Stream Exporter Save

A Prometheus exporter for extracting metrics from streaming sources of text

Project README

Stream Exporter

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A Prometheus exporter for extracting metrics from streaming sources of text, such as logs written to a socket, or tailing a file. Extraction into metrics is done using regular expressions, on a per-line basis. Capture groups in the regular expression are used as labels in the metrics. All Prometheus metric types are supported, and fully configurable.

Inputs and patterns

The exporter works by reading from an input module, and then processing each line read with a number of configured metric patterns. Matching lines increment/set/observe their corresponding metric.

When testing configuration for the stream exporter, the file input module has a dryrun mode which runs an entire file through the configuration, and then prints the resulting metric output before exiting. See below for more information.

The exporter has multiple input modules, and one must be selected when starting the exporter using the -input.type flag. A list of all supported modules on your platform is returned when the -input.print flag is given. Details about the modules and their configuration are given below.

Metric patterns are configured with a yaml file, and consist of a listing all the patterns used for extraction. As an example, here is a simple configuration with two metrics:

  - name: comments_total
    kind: counter
    pattern: "^#.+"
  - name: current_visitors
    kind: gauge
    pattern: "Current number of visitors on (?P<section>\w+) is (?P<value>[0-9]+)"

The first one will create a counter comments_total, which will be incremented for every row starting with a #. This metric will not have any labels.

The second pattern is a gauge, with two capture groups, section and value. value is treated specially, and will be the value set on the gauge, while section will become a label on the metric. The output will be a metric like current_visitors{section="landing-page"} 432.


stream_exporter accepts a number of flags, most of which are related to the input modules. Those flags are described separately in the Inputs section below. The flags not configuring a specific input module are these:

Name Description Default value
-config Path to the pattern configuration file stream_exporter.yaml
-input.type What input module to use (Required)
-input.print Prints available input modules and exits -
-web.listen-address Address on which to expose metrics :9178
-web.metrics-path Path under which the metrics are available /metrics

Pattern configuration

The pattern configuration is a yaml file consisting of a top level list, metrics. The elements in this list have the following structure:

  - name: metric_name
    kind: metric_kind
    pattern: regular_expression
    <metric kind specific options>

The name field will become the name of the metric.

The kind field is the type of the metric, valid values are counter, gauge, summary and histogram.

The pattern field is a Golang regexp matching the lines you want to find. Named capture groups ((?P<name>CAPTURING_REGEXP)) are turned into labels. Exception to this is having a label value for gauges, summaries and histogram, where the matched number is what is set or observed (depending on the metric kind) for the metric.

Specific options

In addition to the above, histograms and summaries have a number of options that can be set.


For histograms, there is a single option, buckets, that can be configured.

  • buckets: A list of floating point numbers defining the upper bounds of each bucket


  - name: my_histogram
    kind: histogram
    pattern: I saw (?P<value>\d+) foos!
      - 1
      - 5
      - 10
      - 20


Summaries have a number of options, objectives, max_age, age_buckets and buf_cap.

  • objectives: A dictionary with floating point numbers as both keys and values. Defines the quantile rank estimates and their respective absolute error.
  • max_age: Defines the duration for which an observation stays relevant for the summary. Given as a string representation of a duration, for example 120s, 20m or 3d.
  • age_buckets: An integer. defining the number of buckets used to exclude observations that are older than MaxAge from the summary. A higher number has a resource penalty, so only increase it if the higher resolution is really required.
  • buf_cap: The sample stream buffer size. If there is a need to increase the value, a multiple of 500 is recommended.


  - name: my_summary
    kind: summary
    pattern: Found a foo in (?P<value>[\d\.]+) seconds!
      0.5: 0.5
      0.9: 0.1
      0.99: 0.01
    max_age: 15m
    age_buckets: 3
    buf_cap: 500

Input modules

A number of input modules are available, described here with their parameters.

Standard input

Reads from standard input.

The stdin input has two commandline flags:

  • input.stdin.quit-on-eof (Optional, default false): If true, the exporter will quit after getting to end of file. By default, it will keep running, and the metrics endpoint will still be available.
  • input.stdin.write-on-eof (Optional, default false): If true, all the collected metrics will be writted to stdout after getting to end of file. Useful in combination with quit-on-eof for configuration testing.


Reads lines from a file.

The file input has two parameters:

  • -input.file.path (Required) : The path to the file to read from.
  • -input.file.mode (Deprecated, Optional, default tail): tail or dryrun. In tail mode, the file is opened and any new lines written to the file is processed. In dryrun mode, the entire file is read and processed. When the end of the file is encountered, the current metrics state is written to standard out, and the exporter exits. Useful for debugging and configuration testing. NOTE: The dryrun mode is deprecated, and using the stdin input along with input.stdin.write-on-eof is recommended as a replacement.


Opens a socket for reading lines.

The socket input has two parameters:

  • (Optional, default tcp): The address family to open the socket. Valid values depend on platform, but include tcp and udp. On Linux and certain other systems, unix is also available.
  • input.socket.listenaddr (Required): The listen specification, for example :10000 to listen on all interfaces on port 10000.


Creates a syslog server which can act as a remote server from the local syslog server.

The syslog input has three parameters:

  • input.syslog.listenfamily (Required): The address family of the server. Valid values depend on platform, but include tcp and udp. On Linux and certain other systems, unix is also available.

  • input.syslog.listenaddr (Required): The listen specification, for example :1514 to listen on all interfaces on port 1514.

  • input.syslog.format (Optional, default autodetect): The format of the syslog messages. Defaults to automatic detection, can also be set to rfc3164, rfc5424 or rfc6587.

  • input.syslog.linetemplate (Optional, default [message][content]): The template to use to for lines passed to the pattern matcher. []-delimited words are substituted with the corresponding fields from the syslog message. Non-existing fields will be ignored. The following fields are available:

    All formats:

    • client
    • facility
    • hostname
    • priority
    • severity
    • timestamp
    • tls_peer

    RFC3164 only:

    • content
    • tag

    RFC5424 only:

    • app_name
    • message
    • msg_id
    • proc_id
    • version

    Since non-existing fields are ignored, the pattern [message][content] will contain the main part of the line regardless of which format is used.

Named pipe

Creates a named pipe to which lines can be written. Only available on Linux.

The namedpipe input has one parameter:

  • input.namedpipe.path (Required): The path where the pipe should be created. This may require elevated privileges to execute a mkfifo syscall.


The project uses govendor for dependency management. To build the exporter, call govendor build +p.

Open Source Agenda is not affiliated with "Stream Exporter" Project. README Source: carlpett/stream_exporter
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