Appendix C. Consumer configuration parameters

key.deserializer

Type: class
Importance: high

Deserializer class for key that implements the org.apache.kafka.common.serialization.Deserializer interface.

value.deserializer

Type: class
Importance: high

Deserializer class for value that implements the org.apache.kafka.common.serialization.Deserializer interface.

bootstrap.servers

Type: list
Default: ""
Valid Values: non-null value
Importance: high

A list of host/port pairs to use for establishing the initial connection to the Kafka cluster. The client will make use of all servers irrespective of which servers are specified here for bootstrapping—this list only impacts the initial hosts used to discover the full set of servers. This list should be in the form host1:port1,host2:port2,…​. Since these servers are just used for the initial connection to discover the full cluster membership (which may change dynamically), this list need not contain the full set of servers (you may want more than one, though, in case a server is down).

fetch.min.bytes

Type: int
Default: 1
Valid Values: [0,…​]
Importance: high

The minimum amount of data the server should return for a fetch request. If insufficient data is available the request will wait for that much data to accumulate before answering the request. The default setting of 1 byte means that fetch requests are answered as soon as a single byte of data is available or the fetch request times out waiting for data to arrive. Setting this to something greater than 1 will cause the server to wait for larger amounts of data to accumulate which can improve server throughput a bit at the cost of some additional latency.

group.id

Type: string
Default: ""
Importance: high

A unique string that identifies the consumer group this consumer belongs to. This property is required if the consumer uses either the group management functionality by using subscribe(topic) or the Kafka-based offset management strategy.

heartbeat.interval.ms

Type: int
Default: 3000
Importance: high

The expected time between heartbeats to the consumer coordinator when using Kafka’s group management facilities. Heartbeats are used to ensure that the consumer’s session stays active and to facilitate rebalancing when new consumers join or leave the group. The value must be set lower than session.timeout.ms, but typically should be set no higher than 1/3 of that value. It can be adjusted even lower to control the expected time for normal rebalances.

max.partition.fetch.bytes

Type: int
Default: 1048576
Valid Values: [0,…​]
Importance: high

The maximum amount of data per-partition the server will return. Records are fetched in batches by the consumer. If the first record batch in the first non-empty partition of the fetch is larger than this limit, the batch will still be returned to ensure that the consumer can make progress. The maximum record batch size accepted by the broker is defined via message.max.bytes (broker config) or max.message.bytes (topic config). See fetch.max.bytes for limiting the consumer request size.

session.timeout.ms

Type: int
Default: 10000
Importance: high

The timeout used to detect consumer failures when using Kafka’s group management facility. The consumer sends periodic heartbeats to indicate its liveness to the broker. If no heartbeats are received by the broker before the expiration of this session timeout, then the broker will remove this consumer from the group and initiate a rebalance. Note that the value must be in the allowable range as configured in the broker configuration by group.min.session.timeout.ms and group.max.session.timeout.ms.

ssl.key.password

Type: password
Default: null
Importance: high

The password of the private key in the key store file. This is optional for client.

ssl.keystore.location

Type: string
Default: null
Importance: high

The location of the key store file. This is optional for client and can be used for two-way authentication for client.

ssl.keystore.password

Type: password
Default: null
Importance: high

The store password for the key store file. This is optional for client and only needed if ssl.keystore.location is configured.

ssl.truststore.location

Type: string
Default: null
Importance: high

The location of the trust store file.

ssl.truststore.password

Type: password
Default: null
Importance: high

The password for the trust store file. If a password is not set access to the truststore is still available, but integrity checking is disabled.

auto.offset.reset

Type: string
Default: latest
Valid Values: [latest, earliest, none]
Importance: medium

What to do when there is no initial offset in Kafka or if the current offset does not exist any more on the server (e.g. because that data has been deleted):

  • earliest: automatically reset the offset to the earliest offset
  • latest: automatically reset the offset to the latest offset
  • none: throw exception to the consumer if no previous offset is found for the consumer’s group
  • anything else: throw exception to the consumer.
connections.max.idle.ms

Type: long
Default: 540000
Importance: medium

Close idle connections after the number of milliseconds specified by this config.

default.api.timeout.ms

Type: int
Default: 60000
Valid Values: [0,…​]
Importance: medium

Specifies the timeout (in milliseconds) for consumer APIs that could block. This configuration is used as the default timeout for all consumer operations that do not explicitly accept a timeout parameter.

enable.auto.commit

Type: boolean
Default: true
Importance: medium

If true the consumer’s offset will be periodically committed in the background.

exclude.internal.topics

Type: boolean
Default: true
Importance: medium

Whether records from internal topics (such as offsets) should be exposed to the consumer. If set to true the only way to receive records from an internal topic is subscribing to it.

fetch.max.bytes

Type: int
Default: 52428800
Valid Values: [0,…​]
Importance: medium

The maximum amount of data the server should return for a fetch request. Records are fetched in batches by the consumer, and if the first record batch in the first non-empty partition of the fetch is larger than this value, the record batch will still be returned to ensure that the consumer can make progress. As such, this is not a absolute maximum. The maximum record batch size accepted by the broker is defined via message.max.bytes (broker config) or max.message.bytes (topic config). Note that the consumer performs multiple fetches in parallel.

isolation.level

Type: string
Default: read_uncommitted
Valid Values: [read_committed, read_uncommitted]
Importance: medium

Controls how to read messages written transactionally. If set to read_committed, consumer.poll() will only return transactional messages which have been committed. If set to `read_uncommitted’ (the default), consumer.poll() will return all messages, even transactional messages which have been aborted. Non-transactional messages will be returned unconditionally in either mode.

Messages will always be returned in offset order. Hence, in read_committed mode, consumer.poll() will only return messages up to the last stable offset (LSO), which is the one less than the offset of the first open transaction. In particular any messages appearing after messages belonging to ongoing transactions will be withheld until the relevant transaction has been completed. As a result, read_committed consumers will not be able to read up to the high watermark when there are in flight transactions.

Further, when in `read_committed</mode> the seekToEnd method will return the LSO.
max.poll.interval.ms

Type: int
Default: 300000
Valid Values: [1,…​]
Importance: medium

The maximum delay between invocations of poll() when using consumer group management. This places an upper bound on the amount of time that the consumer can be idle before fetching more records. If poll() is not called before expiration of this timeout, then the consumer is considered failed and the group will rebalance in order to reassign the partitions to another member.

max.poll.records

Type: int
Default: 500
Valid Values: [1,…​]
Importance: medium

The maximum number of records returned in a single call to poll().

partition.assignment.strategy

Type: list
Default: class org.apache.kafka.clients.consumer.RangeAssignor
Valid Values: non-null value
Importance: medium

The class name of the partition assignment strategy that the client will use to distribute partition ownership amongst consumer instances when group management is used.

receive.buffer.bytes

Type: int
Default: 65536
Valid Values: [-1,…​]
Importance: medium

The size of the TCP receive buffer (SO_RCVBUF) to use when reading data. If the value is -1, the OS default will be used.

request.timeout.ms

Type: int
Default: 30000
Valid Values: [0,…​]
Importance: medium

The configuration controls the maximum amount of time the client will wait for the response of a request. If the response is not received before the timeout elapses the client will resend the request if necessary or fail the request if retries are exhausted.

sasl.client.callback.handler.class

Type: class
Default: null
Importance: medium

The fully qualified name of a SASL client callback handler class that implements the AuthenticateCallbackHandler interface.

sasl.jaas.config

Type: password
Default: null
Importance: medium

JAAS login context parameters for SASL connections in the format used by JAAS configuration files. JAAS configuration file format is described here. The format for the value is: ‘loginModuleClass controlFlag (optionName=optionValue)*;’. For brokers, the config must be prefixed with listener prefix and SASL mechanism name in lower-case. For example, listener.name.sasl_ssl.scram-sha-256.sasl.jaas.config=com.example.ScramLoginModule required;.

sasl.kerberos.service.name

Type: string
Default: null
Importance: medium

The Kerberos principal name that Kafka runs as. This can be defined either in Kafka’s JAAS config or in Kafka’s config.

sasl.login.callback.handler.class

Type: class
Default: null
Importance: medium

The fully qualified name of a SASL login callback handler class that implements the AuthenticateCallbackHandler interface. For brokers, login callback handler config must be prefixed with listener prefix and SASL mechanism name in lower-case. For example, listener.name.sasl_ssl.scram-sha-256.sasl.login.callback.handler.class=com.example.CustomScramLoginCallbackHandler.

sasl.login.class

Type: class
Default: null
Importance: medium

The fully qualified name of a class that implements the Login interface. For brokers, login config must be prefixed with listener prefix and SASL mechanism name in lower-case. For example, listener.name.sasl_ssl.scram-sha-256.sasl.login.class=com.example.CustomScramLogin.

sasl.mechanism

Type: string
Default: GSSAPI
Importance: medium

SASL mechanism used for client connections. This may be any mechanism for which a security provider is available. GSSAPI is the default mechanism.

security.protocol

Type: string
Default: PLAINTEXT
Importance: medium

Protocol used to communicate with brokers. Valid values are: PLAINTEXT, SSL, SASL_PLAINTEXT, SASL_SSL.

send.buffer.bytes

Type: int
Default: 131072
Valid Values: [-1,…​]
Importance: medium

The size of the TCP send buffer (SO_SNDBUF) to use when sending data. If the value is -1, the OS default will be used.

ssl.enabled.protocols

Type: list
Default: TLSv1.2,TLSv1.1,TLSv1
Importance: medium

The list of protocols enabled for SSL connections.

ssl.keystore.type

Type: string
Default: JKS
Importance: medium

The file format of the key store file. This is optional for client.

ssl.protocol

Type: string
Default: TLS
Importance: medium

The SSL protocol used to generate the SSLContext. Default setting is TLS, which is fine for most cases. Allowed values in recent JVMs are TLS, TLSv1.1 and TLSv1.2. SSL, SSLv2 and SSLv3 may be supported in older JVMs, but their usage is discouraged due to known security vulnerabilities.

ssl.provider

Type: string
Default: null
Importance: medium

The name of the security provider used for SSL connections. Default value is the default security provider of the JVM.

ssl.truststore.type

Type: string
Default: JKS
Importance: medium

The file format of the trust store file.

auto.commit.interval.ms

Type: int
Default: 5000
Valid Values: [0,…​]
Importance: low

The frequency in milliseconds that the consumer offsets are auto-committed to Kafka if enable.auto.commit is set to true.

check.crcs

Type: boolean
Default: true
Importance: low

Automatically check the CRC32 of the records consumed. This ensures no on-the-wire or on-disk corruption to the messages occurred. This check adds some overhead, so it may be disabled in cases seeking extreme performance.

client.id

Type: string
Default: ""
Importance: low

An id string to pass to the server when making requests. The purpose of this is to be able to track the source of requests beyond just ip/port by allowing a logical application name to be included in server-side request logging.

fetch.max.wait.ms

Type: int
Default: 500
Valid Values: [0,…​]
Importance: low

The maximum amount of time the server will block before answering the fetch request if there isn’t sufficient data to immediately satisfy the requirement given by fetch.min.bytes.

interceptor.classes

Type: list
Default: ""
Valid Values: non-null value
Importance: low

A list of classes to use as interceptors. Implementing the org.apache.kafka.clients.consumer.ConsumerInterceptor interface allows you to intercept (and possibly mutate) records received by the consumer. By default, there are no interceptors.

metadata.max.age.ms

Type: long
Default: 300000
Valid Values: [0,…​]
Importance: low

The period of time in milliseconds after which we force a refresh of metadata even if we haven’t seen any partition leadership changes to proactively discover any new brokers or partitions.

metric.reporters

Type: list
Default: ""
Valid Values: non-null value
Importance: low

A list of classes to use as metrics reporters. Implementing the org.apache.kafka.common.metrics.MetricsReporter interface allows plugging in classes that will be notified of new metric creation. The JmxReporter is always included to register JMX statistics.

metrics.num.samples

Type: int
Default: 2
Valid Values: [1,…​]
Importance: low

The number of samples maintained to compute metrics.

metrics.recording.level

Type: string
Default: INFO
Valid Values: [INFO, DEBUG]
Importance: low

The highest recording level for metrics.

metrics.sample.window.ms

Type: long
Default: 30000
Valid Values: [0,…​]
Importance: low

The window of time a metrics sample is computed over.

reconnect.backoff.max.ms

Type: long
Default: 1000
Valid Values: [0,…​]
Importance: low

The maximum amount of time in milliseconds to wait when reconnecting to a broker that has repeatedly failed to connect. If provided, the backoff per host will increase exponentially for each consecutive connection failure, up to this maximum. After calculating the backoff increase, 20% random jitter is added to avoid connection storms.

reconnect.backoff.ms

Type: long
Default: 50
Valid Values: [0,…​]
Importance: low

The base amount of time to wait before attempting to reconnect to a given host. This avoids repeatedly connecting to a host in a tight loop. This backoff applies to all connection attempts by the client to a broker.

retry.backoff.ms

Type: long
Default: 100
Valid Values: [0,…​]
Importance: low

The amount of time to wait before attempting to retry a failed request to a given topic partition. This avoids repeatedly sending requests in a tight loop under some failure scenarios.

sasl.kerberos.kinit.cmd

Type: string
Default: /usr/bin/kinit
Importance: low

Kerberos kinit command path.

sasl.kerberos.min.time.before.relogin

Type: long
Default: 60000
Importance: low

Login thread sleep time between refresh attempts.

sasl.kerberos.ticket.renew.jitter

Type: double
Default: 0.05
Importance: low

Percentage of random jitter added to the renewal time.

sasl.kerberos.ticket.renew.window.factor

Type: double
Default: 0.8
Importance: low

Login thread will sleep until the specified window factor of time from last refresh to ticket’s expiry has been reached, at which time it will try to renew the ticket.

sasl.login.refresh.buffer.seconds

Type: short
Default: 300
Valid Values: [0,…​,3600]
Importance: low

The amount of buffer time before credential expiration to maintain when refreshing a credential, in seconds. If a refresh would otherwise occur closer to expiration than the number of buffer seconds then the refresh will be moved up to maintain as much of the buffer time as possible. Legal values are between 0 and 3600 (1 hour); a default value of 300 (5 minutes) is used if no value is specified. This value and sasl.login.refresh.min.period.seconds are both ignored if their sum exceeds the remaining lifetime of a credential. Currently applies only to OAUTHBEARER.

sasl.login.refresh.min.period.seconds

Type: short
Default: 60
Valid Values: [0,…​,900]
Importance: low

The desired minimum time for the login refresh thread to wait before refreshing a credential, in seconds. Legal values are between 0 and 900 (15 minutes); a default value of 60 (1 minute) is used if no value is specified. This value and sasl.login.refresh.buffer.seconds are both ignored if their sum exceeds the remaining lifetime of a credential. Currently applies only to OAUTHBEARER.

sasl.login.refresh.window.factor

Type: double
Default: 0.8
Valid Values: [0.5,…​,1.0]
Importance: low

Login refresh thread will sleep until the specified window factor relative to the credential’s lifetime has been reached, at which time it will try to refresh the credential. Legal values are between 0.5 (50%) and 1.0 (100%) inclusive; a default value of 0.8 (80%) is used if no value is specified. Currently applies only to OAUTHBEARER.

sasl.login.refresh.window.jitter

Type: double
Default: 0.05
Valid Values: [0.0,…​,0.25]
Importance: low

The maximum amount of random jitter relative to the credential’s lifetime that is added to the login refresh thread’s sleep time. Legal values are between 0 and 0.25 (25%) inclusive; a default value of 0.05 (5%) is used if no value is specified. Currently applies only to OAUTHBEARER.

ssl.cipher.suites

Type: list
Default: null
Importance: low

A list of cipher suites. This is a named combination of authentication, encryption, MAC and key exchange algorithm used to negotiate the security settings for a network connection using TLS or SSL network protocol. By default all the available cipher suites are supported.

ssl.endpoint.identification.algorithm

Type: string
Default: https
Importance: low

The endpoint identification algorithm to validate server hostname using server certificate.

ssl.keymanager.algorithm

Type: string
Default: SunX509
Importance: low

The algorithm used by key manager factory for SSL connections. Default value is the key manager factory algorithm configured for the Java Virtual Machine.

ssl.secure.random.implementation

Type: string
Default: null
Importance: low

The SecureRandom PRNG implementation to use for SSL cryptography operations.

ssl.trustmanager.algorithm

Type: string
Default: PKIX
Importance: low

The algorithm used by trust manager factory for SSL connections. Default value is the trust manager factory algorithm configured for the Java Virtual Machine.