Configuration Variables
Fluent Bit support the usage of environment variables in any value associated to a key when using a configuration file.
The variables are case sensitive and can be used in the following format:
${MY_VARIABLE}
When Fluent Bit starts, the configuration reader will detect any request for ${MY_VARIABLE} and will try to resolve it value.

Example

Create the following configuration file (fluent-bit.conf):
[SERVICE]
Flush 1
Daemon Off
Log_Level info
[INPUT]
Name cpu
Tag cpu.local
[OUTPUT]
Name ${MY_OUTPUT}
Match *
Open a terminal and set the environment variable:
$ export MY_OUTPUT=stdout
The above command set the 'stdout' value to the variable MY_OUTPUT.
Run Fluent Bit with the recently created configuration file:
$ bin/fluent-bit -c fluent-bit.conf
Fluent-Bit v0.11.0
Copyright (C) Treasure Data
[2017/04/03 12:25:25] [ info] [engine] started
[0] cpu.local: [1491243925, {"cpu_p"=>1.750000, "user_p"=>1.750000, "system_p"=>0.000000, "cpu0.p_cpu"=>3.000000, "cpu0.p_user"=>2.000000, "cpu0.p_system"=>1.000000, "cpu1.p_cpu"=>0.000000, "cpu1.p_user"=>0.000000, "cpu1.p_system"=>0.000000, "cpu2.p_cpu"=>4.000000, "cpu2.p_user"=>4.000000, "cpu2.p_system"=>0.000000, "cpu3.p_cpu"=>1.000000, "cpu3.p_user"=>1.000000, "cpu3.p_system"=>0.000000}]
As you can see the service worked properly as the configuration was valid.
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