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Using Environment Variables in the Configuration

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Using Environment Variables in the Configuration

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Overview

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You can set environment variable references in the configuration for Logstash plugins by using ${var}.
At Logstash startup, each reference will be replaced by the value of the environment variable.
The replacement is case-sensitive.
References to undefined variables raise a Logstash configuration error.
You can give a default value by using the form ${var:default value}. Logstash uses the default value if the environment variable is undefined.
You can add environment variable references in any plugin option type : string, number, boolean, array, or hash.
Environment variables are immutable. If you update the environment variable, you’ll have to restart Logstash to pick up the updated value.

Examples

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The following examples show you how to use environment variables to set the values of some commonly used configuration options.

Setting the TCP Port

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Here’s an example that uses an environment variable to set the TCP port:

input {
  tcp {
    port => "${TCP_PORT}"
  }
}

Now let’s set the value of TCP_PORT:

export TCP_PORT=12345

At startup, Logstash uses the following configuration:

input {
  tcp {
    port => 12345
  }
}

If the TCP_PORT environment variable is not set, Logstash returns a configuration error.

You can fix this problem by specifying a default value:

input {
  tcp {
    port => "${TCP_PORT:54321}"
  }
}

Now, instead of returning a configuration error if the variable is undefined, Logstash uses the default:

input {
  tcp {
    port => 54321
  }
}

If the environment variable is defined, Logstash uses the value specified for the variable instead of the default.

Setting the Value of a Tag

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Here’s an example that uses an environment variable to set the value of a tag:

filter {
  mutate {
    add_tag => [ "tag1", "${ENV_TAG}" ]
  }
}

Let’s set the value of ENV_TAG:

export ENV_TAG="tag2"

At startup, Logstash uses the following configuration:

filter {
  mutate {
    add_tag => [ "tag1", "tag2" ]
  }
}

Setting a File Path

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Here’s an example that uses an environment variable to set the path to a log file:

filter {
  mutate {
    add_field => {
      "my_path" => "${HOME}/file.log"
    }
  }
}

Let’s set the value of HOME:

export HOME="/path"

At startup, Logstash uses the following configuration:

filter {
  mutate {
    add_field => {
      "my_path" => "/path/file.log"
    }
  }
}

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