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kafka

Connects to Kafka brokers and consumes one or more topics.

# Common config fields, showing default values
input:
  label: ""
  kafka:
    addresses:
      - localhost:9092
    topics: []
    target_version: 1.0.0
    consumer_group: benthos_consumer_group
    client_id: benthos_kafka_input
    checkpoint_limit: 1

Offsets are managed within Kafka under the specified consumer group, and partitions for each topic are automatically balanced across members of the consumer group.

The Kafka input allows parallel processing of messages from different topic partitions, but by default messages of the same topic partition are processed in lockstep in order to enforce ordered processing. This protection often means that batching messages at the output level can stall, in which case it can be tuned by increasing the field checkpoint_limit, ideally to a value greater than the number of messages you expect to batch.

Alternatively, if you perform batching at the input level using the batching field it is done per-partition and therefore avoids stalling.

Metadata​

This input adds the following metadata fields to each message:

- kafka_key
- kafka_topic
- kafka_partition
- kafka_offset
- kafka_lag
- kafka_timestamp_unix
- All existing message headers (version 0.11+)

The field kafka_lag is the calculated difference between the high water mark offset of the partition at the time of ingestion and the current message offset.

You can access these metadata fields using function interpolation.

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 input.

  • 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.

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
Default: ["localhost:9092"] 

# Examples


addresses:
  - localhost:9092


addresses:
  - localhost:9041,localhost:9042


addresses:
  - localhost:9041
  - localhost:9042

topics​

A list of topics to consume from. Multiple comma separated topics can be listed in a single element. Partitions are automatically distributed across consumers of a topic. Alternatively, it's possible to specify explicit partitions to consume from with a colon after the topic name, e.g. foo:0 would consume the partition 0 of the topic foo. This syntax supports ranges, e.g. foo:0-10 would consume partitions 0 through to 10 inclusive.

Type: array
Default: []
Requires version 3.33.0 or newer 

# Examples


topics:
  - foo
  - bar


topics:
  - foo,bar


topics:
  - foo:0
  - bar:1
  - bar:3


topics:
  - foo:0,bar:1,bar:3


topics:
  - foo:0-5

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.

Type: string
Default: "1.0.0"

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 3.45.0 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.

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.

Type: string
Default: ""

tls.client_certs[].cert_file​

The path to a certificate to use.

Type: string
Default: ""

tls.client_certs[].key_file​

The path of a certificate key to use.

Type: string
Default: ""

sasl​

Enables SASL authentication.

Type: object

sasl.mechanism​

The SASL authentication mechanism, if left empty SASL authentication is not used. Warning: SCRAM based methods within Benthos have not received a security audit.

Type: string
Default: ""

OptionSummary
PLAINPlain text authentication. NOTE: When using plain text auth it is extremely likely that you'll also need to enable TLS.
OAUTHBEAREROAuth Bearer based authentication.
SCRAM-SHA-256Authentication using the SCRAM-SHA-256 mechanism.
SCRAM-SHA-512Authentication using the SCRAM-SHA-512 mechanism.

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.

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: ""

consumer_group​

An identifier for the consumer group of the connection. This field can be explicitly made empty in order to disable stored offsets for the consumed topic partitions.

Type: string
Default: "benthos_consumer_group"

client_id​

An identifier for the client connection.

Type: string
Default: "benthos_kafka_input"

rack_id​

A rack identifier for this client.

Type: string
Default: ""

start_from_oldest​

If an offset is not found for a topic partition, determines whether to consume from the oldest available offset, otherwise messages are consumed from the latest offset.

Type: bool
Default: true

checkpoint_limit​

The maximum number of messages of the same topic and partition that can be processed at a given time. Increasing this limit enables parallel processing and batching at the output level to work on individual partitions. Any given offset will not be committed unless all messages under that offset are delivered in order to preserve at least once delivery guarantees.

Type: int
Default: 1
Requires version 3.33.0 or newer

commit_period​

The period of time between each commit of the current partition offsets. Offsets are always committed during shutdown.

Type: string
Default: "1s"

max_processing_period​

A maximum estimate for the time taken to process a message, this is used for tuning consumer group synchronization.

Type: string
Default: "100ms"

extract_tracing_map​

EXPERIMENTAL: A Bloblang mapping that attempts to extract an object containing tracing propagation information, which will then be used as the root tracing span for the message. The specification of the extracted fields must match the format used by the service wide tracer.

Type: string
Default: ""
Requires version 3.45.0 or newer 

# Examples


extract_tracing_map: root = meta()


extract_tracing_map: root = this.meta.span

group​

Tuning parameters for consumer group synchronization.

Type: object

group.session_timeout​

A period after which a consumer of the group is kicked after no heartbeats.

Type: string
Default: "10s"

group.heartbeat_interval​

A period in which heartbeats should be sent out.

Type: string
Default: "3s"

group.rebalance_timeout​

A period after which rebalancing is abandoned if unresolved.

Type: string
Default: "60s"

fetch_buffer_cap​

The maximum number of unprocessed messages to fetch at a given time.

Type: int
Default: 256

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​

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.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
Default: [] 

# Examples


processors:
  - archive:
      format: lines


processors:
  - archive:
      format: json_array


processors:
  - merge_json: {}