12.4. Kafka Command-Line Tools¶
The GeoMesa Kafka distribution includes a set of command-line tools for feature management, ingest, export and debugging.
To install the tools, see Setting up the Kafka Command Line Tools.
Once installed, the tools should be available through the command geomesa-kafka:
$ geomesa-kafka
INFO Usage: geomesa-kafka [command] [command options]
Commands:
...
Commands that are common to multiple back ends are described in Command-Line Tools. The commands here are Kafka-specific.
12.4.1. General Arguments¶
Most commands require you to specify the connection to Kafka. This generally includes the list of
Kafka brokers and Zookeeper servers. Specify brokers with the --brokers (or -b) argument, and
specify Zookeepers with --zookeepers (or -z).
Kafka stores metadata under a particular path in Zookeeper - this can be thought of as a namespace
for feature types. Use --zkpath (or -p) to override the default path.
12.4.2. Commands¶
12.4.2.1. create-schema¶
See create-schema for an overview of this command.
In addition to the regular options, Kafka allows the number of partitions and the replication factor of the Kafka topic to be specified.
| Argument | Description |
|---|---|
--partitions |
The number of partitions used for the Kafka topic |
--replication |
The replication factor for the Kafka topic |
12.4.2.2. export¶
See export for an overview of this command.
Unlike the standard export, this command will not not terminate until it is cancelled (through a shell interrupt)
or until --max-features have been read. Thus, it can be used to monitor a topic.
This command differs from the listen command (below) in that it allows filtering and output in various formats.
It will also ignore drop and clear messages generated by feature deletion.
In addition to the regular options, Kafka allows control over the consumer behavior:
| Argument | Description |
|---|---|
--from-beginning |
Start reading messages from the beginning of the Kafka topic, instead of the end |
--num-consumers |
Number of consumers used to read the topic |
The --num-consumers argument can be used to increase read speed. However, there can be at most one
consumer per topic partition.
The --from-beginning argument can be used to start reading the Kafka topic from the start. Otherwise,
only new messages that are sent after this command is invoked will be read.
12.4.2.3. ingest¶
See ingest for an overview of this command.
In addition to the regular options, Kafka allows the number of partitions and the replication factor of the Kafka topic to be specified. In addition, an artificial delay can be inserted to simulate a live data stream.
| Argument | Description |
|---|---|
--partitions |
The number of partitions used for the Kafka topic |
--replication |
The replication factor for the Kafka topic |
--delay |
The delay inserted between messages |
The --delay argument should be specified as a duration, in plain language. For example, 100 millis
or 1 second. The ingest will pause after creating each SimpleFeature for the specified delay.
This can be used to simulate a live data stream.
12.4.2.4. listen¶
This command behaves similarly to the export command (above), but it does not provide options
for filtering or output format. It will show each message on the Kafka topic, including drop and
clear messages generated from feature deletion.
This command will not not terminate until it is cancelled (through a shell interrupt).
| Argument | Description |
|---|---|
-f, --feature-name * |
The name of the schema |
--from-beginning |
Start reading messages from the beginning of the Kafka topic, instead of the end |
--num-consumers |
Number of consumers used to read the topic |
The --num-consumers argument can be used to increase read speed. However, there can be at most one
consumer per topic partition.
The --from-beginning argument can be used to start reading the Kafka topic from the start. Otherwise,
only new messages that are sent after this command is invoked will be read.