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kafka

The kafka output type writes a batch of messages to Kafka brokers and waits for acknowledgement before propagating it back to the input.

# Common config fields, showing default values
output:
  label: ""
  kafka:
    addresses: [] # No default (required)
    topic: "" # No default (required)
    target_version: 2.1.0 # No default (optional)
    key: ""
    partitioner: fnv1a_hash
    compression: none
    static_headers: {} # No default (optional)
    metadata:
      exclude_prefixes: []
    max_in_flight: 64
    batching:
      count: 0
      byte_size: 0
      period: ""
      jitter: 0
      check: ""

The config field ack_replicas determines whether we wait for acknowledgement from all replicas or just a single broker.

Both the key and topic fields can be dynamically set using function interpolations described here.

Metadata will be added to each message sent as headers (version 0.11+), but can be restricted using the field metadata.

Strict Ordering and Retries​

When strict ordering is required for messages written to topic partitions it is important to ensure that both the field max_in_flight is set to 1 and that the field retry_as_batch is set to true.

You must also ensure that failed batches are never rerouted back to the same output. This can be done by setting the field max_retries to 0 and backoff.max_elapsed_time to empty, which will apply back pressure indefinitely until the batch is sent successfully.

However, this also means that manual intervention will eventually be required in cases where the batch cannot be sent due to configuration problems such as an incorrect max_msg_bytes estimate. A less strict but automated alternative would be to route failed batches to a dead letter queue using a fallback broker, but this would allow subsequent batches to be delivered in the meantime whilst those failed batches are dealt with.

Troubleshooting​

If you're seeing issues writing to or reading from Kafka with this component then it's worth trying out the newer kafka_franz output.

  • I'm seeing logs that report Failed to connect to kafka: kafka: client has run out of available brokers to talk to (Is your cluster reachable?), but the brokers are definitely reachable.

Unfortunately this error message will appear for a wide range of connection problems even when the broker endpoint can be reached. Double check your authentication configuration and also ensure that you have enabled TLS if applicable.

Performance​

This output benefits from sending multiple messages in flight in parallel for improved performance. You can tune the max number of in flight messages (or message batches) with the field max_in_flight.

This output benefits from sending messages as a batch for improved performance. Batches can be formed at both the input and output level. You can find out more in this doc.

Fields​

addresses​

A list of broker addresses to connect to. If an item of the list contains commas it will be expanded into multiple addresses.

Type: array

# Examples

addresses:
  - localhost:9092

addresses:
  - localhost:9041,localhost:9042

addresses:
  - localhost:9041
  - localhost:9042

tls​

Custom TLS settings can be used to override system defaults.

Type: object

tls.enabled​

Whether custom TLS settings are enabled.

Type: bool
Default: false

tls.skip_cert_verify​

Whether to skip server side certificate verification.

Type: bool
Default: false

tls.enable_renegotiation​

Whether to allow the remote server to repeatedly request renegotiation. Enable this option if you're seeing the error message local error: tls: no renegotiation.

Type: bool
Default: false
Requires version 1.0.0 or newer

tls.root_cas​

An optional root certificate authority to use. This is a string, representing a certificate chain from the parent trusted root certificate, to possible intermediate signing certificates, to the host certificate.

Secret

This field contains sensitive information that usually shouldn't be added to a config directly, read our secrets page for more info.

Type: string
Default: ""

# Examples

root_cas: |-
  -----BEGIN CERTIFICATE-----
  ...
  -----END CERTIFICATE-----

tls.root_cas_file​

An optional path of a root certificate authority file to use. This is a file, often with a .pem extension, containing a certificate chain from the parent trusted root certificate, to possible intermediate signing certificates, to the host certificate.

Type: string
Default: ""

# Examples

root_cas_file: ./root_cas.pem

tls.client_certs​

A list of client certificates to use. For each certificate either the fields cert and key, or cert_file and key_file should be specified, but not both.

Type: array
Default: []

# Examples

client_certs:
  - cert: foo
    key: bar

client_certs:
  - cert_file: ./example.pem
    key_file: ./example.key

tls.client_certs[].cert​

A plain text certificate to use.

Type: string
Default: ""

tls.client_certs[].key​

A plain text certificate key to use.

Secret

This field contains sensitive information that usually shouldn't be added to a config directly, read our secrets page for more info.

Type: string
Default: ""

tls.client_certs[].cert_file​

The path of a certificate to use.

Type: string
Default: ""

tls.client_certs[].key_file​

The path of a certificate key to use.

Type: string
Default: ""

tls.client_certs[].password​

A plain text password for when the private key is password encrypted in PKCS#1 or PKCS#8 format. The obsolete pbeWithMD5AndDES-CBC algorithm is not supported for the PKCS#8 format. Warning: Since it does not authenticate the ciphertext, it is vulnerable to padding oracle attacks that can let an attacker recover the plaintext.

Secret

This field contains sensitive information that usually shouldn't be added to a config directly, read our secrets page for more info.

Type: string
Default: ""

# Examples

password: foo

password: ${KEY_PASSWORD}

sasl​

Enables SASL authentication.

Type: object

sasl.mechanism​

The SASL authentication mechanism, if left empty SASL authentication is not used.

Type: string
Default: "none"

OptionSummary
OAUTHBEAREROAuth Bearer based authentication.
PLAINPlain text authentication. NOTE: When using plain text auth it is extremely likely that you'll also need to enable TLS.
SCRAM-SHA-256Authentication using the SCRAM-SHA-256 mechanism.
SCRAM-SHA-512Authentication using the SCRAM-SHA-512 mechanism.
noneDefault, no SASL authentication.

sasl.user​

A PLAIN username. It is recommended that you use environment variables to populate this field.

Type: string
Default: ""

# Examples

user: ${USER}

sasl.password​

A PLAIN password. It is recommended that you use environment variables to populate this field.

Secret

This field contains sensitive information that usually shouldn't be added to a config directly, read our secrets page for more info.

Type: string
Default: ""

# Examples

password: ${PASSWORD}

sasl.access_token​

A static OAUTHBEARER access token

Type: string
Default: ""

sasl.token_cache​

Instead of using a static access_token allows you to query a cache resource to fetch OAUTHBEARER tokens from

Type: string
Default: ""

sasl.token_key​

Required when using a token_cache, the key to query the cache with for tokens.

Type: string
Default: ""

topic​

The topic to publish messages to. This field supports interpolation functions.

Type: string

client_id​

An identifier for the client connection.

Type: string
Default: "bento"

target_version​

The version of the Kafka protocol to use. This limits the capabilities used by the client and should ideally match the version of your brokers. Defaults to the oldest supported stable version.

Type: string

# Examples

target_version: 2.1.0

target_version: 3.1.0

rack_id​

A rack identifier for this client.

Type: string
Default: ""

key​

The key to publish messages with. This field supports interpolation functions.

Type: string
Default: ""

partitioner​

The partitioning algorithm to use.

Type: string
Default: "fnv1a_hash"
Options: fnv1a_hash, murmur2_hash, random, round_robin, manual.

partition​

The manually-specified partition to publish messages to, relevant only when the field partitioner is set to manual. Must be able to parse as a 32-bit integer. This field supports interpolation functions.

Type: string
Default: ""

custom_topic_creation​

If enabled, topics will be created with the specified number of partitions and replication factor if they do not already exist.

Type: object

custom_topic_creation.enabled​

Whether to enable custom topic creation.

Type: bool
Default: false

custom_topic_creation.partitions​

The number of partitions to create for new topics. Leave at -1 to use the broker configured default. Must be >= 1.

Type: int
Default: -1

custom_topic_creation.replication_factor​

The replication factor to use for new topics. Leave at -1 to use the broker configured default. Must be an odd number, and less then or equal to the number of brokers.

Type: int
Default: -1

compression​

The compression algorithm to use.

Type: string
Default: "none"
Options: none, snappy, lz4, gzip, zstd.

static_headers​

An optional map of static headers that should be added to messages in addition to metadata.

Type: object

# Examples

static_headers:
  first-static-header: value-1
  second-static-header: value-2

metadata​

Specify criteria for which metadata values are sent with messages as headers.

Type: object

metadata.exclude_prefixes​

Provide a list of explicit metadata key prefixes to be excluded when adding metadata to sent messages.

Type: array
Default: []

inject_tracing_map​

EXPERIMENTAL: A Bloblang mapping used to inject an object containing tracing propagation information into outbound messages. The specification of the injected fields will match the format used by the service wide tracer.

Type: string
Requires version 1.0.0 or newer

# Examples

inject_tracing_map: meta = @.merge(this)

inject_tracing_map: root.meta.span = this

max_in_flight​

The maximum number of messages to have in flight at a given time. Increase this to improve throughput.

Type: int
Default: 64

idempotent_write​

Enable the idempotent write producer option. This requires the IDEMPOTENT_WRITE permission on CLUSTER and can be disabled if this permission is not available.

Type: bool
Default: false

ack_replicas​

Ensure that messages have been copied across all replicas before acknowledging receipt.

Type: bool
Default: false

max_msg_bytes​

The maximum size in bytes of messages sent to the target topic.

Type: int
Default: 1000000

timeout​

The maximum period of time to wait for message sends before abandoning the request and retrying.

Type: string
Default: "5s"

retry_as_batch​

When enabled forces an entire batch of messages to be retried if any individual message fails on a send, otherwise only the individual messages that failed are retried. Disabling this helps to reduce message duplicates during intermittent errors, but also makes it impossible to guarantee strict ordering of messages.

Type: bool
Default: false

batching​

Allows you to configure a batching policy.

Type: object

# Examples

batching:
  byte_size: 5000
  count: 0
  period: 1s

batching:
  count: 10
  period: 1s

batching:
  check: this.contains("END BATCH")
  count: 0
  period: 1m

batching:
  count: 10
  jitter: 0.1
  period: 10s

batching.count​

A number of messages at which the batch should be flushed. If 0 disables count based batching.

Type: int
Default: 0

batching.byte_size​

An amount of bytes at which the batch should be flushed. If 0 disables size based batching.

Type: int
Default: 0

batching.period​

A period in which an incomplete batch should be flushed regardless of its size.

Type: string
Default: ""

# Examples

period: 1s

period: 1m

period: 500ms

batching.jitter​

A non-negative factor that adds random delay to batch flush intervals, where delay is determined uniformly at random between 0 and jitter * period. For example, with period: 100ms and jitter: 0.1, each flush will be delayed by a random duration between 0-10ms.

Type: float
Default: 0

# Examples

jitter: 0.01

jitter: 0.1

jitter: 1

batching.check​

A Bloblang query that should return a boolean value indicating whether a message should end a batch.

Type: string
Default: ""

# Examples

check: this.type == "end_of_transaction"

batching.processors​

A list of processors to apply to a batch as it is flushed. This allows you to aggregate and archive the batch however you see fit. Please note that all resulting messages are flushed as a single batch, therefore splitting the batch into smaller batches using these processors is a no-op.

Type: array

# Examples

processors:
  - archive:
      format: concatenate

processors:
  - archive:
      format: lines

processors:
  - archive:
      format: json_array

max_retries​

The maximum number of retries before giving up on the request. If set to zero there is no discrete limit.

Type: int
Default: 0

backoff​

Control time intervals between retry attempts.

Type: object

backoff.initial_interval​

The initial period to wait between retry attempts.

Type: string
Default: "3s"

# Examples

initial_interval: 50ms

initial_interval: 1s

backoff.max_interval​

The maximum period to wait between retry attempts

Type: string
Default: "10s"

# Examples

max_interval: 5s

max_interval: 1m

backoff.max_elapsed_time​

The maximum overall period of time to spend on retry attempts before the request is aborted. Setting this value to a zeroed duration (such as 0s) will result in unbounded retries.

Type: string
Default: "30s"

# Examples

max_elapsed_time: 1m

max_elapsed_time: 1h