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 literal ${ in your configuration file then you can write $${ to escape the expansion.

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

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

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.