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Fluentd

Loki has a Fluentd output plugin called fluent-plugin-grafana-loki that enables shipping logs to a private Loki instance or Grafana Cloud.

Installation

$ gem install fluent-plugin-grafana-loki

Usage

Note: use either <label>...</label> or extra_labels to set at least one label!

In your Fluentd configuration, use @type loki. Additional configuration is optional, default values would look like this:

<match **>
  @type loki
  url "https://logs-us-west1.grafana.net"
  username "#{ENV['LOKI_USERNAME']}"
  password "#{ENV['LOKI_PASSWORD']}"
  extra_labels {"env":"dev"}
  flush_interval 10s
  flush_at_shutdown true
  buffer_chunk_limit 1m
</match>

Using labels

Simple label from top level attribute

<match mytag>
  @type loki
  # ...
  <label>
    fluentd_worker
  </label>
  # ...
</match>

You can rewrite the label keys as well as the following

<match mytag>
  @type loki
  # ...
  <label>
    worker fluentd_worker
  </label>
  # ...
</match>

You can use record accessor syntax for nested field. https://docs.fluentd.org/plugin-helper-overview/api-plugin-helper-record_accessor#syntax

<match mytag>
  @type loki
  # ...
  <label>
    container $.kubernetes.container
  </label>
  # ...
</match>

Extracting Kubernetes labels

As Kubernetes labels are a list of nested key-value pairs there is a separate option to extract them. Note that special characters like ". - /" will be overwritten with _. Use with the remove_keys kubernetes option to eliminate metadata from the log.

<match mytag>
  @type loki
  # ...
  extract_kubernetes_labels true
  remove_keys kubernetes
  <label>
    container $.kubernetes.container
  </label>
  # ...
</match>

Multi-worker usage

Loki doesn't currently support out-of-order inserts - if you try to insert a log entry an earlier timestamp after a log entry with identical labels but a later timestamp, the insert will fail with HTTP status code: 500, message: rpc error: code = Unknown desc = Entry out of order. Therefore, in order to use this plugin in a multi worker Fluentd setup, you'll need to include the worker ID in the labels or otherwise ensure log streams are always sent to the same worker.

For example, using fluent-plugin-record-modifier:

<filter mytag>
    @type record_modifier
    <record>
        fluentd_worker "#{worker_id}"
    </record>
</filter>

<match mytag>
  @type loki
  # ...
  <label>
    fluentd_worker
  </label>
  # ...
</match>

Using multiple buffer flush threads

Similarly, when using flush_thread_count > 1 in the buffer section, a thread identifier must be added as a label to ensure that log chunks flushed in parallel to loki by fluentd always have increasing times for their unique label sets.

This plugin automatically adds a fluentd_thread label with the name of the buffer flush thread when flush_thread_count > 1.

Docker Image

There is a Docker image grafana/fluent-plugin-grafana-loki:master which contains default configuration files. By default, fluentd containers use the configurations but you can also specify your fluentd.conf with FLUENTD_CONF environment variable.

This image also uses LOKI_URL, LOKI_USERNAME, and LOKI_PASSWORD environment variables to specify the Loki's endpoint, user, and password (you can leave the USERNAME and PASSWORD blank if they're not used).

Example

A Docker Compose configuration that will work looks like:

services:
  fluentd:
    image: grafana/fluent-plugin-grafana-loki:master
    command:
      - "fluentd"
      - "-v"
      - "-p"
      - "/fluentd/plugins"
    environment:
      LOKI_URL: http://loki:3100
      LOKI_USERNAME:
      LOKI_PASSWORD:
    deploy:
      mode: global
    configs:
      - source: loki_config
        target: /fluentd/etc/loki/loki.conf
    networks:
      - loki
    volumes:
      - host_logs:/var/log
      # Needed for journald log ingestion:
      - /etc/machine-id:/etc/machine-id
      - /dev/log:/dev/log
      - /var/run/systemd/journal/:/var/run/systemd/journal/
    logging:
      options:
         tag: infra.monitoring

Configuration

url

The url of the Loki server to send logs to. When sending data the publish path (/api/prom/push) will automatically be appended. By default the url is set to https://logs-us-west1.grafana.net, the url of the Grafana Labs preview (hosted Loki)[https://grafana.com/loki] service.

Proxy Support

Starting with version 0.8.0, this gem uses excon, which supports proxy with environment variables - https://github.com/excon/excon#proxy-support

username / password

Specify a username and password if the Loki server requires authentication. If using the GrafanaLab's hosted Loki, the username needs to be set to your instanceId and the password should be a Grafana.com api key.

tenant

Loki is a multi-tenant log storage platform and all requests sent must include a tenant. For some installations the tenant will be set automatically by an authenticating proxy. Otherwise you can define a tenant to be passed through. The tenant can be any string value.

client certificate verification

Specify a pair of client certificate and private key with cert and key if a reverse proxy with client certificate verification is configured in front of Loki. ca_cert can also be specified if the server uses custom certificate authority.

<match **>
  @type loki

  url "https://loki"

  cert /path/to/certificate.pem
  key /path/to/key.key
  ca_cert /path/to/ca.pem

  ...
</match>

output format

Loki is intended to index and group log streams using only a small set of labels. It is not intended for full-text indexing. When sending logs to Loki the majority of log message will be sent as a single log "line".

There are few configurations settings to control the output format.

  • extra_labels: (default: nil) set of labels to include with every Loki stream. eg {"env":"dev", "datacenter": "dc1"}
  • remove_keys: (default: nil) comma separated list of needless record keys to remove. All other keys will be placed into the log line. You can use record_accessor syntax.
  • line_format: format to use when flattening the record to a log line. Valid values are "json" or "key_value". If set to "json" the log line sent to Loki will be the fluentd record (excluding any keys extracted out as labels) dumped as json. If set to "key_value", the log line will be each item in the record concatenated together (separated by a single space) in the format <key>=<value>.
  • drop_single_key: if set to true and a record only has 1 key after extracting <label></label> blocks, set the log line to the value and discard the key.

Buffer options

fluentd-plugin-loki extends Fluentd's builtin Output plugin and use compat_parameters plugin helper. It adds the following options:

buffer_type memory
flush_interval 10s
retry_limit 17
retry_wait 1.0
num_threads 1