-storm root cause). The actual transport atom (:timeout, :closed, …) is now kept so it is classified and recovered correctly.

  • Consumer-group sync recovery is bounded, not crash-on-error (#546). Recoverable SyncGroup errors now rejoin with a bounded retry budget and generation reset between attempts instead of raising and tearing down the group supervisor.

  • The group coordinator is re-discovered on :not_coordinator / :coordinator_not_available (#547). Previously a stale cached coordinator was reused after the coordinator moved (rolling restart), so every subsequent request failed. The cached coordinator is now invalidated and rediscovered.

  • OffsetCommit / OffsetFetch correctness — no silent loss or duplicate processing (#548). The stream halts on a fatal commit error instead of looping and reprocessing; load_offsets retries retryable errors (including :unstable_offset_commit, KIP-447) and raises on fatal/exhaustion instead of silently resetting to the earliest offset.

  • Broker connect is bounded by a timeout instead of blocking indefinitely (#556). Connecting to an unreachable broker no longer hangs the client; the connect is bounded by :connect_timeout (default 10s).

  • Transaction control batches are dropped from fetch results, and the fetch offset advances past them (#557). Control batches (transaction commit/abort markers) were surfaced to consumers as records; they are now filtered out. A fetch that contains only control batches still advances the consumer/stream offset past them (via the batch metadata) instead of re-fetching the same offset forever.

Internal

  • Consumer-group / config test stabilization: eliminated the on_exit teardown :noproc race class via KafkaEx.TestSupport.ProcessHelpers and stabilized three flaky consumer-group / config tests (#549, #553).
  • load_offsets startup retry now rides the unified KafkaEx.Support.Retry.with_retry/2 with exponential backoff (#551).
  • Renamed the KafkaEx.Support.Retry option :max_retries to :max_attempts for consistency with the retry-count semantics (#552).
  • Migrated the test suite's mocking from Hammox to Mimic (mimic ~> 1.7), dropping the unused KafkaEx.NetworkClientMock. No runtime/production changes. (#534)
  • Added regression test coverage pinning previously-untested behavior: remote-close (:tcp_closed/:ssl_closed) handling and its telemetry in KafkaEx.Client (#449), init fail-fast when all brokers are unreachable (#298), and cross-topic response identity on a single client (#445). (#535)

1.0.0

Single release entry accumulates all post-rc.2 work. RC tags along the way (rc.3, rc.4, …) share this entry — individual rc entries are not maintained.

Breaking Changes

  • Produce headers API — the headers: option on KafkaEx.API.produce/4,5, produce_one/4,5, and produce_sync/4,5 now requires [%KafkaEx.Messages.Header{}] structs instead of [{binary, binary}] tuples. Brings the produce path in line with the fetch path, which already returned %Header{} structs.

    Before:

    KafkaEx.API.produce(client, "t", 0, [
  %{value: "v", headers: [{"key", "val"}]}
])

    After:

    alias KafkaEx.Messages.Header
KafkaEx.API.produce(client, "t", 0, [
  %{value: "v", headers: [Header.new("key", "val")]}
])

    Silent-at-compile, fails-at-runtime with FunctionClauseError — see UPGRADING.md for the migration pattern.

Fixed

  • Consumer group no longer silently consumes on stale generation after a non-retryable OffsetCommit error. Previously :illegal_generation (and siblings) were logged and swallowed; the consumer kept running on a stale generation until the next heartbeat happened to also fail, potentially many seconds of zombie operation. Now classified across three paths matching Java ConsumerCoordinator, librdkafka rdkafka_cgrp, brod brod_group_coordinator, and kafka-python:

    • Terminal — :fenced_instance_id (KIP-345), :group_authorization_failed, :topic_authorization_failed, :offset_metadata_too_large, :invalid_commit_offset_size. Consumer stops without rejoining.
    • Fatal — :illegal_generation, :unknown_member_id. GenConsumer casts {:rejoin_required, reason, stale_gen} to the group manager (with mailbox coalescing for multi-partition storms), self-stops with {:shutdown, {:rejoin_required, _}}. Manager resets member_id / generation_id and rebalances. Under restart: :transient the supervisor does not respawn the stopped worker; the rebalance spawns a fresh one.
    • Retryable — :rebalance_in_progress (flag-and-wait; heartbeat path drives the eventual rebalance, matching Java), :unstable_offset_commit (KIP-447), and standard transient errors.

    At-least-once semantics preserved. See UPGRADING.md for details.

  • Bootstrap crash when api_version was set explicitly and the broker map was empty — the client now honors the explicit override instead of returning :api_not_supported_by_broker.

  • Record-header encoding in V3+ record batches (per-record headers were previously dropped).

  • Version-0 falsy bug in get_api_version — V0 was treated as "unset" and fell through to the hardcoded default.

Added

  • KIP-394 two-step JoinGroup. Client auto-retries JoinGroup with the broker-assigned member_id on :member_id_required. Required for interop with Kafka 2.3+ under group.initial.rebalance.delay.ms.

  • KIP-345 batch LeaveGroup V3+. LeaveGroup sends the members array for V3+ brokers.

  • 3-tier API version resolution.

    1. Per-request :api_version option
    2. Application config api_versions: %{...} map
    3. Broker-negotiated max (min(broker_max, kayrock_max))

    Replaces hardcoded defaults that ignored broker capability. Previously produce/fetch used v3 regardless of what the broker supported; now a Kafka 3.x broker will get the full API surface.

  • KafkaEx.Support.VersionHelper.maybe_put_api_version/3 — internal helper for consumer/stream callers. Thin wrapper over the 3-tier resolution.

  • [:kafka_ex, :consumer, :commit_failed] telemetry event. Emitted on every commit-error branch (terminal / fatal / transient) with metadata %{group_id, topic, partition, offset, kind, error}. Parity stand-in for Java's CommitFailedException — subscribe to the event to observe commit failures.

  • Retry classifiers. KafkaEx.Support.Retry.commit_fatal_error?/1 and commit_terminal_error?/1 — mirrors the reference-client error taxonomy.

Changed

  • Test infrastructure. Process.sleep(50) replaced with MockClient.wait_for_calls/3 polling helper for deterministic unit tests. Adds lifecycle integration tests for the 3-tier version resolution and the :illegal_generation rejoin loop.

  • Integration + chaos coverage for Phase B. Live-broker integration tests for rejoin_required cast handling, plus a Testcontainers-isolated chaos test that fires a 30-second storm of fatal casts and asserts the mailbox-drain coalescing ratio.

Removed

  • :consumer_group_update_interval config option (and corresponding Client.State field). The value was silent-ignored long before 1.0; removed to clean up the config surface. No runtime impact — consumer-group polling cadence is driven by heartbeat/session-timeout, which remain configurable.

Migration

See UPGRADING.md.

1.0.0-rc.2 - 2026-03-15

Fixed

  • ConsumerGroupDescription.Member.member_assignment now returns an empty %MemberAssignment{version: 0, user_data: <<>>, partition_assignments: []} struct instead of nil when Kafka returns a null or empty member assignment (e.g., during rebalancing). This prevents KeyError crashes when accessing .partition_assignments on the result. Breaking: code that pattern-matches on member_assignment: nil or checks == nil must be updated to check for an empty partition_assignments list instead.

Changed

  • MemberAssignment defstruct now has explicit defaults (version: 0, partition_assignments: [], user_data: <<>>) matching its typespec.
  • Type specs for Member.t() and Member.assignment/1 no longer include | nil for the member_assignment field.

1.0.0-rc.1 - 2026-02-15

Breaking Changes

  • Removed legacy server implementations (Server0P8P0, Server0P8P2, Server0P9P0, Server0P10AndLater)
  • Removed kafka_version configuration option - Kayrock is now the only implementation
  • Kayrock is now the default and only client implementation
  • Module reorganization:

Added

  • KafkaEx.API module as primary API with explicit client-based functions
  • Automatic API version negotiation with Kafka brokers
  • Full message headers support
  • SASL authentication support (PLAIN, SCRAM-SHA-256, SCRAM-SHA-512, OAUTHBEARER, MSK_IAM)
  • Telemetry support for request lifecycle monitoring and observability
  • Heartbeat API (v0-v4) with full version support
  • LeaveGroup API (v0-v4) with full version support
  • SyncGroup API (v0-v4) with full version support
  • Graceful shutdown for GenConsumer
  • Compression support (gzip, snappy, lz4, zstd)

Changed

  • All functions now use Kayrock for protocol handling
  • Improved error handling with structured errors (KafkaEx.Client.Error)
  • Codebase reorganized by domain (cluster, client, consumer, producer, messages)
  • Test structure reorganized to match new module organization

Removed

  • Legacy KafkaEx.produce/4 and KafkaEx.fetch/3 - use KafkaEx.API functions
  • KafkaEx.Server0P8P0, KafkaEx.Server0P8P2, KafkaEx.Server0P9P0, KafkaEx.Server0P10AndLater
  • kafka_version configuration option
  • Legacy snappy-erlang-nif dependency (snappyer is now the default)

Migration

See UPGRADING.md for detailed migration instructions.

0.14

Fixes

  • Multiple Github Action Fixes
  • Fix deprecation warnings with Bitwise usage
  • Fix deprecation warnings with Config
  • Fix deprecation warnings with Stacktrace

Features

  • Added describe_groups API

Breaking Changes

  • Set minimal version of elixir to 1.8

0.13

  • Support Snappyer 2
  • Continuous integration: replace CircleCI
  • Using the Kayrock client: take into account the api_version when retrieving offsets to fetch messages.
  • Update metadata before topic creation to make sure it connects to a controller broker.
  • Support record headers.

0.12.1

Increases the version of ex_doc to allow publishing

Includes all the 0.12.0 changes.

0.12.0

NOTE: not released due to issues with ex_doc.

Breaking Changes

  • Drop support for Elixir 1.5

Features

  • Allow passthrough of ssl_options when starting a consumer or consumer group (#413)
  • Allow GenConsumer callbacks to return :stop - allows graceful shutdown of consumers (#424)

Bugfixes

Misc

  • Use Dynamic Supervisor rather than simple_one_for_one - fixes warnings on newer elixir versions (#418)
  • Update to Kayrock 0.1.12 - fix compile warnings (#419)
  • Tests pass the first time more often now (#420)
  • Fix deprecation warning about Supervisor.terminate_child (#430)
  • Remove Coveralls - was not being used, caused test failures (#423)

PRs Included

  • #413
  • #418
  • #419
  • #420
  • #430
  • #423
  • #424

0.11.0

KafkaEx 0.11.0 is a large improvement to KafkaEx that sees the introduction of the Kayrock client, numerous stability fixes, and a critical fix that eliminates double-consuming messages when experiencing network failures under load.

Breaking changes

  • Drop support for Elixir < 1.5
  • Partitioner has been fixed to match the behavior of the Java client. This will cause key assignment to differ. To keep the old behavior, use the KafkaEx.LegacyPartitioner module. (#399)

Fixes

  • Numerous fixes to error handling especially for networking connections (#347, #351 )
  • Metadata is refreshed after topic create/delete(#349)
  • Compression actually works for producing now 😬 (#362)
  • Don't crash when throttled by quotas (#402)
  • Default partitioner works the same way as the Java client now (#399)
  • When fetching metadata for a subset of topics, don't remove the metadata for the unfetched topics. (#409)

Improvements

  • Any GenServer can be used as a KafkaEx.GenConsumer (#339)
  • Can specify wait time before attempting reconnect (#347)
  • KafkaEx.stream/3 now uses the KafkaEx.Server interface, which inherits the sync_timeout setting. This avoids timeouts when sync_timeout needs to be greater than default. (#354)
  • KafkaEx can now use Kayrock as the client implementation. This is a large change, and is pushing toward the improvements we want in 1.0 to allow the library to easily support new versions of the Kafka protocol. (#356, #359, #364, #366, #367, #369, #370, #374, #375, #377, #379, #387, #406, #408)
  • KafkaEx.Protocol.Fetch.Message includes the topic and partition, allowing consumers to know which topic and partition they consumed from.
  • Add KafkaEx.start_link_worker/1-2 to start a working and link it to the current process.
  • Allow setting the client_id for the application - supports better monitoring, debugging, and quotas. (#388)
  • Send metadata requests to a random broker rather than the same one each time (#395)
  • Retry joining a consumer group 6 times rather than failing (#375, #403)

Kayrock client

See Kayrock and the Future of KafkaEx

Note that the Kayrock implementation doesn't support Kafka < 0.11

Improvements over default client:

  • Can specify message API versions for the KafkaEx.stream/3 API
  • Can specify message API versions for the consumer group API - NOTE that if you specify OffsetCommit API version >= 2, it will attempt to store the offsets in kafka, which will have no data about the topic unless you migrate the data. This could result in losing or reprocessing data. Migration can be done out of band, or can be done via the appropriate API calls within KafkaEx.
  • Allow specifying OffsetCommit API version in KafkaEx.fetch

Misc

  • Test suite uses KafkaEx 0.11 now in preparation for fully supporting Kafka API versions.
  • KafkaEx.Protocol.Produce cleaned up (#380)
  • Documentation improvements (#383, #384)
  • Test against Elixir 1.9 (#394)
  • Use OTP 22.3.3+ for OTP 22.2 testing to avoid SSL bug. (#405)

0.10.0

Features

  • Allow passing in state to a KafkaEx.GenConsumer by defining a KafkaEx.GenConsumer.init/3 callback. Adds a default implementation of init/3 to ensure backward compatibility. -- @mtrudel
  • Support DeleteTopics API for Kafka 0.10+ -- @jbruggem
  • Add a default partitioner using murmur2 hashing when key is provided, or random partitioning otherwise. Use the KafkaEx.Partitioner behaviour to define a different partitioner, and enable it by adding it to the partitioner configuration setting.

Misc

  • Lots of documentation fixes
  • Fixing elixir 1.8 compile warnings

PRs Included:

  • #343
  • #338
  • #337
  • #335
  • #329
  • #333
  • #331

Previous Versions

See the releases for change notes.