config/consumer.properties

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# this work for additional information regarding copyright ownership.
# The ASF licenses this file to You under the Apache License, Version 2.0
# (the "License"); you may not use this file except in compliance with
# the License.  You may obtain a copy of the License at
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#    http://www.apache.org/licenses/LICENSE-2.0
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# Unless required by applicable law or agreed to in writing, software
# distributed under the License is distributed on an "AS IS" BASIS,
# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
# See the License for the specific language governing permissions and
# limitations under the License.

# See org.apache.kafka.clients.consumer.ConsumerConfig for more details.
# Consider using environment variables or external configuration management
# for sensitive information like passwords and environment-specific settings.

##################### Consumer Basics #######################

# List of Kafka brokers used for initial cluster discovery and metadata retrieval.
# Format: host1:port1,host2:port2,host3:port3
# Include all brokers for high availability
bootstrap.servers=localhost:9092

# Client identifier for logging and metrics.
# Helps with debugging and monitoring.
client.id=test-consumer

##################### Transaction Support #####################

# Isolation level for reading messages.
# Options: read_uncommitted (default), read_committed (for exactly-once semantics).
isolation.level=read_uncommitted

##################### Consumer Group Configuration #####################

# Unique identifier for this consumer group.
# All consumers with the same group.id will share partition consumption.
group.id=test-consumer-group

# What to do when there is no initial offset or if the current offset no longer exists.
# Options: earliest (from beginning), latest (from end), none (throw exception).
# Use 'earliest' to avoid data loss on first run.
auto.offset.reset=earliest

##################### Partition Assignment Strategy #####################

# Strategy for assigning partitions to consumers in a group.
# Options: RangeAssignor, RoundRobinAssignor, StickyAssignor, CooperativeStickyAssignor.
# CooperativeStickyAssignor is recommended (requires Kafka 2.4+).
partition.assignment.strategy=org.apache.kafka.clients.consumer.CooperativeStickyAssignor

##################### Deserialization #####################

# Deserializer class for message keys.
# Common options: StringDeserializer, ByteArrayDeserializer, AvroDeserializer.
key.deserializer=org.apache.kafka.common.serialization.StringDeserializer

# Deserializer class for message values.
value.deserializer=org.apache.kafka.common.serialization.StringDeserializer

##################### Offset Management #####################

# Whether to automatically commit offsets in the background.
# Set to false for manual offset management and exactly-once processing.
enable.auto.commit=true

# Frequency (in milliseconds) at which offsets are auto-committed.
# Lower values provide better fault tolerance but increase broker load.
auto.commit.interval.ms=5000

##################### Classic Group Session Management #####################

# Timeout for detecting consumer failures when using group management.
# Must be between group.min.session.timeout.ms and group.max.session.timeout.ms (broker config).
session.timeout.ms=30000

# Expected time between heartbeats when using group management.
# Should be lower than session.timeout.ms (typically 1/3 of session timeout).
heartbeat.interval.ms=10000

# Maximum time between successive calls to poll().
# If exceeded, consumer is considered failed and partition rebalancing occurs.
max.poll.interval.ms=300000

##################### Retry And Error Handling #####################

# Initial and max time to wait for failed request retries.
# The retry.backoff.ms is the initial backoff value and will increase exponentially
# for each failed request, up to the retry.backoff.max.ms value.
retry.backoff.ms=100
retry.backoff.max.ms=1000

# Total time to wait for a response to a request.
request.timeout.ms=40000

# Close idle connections after this many milliseconds.
connections.max.idle.ms=540000

##################### Security Configuration #####################

# Security protocol for communication with brokers.
# Options: PLAINTEXT, SSL, SASL_PLAINTEXT, SASL_SSL
#security.protocol=SASL_SSL

# SSL configuration.
#ssl.truststore.location=/path/to/truststore.jks
#ssl.truststore.password=truststore-password

# SASL configuration.
#sasl.mechanism=PLAIN
#sasl.jaas.config=org.apache.kafka.common.security.plain.PlainLoginModule required \
#    username="your-username" \
#    password="your-password";

##################### Performance And Throughput #####################

# Minimum data size (bytes) and maximum polling timeout (ms).
# Whichever condition is met first will trigger the fetch operation.
# Balances response latency against message batching efficiency.
# For remote partition fetching, configure remote.fetch.max.wait.ms instead.
fetch.min.bytes=1
fetch.max.wait.ms=500

# Set soft limits to the amount of bytes per fetch request and partition.
# Both max.partition.fetch.bytes and fetch.max.bytes limits can be exceeded when
# the first batch in the first non-empty partition is larger than the configured
# value to ensure that the consumer can make progress.
# Configuring message.max.bytes (broker config) or max.message.bytes (topic config)
# <= fetch.max.bytes prevents oversized fetch responses.
fetch.max.bytes=52428800
max.partition.fetch.bytes=1048576

# Maximum number of records returned in a single poll() call.
# Higher values increase throughput but may cause longer processing delays.
max.poll.records=500