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Ingesting logs to Loki using OpenTelemetry Collector

Loki natively supports ingesting OpenTelemetry logs over HTTP. For ingesting logs to Loki using the OpenTelemetry Collector, you must use the otlphttp exporter.

Loki configuration

When logs are ingested by Loki using an OpenTelemetry protocol (OTLP) ingestion endpoint, some of the data is stored as Structured Metadata.

You must set allow_structured_metadata to true within your Loki config file. Otherwise, Loki will reject the log payload as malformed.

yaml 
limits_config:
  allow_structured_metadata: true

Configure the OpenTelemetry Collector to write logs into Loki

You need to make the following changes to the OpenTelemetry Collector config to write logs to Loki on its OTLP ingestion endpoint.

yaml 
exporters:
  otlphttp:
    endpoint: http://<loki-addr>:3100/otlp

And enable it in service.pipelines:

yaml 
service:
  pipelines:
    logs:
      receivers: [...]
      processors: [...]
      exporters: [..., otlphttp]

If you want to authenticate using basic auth, we recommend the basicauth extension.

yaml 
extensions:
  basicauth/otlp:
    client_auth:
      username: username
      password: password

exporters:
  otlphttp:
    auth:
      authenticator: basicauth/otlp
    endpoint: http://<loki-addr>:3100/otlp

service:
  extensions: [basicauth/otlp]
  pipelines:
    logs:
      receivers: [...]
      processors: [...]
      exporters: [..., otlphttp]

Format considerations

Since the OpenTelemetry protocol differs from the Loki storage model, here is how data in the OpenTelemetry format will be mapped by default to the Loki data model during ingestion, which can be changed as explained later:

  • Index labels: Resource attributes map well to index labels in Loki, since both usually identify the source of the logs. The default list of Resource Attributes to store as Index labels can be configured using default_resource_attributes_as_index_labels under distributor’s otlp_config. By default, the following resource attributes will be stored as index labels, while the remaining attributes are stored as Structured Metadata with each log entry:

    • cloud.availability_zone

    • cloud.region

    • container.name

    • deployment.environment

    • k8s.cluster.name

    • k8s.container.name

    • k8s.cronjob.name

    • k8s.daemonset.name

    • k8s.deployment.name

    • k8s.job.name

    • k8s.namespace.name

    • k8s.pod.name

    • k8s.replicaset.name

    • k8s.statefulset.name

    • service.instance.id

    • service.name

    • service.namespace

      Note

      Because Loki has a default limit of 15 index labels, we recommend storing only select resource attributes as index labels. Although the default config selects more than 15 Resource Attributes, it should be fine since a few are mutually exclusive.

  • Timestamp: One of LogRecord.TimeUnixNano or LogRecord.ObservedTimestamp, based on which one is set. If both are not set, the ingestion timestamp will be used.

  • LogLine: LogRecord.Body holds the body of the log. However, since Loki only supports Log body in string format, we will stringify non-string values using the AsString method from the OTel collector lib.

  • Structured Metadata: Anything which can’t be stored in Index labels and LogLine would be stored as Structured Metadata. Here is a non-exhaustive list of what will be stored in Structured Metadata to give a sense of what it will hold:

    • Resource Attributes not stored as Index labels is replicated and stored with each log entry.
    • Everything under InstrumentationScope is replicated and stored with each log entry.
    • Everything under LogRecord except LogRecord.Body, LogRecord.TimeUnixNano and sometimes LogRecord.ObservedTimestamp.

Things to note before ingesting OpenTelemetry logs to Loki:

  • Dots (.) are converted to underscores (_).

    Loki does not support . or any other special characters other than _ in label names. The unsupported characters are replaced with an _ while converting Attributes to Index Labels or Structured Metadata. Also, please note that while writing the queries, you must use the normalized format, i.e. use _ instead of special characters while querying data using OTel Attributes.

    For example, service.name in OTLP would become service_name in Loki.

  • Flattening of nested Attributes

    While converting Attributes in OTLP to Index labels or Structured Metadata, any nested attribute values are flattened out using _ as a separator. It is done in a similar way as to how it is done in the LogQL json parser.

  • Stringification of non-string Attribute values

    While converting Attribute values in OTLP to Index label values or Structured Metadata, any non-string values are converted to string using AsString method from the OTel collector lib.

Changing the default mapping of OTLP to Loki Format

Loki supports per tenant OTLP config which lets you change the default mapping of OTLP to Loki format for each tenant. It currently only supports changing the storage of Attributes. Here is how the config looks like:

yaml 
# OTLP log ingestion configurations
limits_config:
  otlp_config:
    # Configuration for Resource Attributes to store them as index labels or
    # Structured Metadata or drop them altogether
    resource_attributes:
      # Configure whether to ignore the default list of resource attributes set in
      # 'distributor.otlp.default_resource_attributes_as_index_labels' to be
      # stored as index labels and only use the given resource attributes config
      [ignore_defaults: <boolean>]
  
      [attributes_config: <list of attributes_configs>]
  
    # Configuration for Scope Attributes to store them as Structured Metadata or
    # drop them altogether
    [scope_attributes: <list of attributes_configs>]
  
    # Configuration for Log Attributes to store them as Structured Metadata or
    # drop them altogether
    [log_attributes: <list of attributes_configs>]
  
  attributes_config:
    # Configures action to take on matching Attributes. It allows one of
    # [structured_metadata, drop] for all Attribute types. It additionally allows
    # index_label action for Resource Attributes
    [action: <string> | default = ""]
  
    # List of attributes to configure how to store them or drop them altogether
    [attributes: <list of strings>]
  
    # Regex to choose attributes to configure how to store them or drop them
    # altogether
    [regex: <Regexp>]

Here are some example configs to change the default mapping of OTLP to Loki format:

Example 1:

yaml 
limits_config:
  otlp_config:
    resource_attributes:
      attributes_config:
        - action: index_label
          attributes:
            - service.group

With the example config, here is how various kinds of Attributes would be stored:

  • Store all 17 Resource Attributes mentioned earlier and service.group Resource Attribute as index labels.
  • Store remaining Resource Attributes as Structured Metadata.
  • Store all the Scope and Log Attributes as Structured Metadata.

Example 2:

yaml 
limits_config:
  otlp_config:
    resource_attributes:
      ignore_defaults: true
      attributes_config:
        - action: index_label
          regex: service.group

With the example config, here is how various kinds of Attributes would be stored:

  • Only store service.group Resource Attribute as index labels.
  • Store remaining Resource Attributes as Structured Metadata.
  • Store all the Scope and Log Attributes as Structured Metadata.

Example 3:

yaml 
limits_config:
  otlp_config:
    resource_attributes:
      attributes_config:
        - action: index_label
          regex: service.group
    scope_attributes:
      - action: drop
        attributes:
          - method.name
    log_attributes:
      - action: structured_metadata
        attributes:
          - user.id
      - action: drop
        regex: .*

With the example config, here is how various kinds of Attributes would be stored:

  • Store all 17 Resource Attributes mentioned earlier and service.group Resource Attribute as index labels.
  • Store remaining Resource Attributes as Structured Metadata.
  • Drop Scope Attribute named method.name and store all other Scope Attributes as Structured Metadata.
  • Store Log Attribute named user.id as Structured Metadata and drop all other Log Attributes.