Environment variables

You can use environment variable references in the config file to set values that need to be configurable during deployment. To do this, use:

${VAR}

Where VAR is the name of the environment variable.

Each variable reference is replaced at startup by the value of the environment variable. The replacement is case-sensitive and occurs before the YAML file is parsed. References to undefined variables are replaced by empty strings unless you specify a default value or custom error text.

To specify a default value, use:

${VAR:default_value}

Where default_value is the value to use if the environment variable is undefined.

To specify custom error text, use:

${VAR:?error_text}

Where error_text is custom text that will be prepended to the error message if the environment variable cannot be expanded.

If you need to use a special character in your configuration file, use $ to escape the expansion. For example, you can escape ${ or } with $${ or $}.

After changing the value of an environment variable, you need to restart a Beat to pick up the new value.

You can also specify environment variables when you override a config setting from the command line by using the -E option. For example:

-E name=${NAME}

Examples

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Here are some examples of configurations that use environment variables and what each configuration looks like after replacement:

Config source	Environment setting	Config after replacement
`name: ${NAME}`	`export NAME=elastic`	`name: elastic`
`name: ${NAME}`	no setting	`name:`
`name: ${NAME:beats}`	no setting	`name: beats`
`name: ${NAME:beats}`	`export NAME=elastic`	`name: elastic`
`name: ${NAME:?You need to set the NAME environment variable}`	no setting	None. Returns an error message that’s prepended with the custom text.
`name: ${NAME:?You need to set the NAME environment variable}`	`export NAME=elastic`	`name: elastic`

Specify complex objects in environment variables

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You can specify complex objects, such as lists or dictionaries, in environment variables by using a JSON-like syntax.

As with JSON, dictionaries and lists are constructed using {} and []. But unlike JSON, the syntax allows for trailing commas and slightly different string quotation rules. Strings can be unquoted, single-quoted, or double-quoted, as a convenience for simple settings and to make it easier for you to mix quotation usage in the shell. Arrays at the top-level do not require brackets ([]).

For example, the following environment variable is set to a list:

ES_HOSTS="10.45.3.2:9220,10.45.3.1:9230"

You can reference this variable in the config file:

output.elasticsearch:
  hosts: '${ES_HOSTS}'

When a Beat loads the config file, it resolves the environment variable and replaces it with the specified list before reading the hosts setting.

Do not use double-quotes (") to wrap regular expressions, or the backslash (\) will be interpreted as an escape character.

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