exec_filter

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exec_filter
The out_exec_filter Buffered Output plugin (1) executes an external program using an event as input and (2) reads a new event from the program output. It passes tab-separated values (TSV) to stdin and reads TSV from stdout by default.
Example Configuration
out_exec_filter is included in Fluentd's core. No additional installation process is required.
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<match pattern>
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  @type exec_filter
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  command cmd arg arg
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  in_keys k1,k2,k3
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  out_keys k1,k2,k3,k4
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  tag_key k1
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  time_key k2
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  time_format %Y-%m-%d %H:%M:%S
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</match>
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Please see the Config File article for the basic structure and syntax of the configuration file.
Parameters
type (required)
The value must be exec_filter.
command (required)
The command (program) to execute. The out_exec_filter plugin passes the incoming event to the program input and receives the filtered event from the program output.
num_children
The number of spawned process for command. Default is 1.
If the number is larger than 2, fluentd uses spawned processes by round robin fashion.
child_respawn
Respawn command when command exit. Default is disabled.
If you specify a positive number, try to respawn until specified times. If you specify inf or -1, try to respawn forever.
in_format
The format used to map the incoming event to the program input.
The following formats are supported:
tsv (default)
When using the tsv format, please also specify the comma-separated in_keys parameter.
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in_keys k1,k2,k3
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json
msgpack
out_format
The format used to process the program output.
The following formats are supported:
tsv (default)
When using the tsv format, please also specify the comma-separated out_keys parameter.
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out_keys k1,k2,k3,k4
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json
msgpack
When using the json format, this plugin uses the Yajl library to parse the program output. Yajl buffers data internally so the output isn't always instantaneous.
tag_key
The name of the key to use as the event tag. This replaces the value in the event record.
time_key
The name of the key to use as the event time. This replaces the the value in the event record.
time_format
The format for event time used when the time_key parameter is specified. The default is UNIX time (integer).
Buffered Output Parameters
For advanced usage, you can tune Fluentd's internal buffering mechanism with these parameters.
buffer_type
The buffer type is memory by default (buf_memory) for the ease of testing, however file (buf_file) buffer type is always recommended for the production deployments. If you use file buffer type, buffer_path parameter is required.
buffer_queue_limit, buffer_chunk_limit
The length of the chunk queue and the size of each chunk, respectively. Please see the Buffer Plugin Overview article for the basic buffer structure. The default values are 64 and 8m, respectively. The suffixes "k" (KB), "m" (MB), and "g" (GB) can be used for buffer_chunk_limit.
flush_interval
The interval between data flushes. The default is 60s. The suffixes "s" (seconds), "m" (minutes), and "h" (hours) can be used.
flush_at_shutdown
If set to true, Fluentd waits for the buffer to flush at shutdown. By default, it is set to true for Memory Buffer and false for File Buffer.
retry_wait, max_retry_wait
The initial and maximum intervals between write retries. The default values are 1.0 seconds and unset (no limit). The interval doubles (with +/-12.5% randomness) every retry until max_retry_wait is reached.
Since td-agent will retry 17 times before giving up by default (see the retry_limit parameter for details), the sleep interval can be up to approximately 131072 seconds (roughly 36 hours) in the default configurations.
retry_limit, disable_retry_limit
The limit on the number of retries before buffered data is discarded, and an option to disable that limit (if true, the value of retry_limit is ignored and there is no limit). The default values are 17 and false (not disabled). If the limit is reached, buffered data is discarded and the retry interval is reset to its initial value (retry_wait).
num_threads
The number of threads to flush the buffer. This option can be used to parallelize writes into the output(s) designated by the output plugin. Increasing the number of threads improves the flush throughput to hide write / network latency. The default is 1.
slow_flush_log_threshold
The threshold for checking chunk flush performance. The default value is 20.0 seconds. Note that parameter type is float, not time.
If chunk flush takes longer time than this threshold, fluentd logs warning message like below:
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2016-12-19 12:00:00 +0000 [warn]: buffer flush took longer time than slow_flush_log_threshold: elapsed_time = 15.0031226690043695 slow_flush_log_threshold=10.0 plugin_id="foo"
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log_level option
The log_level option allows the user to set different levels of logging for each plugin. The supported log levels are: fatal, error, warn, info, debug, and trace.
Please see the logging article for further details.
Script example
Here is an example writtein in ruby.
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require 'json'
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require 'msgpack'
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​
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begin
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  while line = STDIN.gets # continue to read a event from stdin
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    line.chomp!
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​
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    # Input format depends on exec_filter's in_format setting
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    json = JSON.parse(line)
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​
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    # main processing. You can do anything, mutate record, access to database and etc.
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    json['new_field'] = "Hey from exec_filter script!"
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​
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    # Write data to stdout. Output format depends on exec_filter's out_format setting
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    STDOUT.print MessagePack.pack(json)
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​
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    # Call flush to avoid buffering events
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    STDOUT.flush
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  end
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rescue Interrupt # Ignore Interrupt exception because it happens during exec_filter shutdown
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end
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Corresponding configuration is below:
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<match test.**>
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  @type exec_filter
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  command ruby /path/to/ruby_script.rb
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  in_format json
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  out_format msgpack
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  flush_interval 10s
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  tag filtered.exec
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</match>
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If you want to use other language, translate above script example into your language.
If this article is incorrect or outdated, or omits critical information, please let us know. Fluentd is a open source project under Cloud Native Computing Foundation (CNCF). All components are available under the Apache 2 License.
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Last modified 1yr ago