Important: This documentation is about an older version. It's relevant only to the release noted, many of the features and functions have been updated or replaced. Please view the current version.

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Logstash plugin

Open source

Logstash plugin

Grafana Loki has a Logstash output plugin called logstash-output-loki that enables shipping logs to a Loki instance or Grafana Cloud.

Installation

Local

If you need to install the Logstash output plugin manually you can do simply so by using the command below:

$ bin/logstash-plugin install logstash-output-loki

This will download the latest gem for the output plugin and install it in logstash.

Docker

We also provide a docker image on docker hub. The image contains logstash and the Loki output plugin already pre-installed.

For example if you want to run logstash in docker with the loki.conf as pipeline configuration you can use the command bellow :

docker run -v `pwd`/loki-test.conf:/home/logstash/ --rm grafana/logstash-output-loki:1.0.1 -f loki-test.conf

Kubernetes

We also provide default helm values for scraping logs with Filebeat and forward them to Loki with logstash in our loki-stack umbrella chart. You can switch from Promtail to logstash by using the following command:

helm upgrade --install loki loki/loki-stack \
    --set filebeat.enabled=true,logstash.enabled=true,promtail.enabled=false \
    --set loki.fullnameOverride=loki,logstash.fullnameOverride=logstash-loki

This will automatically scrape all pods logs in the cluster and send them to Loki with Kubernetes metadata attached as labels. You can use the values.yaml file as a starting point for your own configuration.

Usage and Configuration

To configure Logstash to forward logs to Loki, simply add the loki output to your Logstash configuration file as documented below :

output {
  loki {
    [url => "" | default = none | required=true]

    [tenant_id => string | default = nil | required=false]

    [message_field => string | default = "message" | required=false]
    
    [include_fields => array | default = [] | required=false]

    [batch_wait => number | default = 1(s) | required=false]

    [batch_size => number | default = 102400(bytes) | required=false]

    [min_delay => number | default = 1(s) | required=false]

    [max_delay => number | default = 300(s) | required=false]

    [retries => number | default = 10 | required=false]

    [username => string | default = nil | required=false]

    [password => secret | default = nil | required=false]

    [cert => path | default = nil | required=false]

    [key => path | default = nil| required=false]

    [ca_cert => path | default = nil | required=false]

    [insecure_skip_verify => boolean | default = false | required=false]
  }
}

By default Loki will create entry from event fields it receives. A logstash event as shown below.

{
  "@timestamp" => 2017-04-26T19:33:39.257Z,
  "src"        => "localhost",
  "@version"   => "1",
  "host"       => "localhost.localdomain",
  "pid"        => "1",
  "message"    => "Apr 26 12:20:02 localhost systemd[1]: Starting system activity accounting tool...",
  "type"       => "stdin",
  "prog"       => "systemd",
}

Contains a message and @timestamp fields, which are respectively used to form the Loki entry log line and timestamp.

You can use a different property for the log line by using the configuration property message_field. If you also need to change the timestamp value use the Logstash date filter to change the @timestamp field.

All other fields (except nested fields) will form the label set (key value pairs) attached to the log line. This means you’re responsible for mutating and dropping high cardinality labels such as client IPs. You can usually do so by using a mutate filter.

Note: In version 1.1.0 and greater of this plugin you can also specify a list of labels to allowlist via the include_fields configuration.

For example the configuration below :

input {
  ...
}

filter {
  mutate {
    add_field => {
      "cluster" => "us-central1"
      "job" => "logstash"
    }
    replace => { "type" => "stream"}
    remove_field => ["src"]
  }
}
output {
  loki {
    url => "http://myloki.domain:3100/loki/api/v1/push"
  }
}

Will add cluster and job static labels, remove src fields and replace type to be named stream.

If you want to include nested fields or metadata fields (starting with @) you need to rename them.

For example when using Filebeat with the add_kubernetes_metadata processor, it will attach Kubernetes metadata to your events like below:

{
  "kubernetes" : {
    "labels" : {
      "app" : "MY-APP",
      "pod-template-hash" : "959f54cd",
      "serving" : "true",
      "version" : "1.0",
      "visualize" : "true"
    },
    "pod" : {
      "uid" : "e20173cb-3c5f-11ea-836e-02c1ee65b375",
      "name" : "MY-APP-959f54cd-lhd5p"
    },
    "node" : {
      "name" : "ip-xxx-xx-xx-xxx.ec2.internal"
    },
    "container" : {
      "name" : "istio"
    },
    "namespace" : "production",
    "replicaset" : {
      "name" : "MY-APP-959f54cd"
    }
  },
  "message": "Failed to parse configuration",
  "@timestamp": "2017-04-26T19:33:39.257Z",
}

The filter below show you how to extract those Kubernetes fields into labels (container_name,namespace,pod and host):

filter {
  if [kubernetes] {
    mutate {
      add_field => {
        "container_name" => "%{[kubernetes][container][name]}"
        "namespace" => "%{[kubernetes][namespace]}"
        "pod" => "%{[kubernetes][pod][name]}"
      }
      replace => { "host" => "%{[kubernetes][node][name]}"}
    }
  }
  mutate {
    remove_field => ["tags"]
  }
}

Configuration Properties

url

The url of the Loki server to send logs to. When sending data the push path need to also be provided e.g. http://localhost:3100/loki/api/v1/push.

If you want to send to GrafanaCloud you would use https://logs-prod-us-central1.grafana.net/loki/api/v1/push.

username / password

Specify a username and password if the Loki server requires basic authentication. If using the GrafanaLab’s hosted Loki, the username needs to be set to your instance/user id and the password should be a Grafana.com api key.

message_field

Message field to use for log lines. You can use logstash key accessor language to grab nested property, for example : [log][message].

include_fields

An array of fields which will be mapped to labels and sent to Loki, when this list is configured only these fields will be sent, all other fields will be ignored.

batch_wait

Interval in seconds to wait before pushing a batch of records to Loki. This means even if the batch size is not reached after batch_wait a partial batch will be sent, this is to ensure freshness of the data.

batch_size

Maximum batch size to accrue before pushing to loki. Defaults to 102400 bytes

Backoff config

min_delay => 1(1s)

Initial backoff time between retries

max_delay => 300(5m)

Maximum backoff time between retries

retries => 10

Maximum number of retries to do. Setting it to 0 will retry indefinitely.

tenant_id

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.

insecure_skip_verify

A flag to disable server certificate verification. By default it is set to false.

Full configuration example

input {
  beats {
    port => 5044
  }
}

filter {
  if [kubernetes] {
    mutate {
      add_field => {
        "container_name" => "%{[kubernetes][container][name]}"
        "namespace" => "%{[kubernetes][namespace]}"
        "pod" => "%{[kubernetes][pod][name]}"
      }
      replace => { "host" => "%{[kubernetes][node][name]}"}
    }
  }
  mutate {
    remove_field => ["tags"]  # Note: with include_fields defined below this wouldn't be necessary
  }
}

output {
  loki {
    url => "https://logs-prod-us-central1.grafana.net/loki/api/v1/push"
    username => "3241"
    password => "REDACTED"
    batch_size => 112640 #112.64 kilobytes
    retries => 5
    min_delay => 3
    max_delay => 500
    message_field => "message"
    include_fields => ["container_name","namespace","pod","host"]
  }
  # stdout { codec => rubydebug }
}