A minimalistic adapter for github.com/gliderlabs/logspout to write to Logstash
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logspout-logstash

A minimalistic adapter for github.com/gliderlabs/logspout to write to Logstash

Follow the instructions in https://github.com/gliderlabs/logspout/tree/master/custom on how to build your own Logspout container with custom modules. Basically just copy the contents of the custom folder and include:

package main

import (
  _ "github.com/looplab/logspout-logstash"
  _ "github.com/gliderlabs/logspout/transports/udp"
  _ "github.com/gliderlabs/logspout/transports/tcp"
)

in modules.go.

Use by setting a docker environment variable ROUTE_URIS=logstash://host:port to the Logstash server. The default protocol is UDP, but it is possible to change to TCP by adding +tcp after the logstash protocol when starting your container.

docker run --name="logspout" \
    --volume=/var/run/docker.sock:/var/run/docker.sock \
    -e ROUTE_URIS=logstash+tcp://logstash.home.local:5000 \
    localhost/logspout-logstash:v3.1

In your logstash config, set the input codec to json e.g:

input {
  udp {
    port  => 5000
    codec => json
  }
  tcp {
    port  => 5000
    codec => json
  }
}

Available configuration options

For example, to get into the Logstash event's @tags field, use the LOGSTASH_TAGS container environment variable. Multiple tags can be passed by using comma-separated values

  # Add any number of arbitrary tags to your event
  -e LOGSTASH_TAGS="docker,production"

The output into logstash should be like:

    "tags": [
      "docker",
      "production"
    ],

You can also add arbitrary logstash fields to the event using the LOGSTASH_FIELDS container environment variable:

  # Add any number of arbitrary fields to your event
  -e LOGSTASH_FIELDS="myfield=something,anotherfield=something_else"

The output into logstash should be like:

    "myfield": "something",
    "another_field": "something_else",

Both configuration options can be set for every individual container, or for the logspout-logstash container itself where they then become a default for all containers if not overridden there.

By setting the environment variable DOCKER_LABELS to a non-empty value, logspout-logstash will add all docker container labels as fields:

    "docker": {
        "hostname": "866e2ca94f5f",
        "id": "866e2ca94f5fe11d57add5a78232c53dfb6187f04f6e150ec15f0ae1e1737731",
        "image": "centos:7",
        "labels": {
            "a_label": "yes",
            "build-date": "20161214",
            "license": "GPLv2",
            "name": "CentOS Base Image",
            "pleasework": "okay",
            "some_label_with_dots": "more.dots",
            "vendor": "CentOS"
        },
        "name": "/ecstatic_murdock"

To be compatible with Elasticsearch, dots in labels will be replaced with underscores.

Retrying

Two environment variables control the behaviour of Logspout when the Logstash target isn't available: RETRY_STARTUP causes Logspout to retry forever if Logstash isn't available at startup, and RETRY_SEND will retry sending log lines when Logstash becomes unavailable while Logspout is running. Note that RETRY_SEND will work only if UDP is used for the log transport and the destination doesn't change; in any other case RETRY_SEND should be disabled, restart and reconnect instead and let RETRY_STARTUP deal with the situation. With both retry options, log lines will be lost when Logstash isn't available. Set the environment variables to any nonempty value to enable retrying. The default is disabled.

This table shows all available configurations:

Environment Variable Input Type Default Value
LOGSTASH_TAGS array None
LOGSTASH_FIELDS map None
DOCKER_LABELS any ""
RETRY_STARTUP any ""
RETRY_SEND any ""
DECODE_JSON_LOGS bool true