kafka

Connects to Kafka brokers and consumes one or more topics.

Common

# Common config fields, showing default values
input:
  label: ""
  kafka:
    addresses: [] # No default (required)
    topics: [] # No default (required)
    target_version: 2.1.0 # No default (optional)
    consumer_group: ""
    checkpoint_limit: 1024
    auto_replay_nacks: true

Advanced

# Advanced config fields, showing default values
input:
  label: ""
  kafka:
    addresses: [] # No default (required)
    topics: [] # No default (required)
    target_version: 2.1.0 # No default (optional)
    tls:
      enabled: false
      skip_cert_verify: false
      enable_renegotiation: false
      root_cas: ""
      root_cas_file: ""
      client_certs: []
    sasl:
      mechanism: none
      user: ""
      password: ""
      access_token: ""
      token_cache: ""
      token_key: ""
    consumer_group: ""
    client_id: benthos
    rack_id: ""
    start_from_oldest: true
    checkpoint_limit: 1024
    auto_replay_nacks: true
    commit_period: 1s
    max_processing_period: 100ms
    extract_tracing_map: root = @ # No default (optional)
    group:
      session_timeout: 10s
      heartbeat_interval: 3s
      rebalance_timeout: 60s
    fetch_buffer_cap: 256
    multi_header: false
    batching:
      count: 0
      byte_size: 0
      period: ""
      check: ""
      processors: [] # No default (optional)

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, and messages of the same topic partition are processed with a maximum parallelism determined by the field checkpoint_limit.

In order to enforce ordered processing of partition messages set the checkpoint_limit to 1 and this will force partitions to be processed in lock-step, where a message will only be processed once the prior message is delivered.

Batching messages before processing can be enabled using the batching field, and this batching is performed per-partition such that messages of a batch will always originate from the same partition. This batching mechanism is capable of creating batches of greater size than the checkpoint_limit, in which case the next batch will only be created upon delivery of the current one.

Metadata

This input adds the following metadata fields to each message:

• kafka_key
• kafka_topic
• kafka_partition
• kafka_offset
• kafka_lag
• kafka_timestamp_unix
• kafka_tombstone_message
• 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.

Ordering

By default messages of a topic partition can be processed in parallel, up to a limit determined by the field checkpoint_limit. However, if strict ordered processing is required then this value must be set to 1 in order to process shard messages in lock-step. When doing so it is recommended that you perform batching at this component for performance as it will not be possible to batch lock-stepped messages at the output level.

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

# 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

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. Defaults to the oldest supported stable version.

Type: string

# Examples

target_version: 2.1.0

target_version: 3.1.0

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.

Sensitive Information

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.

Sensitive Information

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.

Because the obsolete pbeWithMD5AndDES-CBC algorithm does not authenticate the ciphertext, it is vulnerable to padding oracle attacks that can let an attacker recover the plaintext.

Sensitive Information

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"

Option	Summary
OAUTHBEARER	OAuth Bearer based authentication.
PLAIN	Plain text authentication. NOTE: When using plain text auth it is extremely likely that you’ll also need to enable TLS.
SCRAM-SHA-256	Authentication using the SCRAM-SHA-256 mechanism.
SCRAM-SHA-512	Authentication using the SCRAM-SHA-512 mechanism.
none	Default, 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.

Sensitive Information

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: ""

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: ""

client_id

An identifier for the client connection.

Type: string

Default: "benthos"

rack_id

A rack identifier for this client.

Type: string

Default: ""

start_from_oldest

Determines whether to consume from the oldest available offset, otherwise messages are consumed from the latest offset. The setting is applied when creating a new consumer group or the saved offset no longer exists.

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: 1024 Requires version 3.33.0 or newer

auto_replay_nacks

Whether messages that are rejected (nacked) at the output level should be automatically replayed indefinitely, eventually resulting in back pressure if the cause of the rejections is persistent. If set to false these messages will instead be deleted. Disabling auto replays can greatly improve memory efficiency of high throughput streams as the original shape of the data can be discarded immediately upon consumption and mutation.

Type: bool

Default: true

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

Requires version 3.45.0 or newer

# Examples

extract_tracing_map: root = @

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

multi_header

Decode headers into lists to allow handling of multiple values with the same key

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

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

# Examples

processors:
  - archive:
      format: concatenate

processors:
  - archive:
      format: lines

processors:
  - archive:
      format: json_array