Kafka Usage

LogScale uses Apache Kafka internally for queuing incoming messages and for storing shared state when running LogScale in a cluster setup. This page describes how LogScale uses Kafka. If you already understand Kafka concepts, you can skip this and go to the instructions on how to install Kafka, further down this page.

For more information on Kafka configuration and settings, see Kafka Configuration.

How LogScale Uses Kafka

LogScale creates the following queues in Kafka:

You can set the environment variable HUMIO_KAFKA_TOPIC_PREFIX to add that prefix to the topic names in Kafka. Adding a prefix is recommended if you share the Kafka installation with applications other than LogScale, or with another LogScale instance. The default is not to add a prefix.

LogScale configures default retention settings on the topics when it creates them. If they exist already, LogScale does not alter retention settings on the topics.

If you wish to inspect and change the topic configurations, such as the retention settings, to match your disk space available for Kafka, please use the kafka-configs command. See below for an example, modifying the retention on the ingest queue to keep burst of data for up to one hour only.

global-events

This is LogScale's event-sourced database queue.

  • This queue has a relatively low throughput.

  • Allow messages of at least 2MB or more to allow large events:

    ini
    max.message.bytes=2097152

  • No log data is saved to this queue.

  • There should be a high number of replicas for this queue.

  • LogScale will raise the number of replicas on this queue to three if there are at least three brokers in the Kafka cluster and LogScale is allowed to manage the topic.

Default required replicas:

ini
min.insync.replicas = 2

Provided there are three brokers when LogScale creates the topic. Default retention configuration:

ini
retention.bytes = 1073741824

Which configures 1GB, and disable time based retention:

ini
retention.ms = -1

Compression should be set to:

ini
compression.type=producer
kafka-humio-ingest

Ingested events are sent to this queue, before they are stored in LogScale. LogScale's front end will accept ingest requests, parse them, and put them on the queue. LogScale's back end processes events from the queue and stores them into the datastore. This queue will have high throughput corresponding to the ingest load. The number of replicas can be configured in accordance with data size, latency and throughput requirements, and how important it is not to lose in-flight data.

LogScale defaults to two replicas on this queue, if at least two brokers exist in the Kafka cluster, and LogScale has not been told otherwise through the configuration parameter INGEST_QUEUE_REPLICATION_FACTOR, which defaults to 2. When data is stored in LogScale's own datastore, we don't need it on the queue any more.

  • Default required replicas:

    ini
    min.insync.replicas = $INGEST_QUEUE_REPLICATION_FACTOR - 1

    Provided there are enough brokers when LogScale creates the topic.

  • Default retention configuration (7 days as milliseconds):

    ini
    retention.ms = 604800000

  • Set the retention configuration on the humio-ingesttopic to:

    ini
    retention.bytes = disk_space_in_bytes_on_one_host / partitionCount

    with the actual setting based on the disk space available.

  • Compression should be set to:

    ini
    compression.type=producer

  • Allow messages of at least 8 MB to allow large events:

    ini
    max.message.bytes=8388608

  • Compaction is not allowed.

transientChatter-events

This queue is used for chatter between LogScale nodes. It is only used for transient data. LogScale will raise the number of replicas on this queue to 3 if there are at least three brokers in the Kafka cluster. The queue can have a short retention and it is not important to keep the data, as it gets stale very fast.

  • Default required replicas (provided there are three brokers when LogScale creates the topic):

    ini
    min.insync.replicas = 2

  • Default retention configuration (one hour as millis):

    ini
    retention.ms = 3600000

  • Compression should be set to:

    ini
    compression.type=producer

  • Support compaction settings allowing Kafka to retain only the latest copy:

    ini
    cleanup.policy=delete,compact

Kafka Version

LogScale recommends that the latest Kafka version is used with your LogScale deployment. The latest version of Kafka is available at Kafka Downloads.

Note

The minimum supported Kafka version is Kafka 2.4.1 and greater and is usually tested against the latest Kafka version.

You can set the configuration for individual topics using the following commands:

shell
## Example commands for setting protocol version on topic...
# See current config for topic, if any:
kafka-configs.sh --zookeeper localhost:2181 --describe --entity-type topics --entity-name 'humio-ingest'
# Set protocol version for topic:
kafka-configs.sh --zookeeper localhost:2181 --alter --entity-type topics --entity-name 'humio-ingest' --add-config 'message.format.version=0.11.0'
# Remove setting, allowing to use the default of the broker:
kafka-configs.sh --zookeeper localhost:2181 --alter --entity-type topics --entity-name 'humio-ingest' --delete-config 'message.format.version'