fluent-plugin-prometheus, a plugin for Fluentd

A fluent plugin that instruments metrics from records and exposes them via web interface. Intended to be used together with a Prometheus server.

Since v1.8.0, fluent-plugin-prometheus uses http_server helper to launch HTTP server. If you want to handle lots of connections, install async-http gem.

Add this line to your application's Gemfile:

gem 'fluent-plugin-prometheus'

And then execute:

$ bundle

Or install it yourself as:

$ gem install fluent-plugin-prometheus

fluentd-plugin-prometheus includes 6 plugins.

• prometheus input plugin
• prometheus_monitor input plugin
• prometheus_output_monitor input plugin
• prometheus_tail_monitor input plugin
• prometheus output plugin
• prometheus filter plugin

See sample configuration, or try tutorial.

You have to configure this plugin to expose metrics collected by other Prometheus plugins. This plugin provides a metrics HTTP endpoint to be scraped by a Prometheus server on 24231/tcp(default).

With following configuration, you can access http://localhost:24231/metrics on a server where fluentd running.

<source>
  @type prometheus
</source>

More configuration parameters:

• bind: binding interface (default: '0.0.0.0')
• port: listen port (default: 24231)
• metrics_path: metrics HTTP endpoint (default: /metrics)
• aggregated_metrics_path: metrics HTTP endpoint (default: /aggregated_metrics)
• content_encoding: encoding format for the exposed metrics (default: identity). Supported formats are {identity, gzip}

When using multiple workers, each worker binds to port + fluent_worker_id. To scrape metrics from all workers at once, you can access http://localhost:24231/aggregated_metrics.

Use <trasnport tls>. See transport config article for more details.

<source>
  @type prometheus
  <transport tls>
    # TLS parameters...
  </transport
</source>

This plugin collects internal metrics in Fluentd. The metrics are similar to/part of monitor_agent.

• fluentd_status_buffer_queue_length
• fluentd_status_buffer_total_bytes
• fluentd_status_retry_count
• fluentd_status_buffer_newest_timekey from fluentd v1.4.2
• fluentd_status_buffer_oldest_timekey from fluentd v1.4.2

With following configuration, those metrics are collected.

<source>
  @type prometheus_monitor
</source>

More configuration parameters:

• <labels>: additional labels for this metric (optional). See Labels
• interval: interval to update monitor_agent information in seconds (default: 5)

This plugin collects internal metrics for output plugin in Fluentd. This is similar to prometheus_monitor plugin, but specialized for output plugin. There are Many metrics prometheus_monitor does not include, such as num_errors, retry_wait and so on.

Metrics for output

• fluentd_output_status_retry_count
• fluentd_output_status_num_errors
• fluentd_output_status_emit_count
• fluentd_output_status_retry_wait
  • current retry_wait computed from last retry time and next retry time
• fluentd_output_status_emit_records
• fluentd_output_status_write_count
• fluentd_output_status_rollback_count
• fluentd_output_status_flush_time_count in milliseconds from fluentd v1.6.0
• fluentd_output_status_slow_flush_count from fluentd v1.6.0

Metrics for buffer

• fluentd_output_status_buffer_total_bytes
• fluentd_output_status_buffer_stage_length from fluentd v1.6.0
• fluentd_output_status_buffer_stage_byte_size from fluentd v1.6.0
• fluentd_output_status_buffer_queue_length
• fluentd_output_status_buffer_queue_byte_size from fluentd v1.6.0
• fluentd_output_status_buffer_newest_timekey from fluentd v1.6.0
• fluentd_output_status_buffer_oldest_timekey from fluentd v1.6.0
• fluentd_output_status_buffer_available_space_ratio from fluentd v1.6.0

With following configuration, those metrics are collected.

<source>
  @type prometheus_output_monitor
</source>

More configuration parameters:

• <labels>: additional labels for this metric (optional). See Labels
• interval: interval to update monitor_agent information in seconds (default: 5)
• gauge_all: Specify metric type. If true, use gauge type. If false, use counter type. Since v2, this parameter will be removed and use counter type.

This plugin collects internal metrics for in_tail plugin in Fluentd. in_tail plugin holds internal state for files that the plugin is watching. The state is sometimes important to monitor plugins work correctly.

This plugin uses internal class of Fluentd, so it's easy to break.

• fluentd_tail_file_position: Current bytes which plugin reads from the file
• fluentd_tail_file_inode: inode of the file
• fluentd_tail_file_closed: Number of closed files
• fluentd_tail_file_opened: Number of opened files
• fluentd_tail_file_rotated: Number of rotated files
• fluentd_tail_file_throttled: Number of times files got throttled (only with fluentd version > 1.17)

Default labels:

• plugin_id: a value set for a plugin in configuration.
• type: plugin name. in_tail only for now.
• path: file path

With following configuration, those metrics are collected.

<source>
  @type prometheus_tail_monitor
</source>

More configuration parameters:

• <labels>: additional labels for this metric (optional). See Labels
• interval: interval to update monitor_agent information in seconds (default: 5)

Both output/filter plugins instrument metrics from records. Both plugins have no impact against values of each records, just read.

Assuming you have following configuration and receiving message,

<match message>
  @type stdout
</match>

message {
  "foo": 100,
  "bar": 200,
  "baz": 300
}

In filter plugin style,

<filter message>
  @type prometheus
  <metric>
    name message_foo_counter
    type counter
    desc The total number of foo in message.
    key foo
  </metric>
</filter>

<match message>
  @type stdout
</match>

In output plugin style:

<filter message>
  @type prometheus
  <metric>
    name message_foo_counter
    type counter
    desc The total number of foo in message.
    key foo
  </metric>
</filter>

<match message>
  @type copy
  <store>
    @type prometheus
    <metric>
      name message_foo_counter
      type counter
      desc The total number of foo in message.
      key foo
    </metric>
  </store>
  <store>
    @type stdout
  </store>
</match>

With above configuration, the plugin collects a metric named message_foo_counter from key foo of each records.

You can access nested keys in records via dot or bracket notation (https://docs.fluentd.org/plugin-helper-overview/api-plugin-helper-record_accessor#syntax), for example: $.kubernetes.namespace, $['key1'][0]['key2']. The record accessor is enable only if the value starts with $. or $[.

See Supported Metric Type and Labels for more configuration parameters.

For details of each metric type, see Prometheus documentation. Also see metric name guide.

<metric>
  name message_foo_counter
  type counter
  desc The total number of foo in message.
  key foo
  <labels>
    tag ${tag}
    host ${hostname}
    foo bar
  </labels>
</metric>

• name: metric name (required)
• type: metric type (required)
• desc: description of this metric (required)
• key: key name of record for instrumentation (optional)
• initialized: boolean controlling initilization of metric (optional). See Metric initialization
• <labels>: additional labels for this metric (optional). See Labels
• <initlabels>: labels to use for initialization of ReccordAccessors/Placeholder labels (optional). See Metric initialization

If key is empty, the metric values is treated as 1, so the counter increments by 1 on each record regardless of contents of the record.

<metric>
  name message_foo_gauge
  type gauge
  desc The total number of foo in message.
  key foo
  <labels>
    tag ${tag}
    host ${hostname}
    foo bar
  </labels>
</metric>

• name: metric name (required)
• type: metric type (required)
• desc: description of metric (required)
• key: key name of record for instrumentation (required)
• initialized: boolean controlling initilization of metric (optional). See Metric initialization
• <labels>: additional labels for this metric (optional). See Labels
• <initlabels>: labels to use for initialization of ReccordAccessors/Placeholder labels (optional). See Metric initialization

<metric>
  name message_foo
  type summary
  desc The summary of foo in message.
  key foo
  <labels>
    tag ${tag}
    host ${hostname}
    foo bar
  </labels>
</metric>

• name: metric name (required)
• type: metric type (required)
• desc: description of metric (required)
• key: key name of record for instrumentation (required)
• initialized: boolean controlling initilization of metric (optional). See Metric initialization
• <labels>: additional labels for this metric (optional). See Labels
• <initlabels>: labels to use for initialization of ReccordAccessors/Placeholder labels (optional). See Metric initialization

<metric>
  name message_foo
  type histogram
  desc The histogram of foo in message.
  key foo
  buckets 0.1, 1, 5, 10
  <labels>
    tag ${tag}
    host ${hostname}
    foo bar
  </labels>
</metric>

• name: metric name (required)
• type: metric type (required)
• desc: description of metric (required)
• key: key name of record for instrumentation (required)
• initialized: boolean controlling initilization of metric (optional). See Metric initialization
• buckets: buckets of record for instrumentation (optional)
• <labels>: additional labels for this metric (optional). See Labels
• <initlabels>: labels to use for initialization of ReccordAccessors/Placeholder labels (optional). See Metric initialization

See Prometheus Data Model first.

You can add labels with static value or dynamic value from records. In prometheus_monitor input plugin, you can't use label value from records.

<labels>
  key1 value1
  key2 value2
</labels>

All labels sections has same format. Each lines have key/value for label.

You can access nested fields in records via dot or bracket notation (https://docs.fluentd.org/plugin-helper-overview/api-plugin-helper-record_accessor#syntax), for example: $.kubernetes.namespace, $['key1'][0]['key2']. The record accessor is enable only if the value starts with $. or $[. Other values are handled as raw string as is and may be expanded by placeholder described later.

You can use placeholder for label values. The placeholders will be expanded from reserved values and records. If you specify ${hostname}, it will be expanded by value of a hostname where fluentd runs. The placeholder for records is deprecated. Use record accessor syntax instead.

Reserved placeholders are:

• ${hostname}: hostname
• ${worker_id}: fluent worker id
• ${tag}: tag name
  • only available in Prometheus output/filter plugin
• ${tag_parts[N]} refers to the Nth part of the tag.
  • only available in Prometheus output/filter plugin
• ${tag_prefix[N]} refers to the [0..N] part of the tag.
  • only available in Prometheus output/filter plugin
• ${tag_suffix[N]} refers to the [tagsize-1-N..] part of the tag.
  • where tagsize is the size of tag which is splitted with . (when tag is 1.2.3, then tagsize is 3)
  • only available in Prometheus output/filter plugin

You can configure if a metric should be initialized to its zero value before receiving any event. To do so you just need to specify initialized true.

<metric>
  name message_bar_counter
  type counter
  desc The total number of bar in message.
  key bar
  initialized true
  <labels>
    foo bar
  </labels>
</metric>

If your labels contains ReccordAccessors or Placeholders, you must use <initlabels> to specify the values your ReccordAccessors/Placeholders will take. This feature is useful only if your Placeholders/ReccordAccessors contain deterministic values. Initialization will create as many zero value metrics as <initlabels> blocks you defined. Potential reserved placeholders ${hostname} and ${worker_id}, as well as static labels, are automatically added and should not be specified in <initlabels> configuration.

<metric>
  name message_bar_counter
  type counter
  desc The total number of bar in message.
  key bar
  initialized true
  <labels>
    key $.foo
    tag ${tag}
    foo bar
    worker_id ${worker_id}
  </labels>
  <initlabels>
    key foo1
    tag tag1
  </initlabels>
  <initlabels>
    key foo2
    tag tag2
  </initlabels>
</metric>
<labels>
  hostname ${hostname}
</labels>

Prometheus output/filter plugin can have multiple metric section. Top-level labels section specifies labels for all metrics. Labels section inside metric section specifies labels for the metric. Both are specified, labels are merged.

<filter message>
  @type prometheus
  <metric>
    name message_foo_counter
    type counter
    desc The total number of foo in message.
    key foo
    <labels>
      key foo
      data_type ${type}
    </labels>
  </metric>
  <metric>
    name message_bar_counter
    type counter
    desc The total number of bar in message.
    key bar
    <labels>
      key bar
    </labels>
  </metric>
  <labels>
    tag ${tag}
    hostname ${hostname}
  </labels>
</filter>

In this case, message_foo_counter has tag, hostname, key and data_type labels.

Checkout repository and setup.

$ git clone git://github.com/fluent/fluent-plugin-prometheus.git
$ cd fluent-plugin-prometheus
$ bundle install --path vendor/bundle

Download pre-compiled Prometheus binary and start it. It listens on 9090.

$ wget https://github.com/prometheus/prometheus/releases/download/v1.5.2/prometheus-1.5.2.linux-amd64.tar.gz -O - | tar zxf -
$ ./prometheus-1.5.2.linux-amd64/prometheus -config.file=./misc/prometheus.yaml -storage.local.path=./prometheus/metrics

Install Nginx for sample metrics. It listens on 80 and 9999.

$ sudo apt-get install -y nginx
$ sudo cp misc/nginx_proxy.conf /etc/nginx/sites-enabled/proxy
$ sudo chmod 777 /var/log/nginx && sudo chmod +r /var/log/nginx/*.log
$ sudo service nginx restart

Start fluentd with sample configuration. It listens on 24231.

$ bundle exec fluentd -c misc/fluentd_sample.conf -v

Generate some records by accessing nginx.

$ curl http://localhost/
$ curl http://localhost:9999/

Confirm that some metrics are exported via Fluentd.

$ curl http://localhost:24231/metrics

Then, make a graph on Prometheus UI. http://localhost:9090/

1. Fork it ( https://github.com/fluent/fluent-plugin-prometheus/fork )
2. Create your feature branch (git checkout -b my-new-feature)
3. Commit your changes (git commit -am 'Add some feature')
4. Push to the branch (git push origin my-new-feature)
5. Create a new Pull Request