Chapter 5. Admin Client configuration properties bootstrap.controllers Type: list Default: "" Importance: high A list of host/port pairs to use for establishing the initial connection to the KRaft controller quorum. This list should be in the form host1:port1,host2:port2,... . bootstrap.servers Type: list Default: "" 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). ssl.key.password Type: password Default: null Importance: high The password of the private key in the key store file or the PEM key specified in 'ssl.keystore.key'. ssl.keystore.certificate.chain Type: password Default: null Importance: high Certificate chain in the format specified by 'ssl.keystore.type'. Default SSL engine factory supports only PEM format with a list of X.509 certificates. ssl.keystore.key Type: password Default: null Importance: high Private key in the format specified by 'ssl.keystore.type'. Default SSL engine factory supports only PEM format with PKCS#8 keys. If the key is encrypted, key password must be specified using 'ssl.key.password'. 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. Key store password is not supported for PEM format. ssl.truststore.certificates Type: password Default: null Importance: high Trusted certificates in the format specified by 'ssl.truststore.type'. Default SSL engine factory supports only PEM format with X.509 certificates. 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, trust store file configured will still be used, but integrity checking is disabled. Trust store password is not supported for PEM format. client.dns.lookup Type: string Default: use_all_dns_ips Valid Values: [use_all_dns_ips, resolve_canonical_bootstrap_servers_only] Importance: medium Controls how the client uses DNS lookups. If set to use_all_dns_ips , connect to each returned IP address in sequence until a successful connection is established. After a disconnection, the IP is used. Once all IPs have been used once, the client resolves the IP(s) from the hostname again (both the JVM and the OS cache DNS name lookups, however). If set to resolve_canonical_bootstrap_servers_only , resolve each bootstrap address into a list of canonical names. After the bootstrap phase, this behaves the same as use_all_dns_ips . client.id Type: string Default: "" Importance: medium 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. connections.max.idle.ms Type: long Default: 300000 (5 minutes) Importance: medium Close idle connections after the number of milliseconds specified by this config. default.api.timeout.ms Type: int Default: 60000 (1 minute) Valid Values: [0,... ] Importance: medium Specifies the timeout (in milliseconds) for client APIs. This configuration is used as the default timeout for all client operations that do not specify a timeout parameter. receive.buffer.bytes Type: int Default: 65536 (64 kibibytes) 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 (30 seconds) 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. sasl.oauthbearer.jwks.endpoint.url Type: string Default: null Importance: medium The OAuth/OIDC provider URL from which the provider's JWKS (JSON Web Key Set) can be retrieved. The URL can be HTTP(S)-based or file-based. If the URL is HTTP(S)-based, the JWKS data will be retrieved from the OAuth/OIDC provider via the configured URL on broker startup. All then-current keys will be cached on the broker for incoming requests. If an authentication request is received for a JWT that includes a "kid" header claim value that isn't yet in the cache, the JWKS endpoint will be queried again on demand. However, the broker polls the URL every sasl.oauthbearer.jwks.endpoint.refresh.ms milliseconds to refresh the cache with any forthcoming keys before any JWT requests that include them are received. If the URL is file-based, the broker will load the JWKS file from a configured location on startup. In the event that the JWT includes a "kid" header value that isn't in the JWKS file, the broker will reject the JWT and authentication will fail. sasl.oauthbearer.token.endpoint.url Type: string Default: null Importance: medium The URL for the OAuth/OIDC identity provider. If the URL is HTTP(S)-based, it is the issuer's token endpoint URL to which requests will be made to login based on the configuration in sasl.jaas.config. If the URL is file-based, it specifies a file containing an access token (in JWT serialized form) issued by the OAuth/OIDC identity provider to use for authorization. security.protocol Type: string Default: PLAINTEXT Valid Values: (case insensitive) [SASL_SSL, PLAINTEXT, SSL, SASL_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 (128 kibibytes) 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. socket.connection.setup.timeout.max.ms Type: long Default: 30000 (30 seconds) Importance: medium The maximum amount of time the client will wait for the socket connection to be established. The connection setup timeout will increase exponentially for each consecutive connection failure up to this maximum. To avoid connection storms, a randomization factor of 0.2 will be applied to the timeout resulting in a random range between 20% below and 20% above the computed value. socket.connection.setup.timeout.ms Type: long Default: 10000 (10 seconds) Importance: medium The amount of time the client will wait for the socket connection to be established. If the connection is not built before the timeout elapses, clients will close the socket channel. This value is the initial backoff value and will increase exponentially for each consecutive connection failure, up to the socket.connection.setup.timeout.max.ms value. ssl.enabled.protocols Type: list Default: TLSv1.2,TLSv1.3 Importance: medium The list of protocols enabled for SSL connections. The default is 'TLSv1.2,TLSv1.3' when running with Java 11 or newer, 'TLSv1.2' otherwise. With the default value for Java 11, clients and servers will prefer TLSv1.3 if both support it and fallback to TLSv1.2 otherwise (assuming both support at least TLSv1.2). This default should be fine for most cases. Also see the config documentation for ssl.protocol . ssl.keystore.type Type: string Default: JKS Importance: medium The file format of the key store file. This is optional for client. The values currently supported by the default ssl.engine.factory.class are [JKS, PKCS12, PEM]. ssl.protocol Type: string Default: TLSv1.3 Importance: medium The SSL protocol used to generate the SSLContext. The default is 'TLSv1.3' when running with Java 11 or newer, 'TLSv1.2' otherwise. This value should be fine for most use cases. Allowed values in recent JVMs are 'TLSv1.2' and 'TLSv1.3'. 'TLS', 'TLSv1.1', 'SSL', 'SSLv2' and 'SSLv3' may be supported in older JVMs, but their usage is discouraged due to known security vulnerabilities. With the default value for this config and 'ssl.enabled.protocols', clients will downgrade to 'TLSv1.2' if the server does not support 'TLSv1.3'. If this config is set to 'TLSv1.2', clients will not use 'TLSv1.3' even if it is one of the values in ssl.enabled.protocols and the server only supports 'TLSv1.3'. 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. The values currently supported by the default ssl.engine.factory.class are [JKS, PKCS12, PEM]. auto.include.jmx.reporter Type: boolean Default: true Importance: low Deprecated. Whether to automatically include JmxReporter even if it's not listed in metric.reporters . This configuration will be removed in Kafka 4.0, users should instead include org.apache.kafka.common.metrics.JmxReporter in metric.reporters in order to enable the JmxReporter. enable.metrics.push Type: boolean Default: true Importance: low Whether to enable pushing of client metrics to the cluster, if the cluster has a client metrics subscription which matches this client. metadata.max.age.ms Type: long Default: 300000 (5 minutes) 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. metadata.recovery.strategy Type: string Default: none Valid Values: (case insensitive) [REBOOTSTRAP, NONE] Importance: low Controls how the client recovers when none of the brokers known to it is available. If set to none , the client fails. If set to rebootstrap , the client repeats the bootstrap process using bootstrap.servers . Rebootstrapping is useful when a client communicates with brokers so infrequently that the set of brokers may change entirely before the client refreshes metadata. Metadata recovery is triggered when all last-known brokers appear unavailable simultaneously. Brokers appear unavailable when disconnected and no current retry attempt is in-progress. Consider increasing reconnect.backoff.ms and reconnect.backoff.max.ms and decreasing socket.connection.setup.timeout.ms and socket.connection.setup.timeout.max.ms for the client. metric.reporters Type: list Default: "" 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, TRACE] Importance: low The highest recording level for metrics. metrics.sample.window.ms Type: long Default: 30000 (30 seconds) Valid Values: [0,... ] Importance: low The window of time a metrics sample is computed over. reconnect.backoff.max.ms Type: long Default: 1000 (1 second) 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. This value is the initial backoff value and will increase exponentially for each consecutive connection failure, up to the reconnect.backoff.max.ms value. retries Type: int Default: 2147483647 Valid Values: [0,... ,2147483647] Importance: low Setting a value greater than zero will cause the client to resend any request that fails with a potentially transient error. It is recommended to set the value to either zero or MAX_VALUE and use corresponding timeout parameters to control how long a client should retry a request. retry.backoff.max.ms Type: long Default: 1000 (1 second) Valid Values: [0,... ] Importance: low The maximum amount of time in milliseconds to wait when retrying a request to the broker that has repeatedly failed. If provided, the backoff per client will increase exponentially for each failed request, up to this maximum. To prevent all clients from being synchronized upon retry, a randomized jitter with a factor of 0.2 will be applied to the backoff, resulting in the backoff falling within a range between 20% below and 20% above the computed value. If retry.backoff.ms is set to be higher than retry.backoff.max.ms , then retry.backoff.max.ms will be used as a constant backoff from the beginning without any exponential increase. 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. This value is the initial backoff value and will increase exponentially for each failed request, up to the retry.backoff.max.ms value. 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.connect.timeout.ms Type: int Default: null Importance: low The (optional) value in milliseconds for the external authentication provider connection timeout. Currently applies only to OAUTHBEARER. sasl.login.read.timeout.ms Type: int Default: null Importance: low The (optional) value in milliseconds for the external authentication provider read timeout. Currently applies only to OAUTHBEARER. 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. sasl.login.retry.backoff.max.ms Type: long Default: 10000 (10 seconds) Importance: low The (optional) value in milliseconds for the maximum wait between login attempts to the external authentication provider. Login uses an exponential backoff algorithm with an initial wait based on the sasl.login.retry.backoff.ms setting and will double in wait length between attempts up to a maximum wait length specified by the sasl.login.retry.backoff.max.ms setting. Currently applies only to OAUTHBEARER. sasl.login.retry.backoff.ms Type: long Default: 100 Importance: low The (optional) value in milliseconds for the initial wait between login attempts to the external authentication provider. Login uses an exponential backoff algorithm with an initial wait based on the sasl.login.retry.backoff.ms setting and will double in wait length between attempts up to a maximum wait length specified by the sasl.login.retry.backoff.max.ms setting. Currently applies only to OAUTHBEARER. sasl.oauthbearer.clock.skew.seconds Type: int Default: 30 Importance: low The (optional) value in seconds to allow for differences between the time of the OAuth/OIDC identity provider and the broker. sasl.oauthbearer.expected.audience Type: list Default: null Importance: low The (optional) comma-delimited setting for the broker to use to verify that the JWT was issued for one of the expected audiences. The JWT will be inspected for the standard OAuth "aud" claim and if this value is set, the broker will match the value from JWT's "aud" claim to see if there is an exact match. If there is no match, the broker will reject the JWT and authentication will fail. sasl.oauthbearer.expected.issuer Type: string Default: null Importance: low The (optional) setting for the broker to use to verify that the JWT was created by the expected issuer. The JWT will be inspected for the standard OAuth "iss" claim and if this value is set, the broker will match it exactly against what is in the JWT's "iss" claim. If there is no match, the broker will reject the JWT and authentication will fail. sasl.oauthbearer.jwks.endpoint.refresh.ms Type: long Default: 3600000 (1 hour) Importance: low The (optional) value in milliseconds for the broker to wait between refreshing its JWKS (JSON Web Key Set) cache that contains the keys to verify the signature of the JWT. sasl.oauthbearer.jwks.endpoint.retry.backoff.max.ms Type: long Default: 10000 (10 seconds) Importance: low The (optional) value in milliseconds for the maximum wait between attempts to retrieve the JWKS (JSON Web Key Set) from the external authentication provider. JWKS retrieval uses an exponential backoff algorithm with an initial wait based on the sasl.oauthbearer.jwks.endpoint.retry.backoff.ms setting and will double in wait length between attempts up to a maximum wait length specified by the sasl.oauthbearer.jwks.endpoint.retry.backoff.max.ms setting. sasl.oauthbearer.jwks.endpoint.retry.backoff.ms Type: long Default: 100 Importance: low The (optional) value in milliseconds for the initial wait between JWKS (JSON Web Key Set) retrieval attempts from the external authentication provider. JWKS retrieval uses an exponential backoff algorithm with an initial wait based on the sasl.oauthbearer.jwks.endpoint.retry.backoff.ms setting and will double in wait length between attempts up to a maximum wait length specified by the sasl.oauthbearer.jwks.endpoint.retry.backoff.max.ms setting. sasl.oauthbearer.scope.claim.name Type: string Default: scope Importance: low The OAuth claim for the scope is often named "scope", but this (optional) setting can provide a different name to use for the scope included in the JWT payload's claims if the OAuth/OIDC provider uses a different name for that claim. sasl.oauthbearer.sub.claim.name Type: string Default: sub Importance: low The OAuth claim for the subject is often named "sub", but this (optional) setting can provide a different name to use for the subject included in the JWT payload's claims if the OAuth/OIDC provider uses a different name for that claim. security.providers Type: string Default: null Importance: low A list of configurable creator classes each returning a provider implementing security algorithms. These classes should implement the org.apache.kafka.common.security.auth.SecurityProviderCreator interface. 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.engine.factory.class Type: class Default: null Importance: low The class of type org.apache.kafka.common.security.auth.SslEngineFactory to provide SSLEngine objects. Default value is org.apache.kafka.common.security.ssl.DefaultSslEngineFactory. Alternatively, setting this to org.apache.kafka.common.security.ssl.CommonNameLoggingSslEngineFactory will log the common name of expired SSL certificates used by clients to authenticate at any of the brokers with log level INFO. Note that this will cause a tiny delay during establishment of new connections from mTLS clients to brokers due to the extra code for examining the certificate chain provided by the client. Note further that the implementation uses a custom truststore based on the standard Java truststore and thus might be considered a security risk due to not being as mature as the standard one. 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.

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