Loki

Loki is multi-tenant log aggregation system inspired by Prometheus.

The Fluent Bit Loki built-in output plugin lets you send your log or events to a Loki service. It supports data enrichment with Kubernetes labels, custom label keys, and Tenant ID, along with other information.

There is a separate Golang output plugin provided by Grafana with different configuration options.

Configuration parameters

Key

Description

Default

host

Loki base hostname or IP address. Don't include the sub-path, only the base hostname or URL.

127.0.0.1

uri

Specify a custom HTTP URI. It must start with a forward slash (/).

/loki/api/v1/push

port

The Loki TCP port.

3100

tls

Use TLS authentication.

off

http_user

Set HTTP basic authentication user name.

none

http_passwd

Set HTTP basic authentication password.

none

bearer_token

Set bearer token authentication token value.

none

header

Add additional arbitrary HTTP header key/value pair. Multiple headers can be set.

none

tenant_id

Tenant ID used by default to push logs to Loki. If omitted or empty it assumes Loki is running in single-tenant mode and no X-Scope-OrgID header is sent.

none

labels

Stream labels for API request. It can be multiple comma separated of strings specifying key=value pairs. Allows fixed parameters, or adding custom record keys (similar to the label_keys property). See the Labels section.

job=fluent-bit

label_keys

(Optional.) List of record keys that will be placed as stream labels. This configuration property is for records key only. See the Labels section.

none

label_map_path

Specify the label map path. The file defines how to extract labels from each record. See the Labels section.

none

structured_metadata

(Optional.) Comma-separated list of key=value strings specifying structured metadata for the log line. Like the labels parameter, values can reference record keys using record accessors. See Use structured_metadata..

none

structured_metadata_map_keys

(Optional.) Comma-separated list of record key strings specifying record values of type map, used to dynamically populate structured metadata for the log line. Values can only reference record keys using record accessors, which should reference map values. Each entry from the referenced map will be used to add an entry to the structured metadata. See Use structured_metadata..

none

remove_keys

(Optional.) List of keys to remove.

none

drop_single_key

When set to true and after extracting labels only a single key remains, the log line sent to Loki will be the value of that key in line_format. If set to raw and the log line is a string, the log line will be sent unquoted.

off

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 Fluent Bit record 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.

json

auto_kubernetes_labels

If set to true, adds all Kubernetes labels to the Stream labels.

off

tenant_id_key

Specify the name of the key from the original record that contains the Tenant ID. The value of the key is set as X-Scope-OrgID of HTTP header. Use to set Tenant ID dynamically.

none

compress

Set payload compression mechanism. The only available option is gzip.

"" (no compression)

workers

The number of workers to perform flush operations for this output.

0

Labels

Loki stores the record logs inside Streams. A stream is defined by a set of labels, and at least one label is required.

Fluent Bit implements a flexible mechanism to set labels by using fixed key/value pairs of text. It also allows setting as labels certain keys that exists as part of the records that are being processed.

Consider the following JSON record (pretty printed for readability):

{
  "key": 1,
  "sub": {
    "stream": "stdout",
    "id": "some id"
  },
  "kubernetes": {
    "labels": {
      "team": "Santiago Wanderers"
    }
  }
}

If you decide that your Loki Stream will be composed by two labels called job and the value of the record key called stream , your labels configuration properties might look something like the following:

pipeline:

  outputs:
    - name: loki
      match: '*'
      labels: job=fluentbit, $sub['stream']

The label job has the value fluentbit and the second label is configured to access the nested map called sub targeting the value of the key stream .

The second label name must start with a dollar sign $, meaning it's a Record Accessor pattern, which provides the ability to retrieve values from nested maps by using the key names.

When processing the previous configuration, internally the ending labels for the stream in question becomes:

job="fluentbit", stream="stdout"

Another feature of Labels management is the ability to provide custom key names. Using the same record accessor pattern you can specify the key name manually and let the value populate automatically at runtime:

pipeline:

  outputs:
    - name: loki
      match: '*'
      labels: job=fluentbit, mystream=$sub['stream']

When processing that new configuration, the internal labels will be:

job="fluentbit", mystream="stdout"

Use `label_keys`

The label_keys configuration property lets you specify multiple record keys which need to be placed as part of the outgoing Stream Labels. This is another way to set a record key in the Stream, but with the limitation that you can't use a custom name for the key value.

The following configuration examples generate the same Stream Labels:

pipeline:

  outputs:
    - name: loki
      match: '*'
      labels: job=fluentbit
      label_keys: $sub['stream']

The previous configuration accomplishes the same as this one:

pipeline:

  outputs:
    - name: loki
      match: '*'
      labels: job=fluentbit, $sub['stream']

Both generate the following Streams label:

job="fluentbit", stream="stdout"

Use `label_map_path`

The label_map_path configuration property reads a JSON file that defines how to extract labels from each record.

The file should contain a JSON object. Each key defines how to get label value from a nested record. Each value is used as a label name.

The following configuration examples generate the same Stream Labels:

map.json:

{
  "sub": {
    "stream": "stream"
  }
}

Add the JSON path to the plugin output configuration:

pipeline:

  outputs:
    - name: loki
      match: '*'
      label_map_path: /path/to/map.json

The previous configurations accomplish the same as this one:

pipeline:

  outputs:
    - name: loki
      match: '*'
      labels: job=fluentbit, $sub['stream']

Both will generate the following Streams label:

job="fluentbit", stream="stdout"

Kubernetes and labels

If you're running in a Kubernetes environment, consider enabling the auto_kubernetes_labels option, which populates the streams with the Pod labels for you. Consider the following configuration:

pipeline:

  outputs:
    - name: loki
      match: '*'
      labels: job=fluentbit
      auto_kubernetes_labels: on

Based on the JSON example provided, the internal stream labels will be:

job="fluentbit", team="Santiago Wanderers"

Use `drop_single_key`

If there's only one key remaining after removing keys, you can use the drop_single_key property to send its value to Loki, rather than a single key=value pair.

Consider this JSON example:

{"key":"value"}

If the value is a string, line_format is json, and drop_single_key is true, it will be sent as a quoted string.

pipeline:

  outputs:
    - name: loki
      match: '*'
      drop_single_key: on
      line_format: json

The outputted line would show in Loki as:

"value"

If drop_single_key is raw, or line_format is key_value, it will show in Loki as:

value

If you want both structured JSON and plain text logs in Loki, set drop_single_key to raw and line_format to json. Loki doesn't interpret a quoted string as valid JSON. To remove the quotes without drop_single_key set to raw, use a query like this:

{"job"="fluent-bit"} | regexp `^"?(?P<log>.*?)"?$` | line_format "{{.log}}"

If drop_single_key is off, it will show in Loki as:

{"key":"value"}

You can get the same behavior this flag provides in Loki with drop_single_key set to off with this query:

{"job"="fluent-bit"} | json | line_format "{{.log}}"

Use `structured_metadata`

Structured metadata lets you attach custom fields to individual log lines without embedding the information in the content of the log line. This capability works well for high cardinality data that isn't suited for using labels. Although not a label, the structured_metadata configuration parameter operates similarly to the labels parameter. Both parameters are comma-delimited key=value lists, and both can use record accessors to reference keys within the record being processed.

The following configuration:

Defines fixed values for the cluster and region labels.
Uses the record accessor pattern to set the namespace label to the namespace name as determined by the Kubernetes metadata filter (not shown).
Uses a structured metadata field to hold the Kubernetes pod name.

pipeline:

  outputs:
    - name: loki
      match: '*'
      labels: cluster=my-k8s-cluster, region=us-east-1, namespace=$kubernetes['namespace_name']
      structured_metadata: pod=$kubernetes['pod_name']

[OUTPUT]
  name                loki
  match               *
  labels              cluster=my-k8s-cluster, region=us-east-1, namespace=$kubernetes['namespace_name']
  structured_metadata pod=$kubernetes['pod_name']

Other common uses for structured metadata include trace and span IDs, process and thread IDs, and log levels.

Structured metadata is officially supported starting with Loki 3.0, and shouldn't be used with Loki deployments prior to Loki 3.0.

Structured metadata maps

In addition to the structured_metadata configuration parameter, a structured_metadata_map_keys is available, which can be used to dynamically populate structured metadata from map values in the log record. structured_metadata_map_keys can be set with a list of record accessors, where each one should reference map values in the log record. Record accessors which don't match a map value will be skipped.

The following configuration is similar to the previous example, except now all entries in the log record map value $kubernetes will be used as structured metadata entries:

pipeline:

  outputs:
    - name: loki
      match: '*'
      labels: cluster=my-k8s-cluster, region=us-east-1
      structured_metadata_map_keys: $kubernetes

Assuming the value $kubernetes is a map containing two entries namespace_name and pod_name, the previous configuration is equivalent to:

pipeline:

  outputs:
    - name: loki
      match: '*'
      labels: cluster=my-k8s-cluster, region=us-east-1
      structured_metadata: $kubernetes['namespace_name'], $kubernetes['pod_name']

[OUTPUT]
  name                loki
  match               *
  labels              cluster=my-k8s-cluster, region=us-east-1
  structured_metadata $kubernetes['namespace_name'],$kubernetes['pod_name']

Networking and TLS configuration

This plugin inherits core Fluent Bit features to customize the network behavior and optionally enable TLS in the communication channel. For more details about the specific options available, refer to the following articles:

Networking Setup: timeouts, keepalive and source address
Security and TLS: all about TLS configuration and certificates

All options mentioned in these articles must be enabled in the plugin configuration in question.

Fluent Bit and Grafana Cloud

Fluent Bit supports sending logs and metrics to Grafana Cloud by providing the appropriate URL and ensuring TLS is enabled.

The following samples show example configurations. Be sure to set the credentials (shown here with XXX) and ensure the host URL matches the correct one for your deployment:

pipeline:

  outputs:
    - name: loki
      match: '*'
      host: logs-prod-eu-west-0.grafana.net
      port: 433
      tls: on
      tls.verify: on
      http_user: XXX
      http_password: XXX

Get started

The following configuration example emits a dummy example record and ingests it on Loki. Copy and paste the following content into a file out_loki.yaml or out_loki.conf:

service:
  flush: 1
  log_level: info

pipeline:
  inputs:
    - name: dummy
      dummy: '{"key": 1, "sub": {"stream": "stdout", "id": "some id"}, "kubernetes": {"labels": {"team": "Santiago Wanderers"}}}'
      samples: 1

  outputs:
    - name: loki
      match: '*'
      host: 127.0.0.1
      port: 3100
      labels: job=fluentbit
      label_keys: $sub['stream']
      auto_kubernetes_labels: on

[SERVICE]
  flush     1
  log_level info

[INPUT]
  name      dummy
  dummy     {"key": 1, "sub": {"stream": "stdout", "id": "some id"}, "kubernetes": {"labels": {"team": "Santiago Wanderers"}}}
  samples   1

[OUTPUT]
  name                   loki
  match                  *
  host                   127.0.0.1
  port                   3100
  labels                 job=fluentbit
  label_keys             $sub['stream']
  auto_kubernetes_labels on

Run Fluent Bit with the corresponding new configuration file:

# For YAML configuration.
fluent-bit --config out_loki.yaml

# For classic configuration.
fluent-bit --config out_loki.conf

Which returns output that similar to the following:

...
[2020/10/14 20:57:46] [ info] [output:loki:loki.0] 127.0.0.1:3100, HTTP status=204
...

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Configuration parameters

Labels

Use label_keys

Use label_map_path

Kubernetes and labels

Use drop_single_key

Use structured_metadata

Structured metadata maps

Networking and TLS configuration

Fluent Bit and Grafana Cloud

Get started

Use `label_keys`

Use `label_map_path`

Use `drop_single_key`

Use `structured_metadata`