Use environment variable to control output

Elastic Stack Logstash
1

Hi,

From the logstash.conf, I want to control the output based on the environment variable. I have tried the following, but it does not work. I find the use of the environment variable is not consistent throughout the configuration file. Is there any good reference on this?

Thanks
Kc

output {
    ....
    if "${LS_OUTPUT_DEBUG:0}" == 1 {
        # debugging
        file {
            path => "${LOGS_DIR}/output-debug-%{+YYYYMMdd}.log"
            codec => "rubydebug"
        }
    }
2

Not that I know of. Does it help you to do this?

mutate { add_field => { "[@metadata][LS_DEBUG]" => "${LS_DEBUG:0}" "[@metadata][LOGS_DIR]" => "${LOGS_DIR}" } }
3

Hi Badger.

I don't have an issue with the LOGS_DIR. Only the LS_OUTPUT_DEBUG does not work. I support the use of environment variable for conditionals is not supported

Thanks for the suggestion. It works for the LS_OUTPUT_DEBUG now. Wondering if there is a more efficient way.

if [@metadata][LS_DEBUG] {
    # debugging
    file {
        path => "${LOGS_DIR}/restccu-debug-%{+YYYYMMdd}.log"
        codec => "rubydebug"
    }
}

Say, if I want to use an environment variable to control the filter, does it mean I will have to use mutate with add_field at the very beginning of the filter section?

4

You can use a single mutate+add_field to import everything from the environment.

5

I suppose that is the only way. Thanks again. :smile:

6

Hmm. I think I might have spoken too soon. It does not actually work. When I set the LS_OUTPUT_DEBUG=0, it still generates the output file. I am not certain what Logstash sees the value of this environment variable. Is there any way to debug the configuration file?

7

That is testing whether the field exists, which it always does.

8

Yep. I was suspecting that also so I have changed to

if [@metadata][LS_OUTPUT_DEBUG] == 1 {
...
}

Do the "export LS_OUTPUT_DEBUG=1", then start the logstash.
However, there is still no output file generated.

9

mutate+add_field never generates integers, you need to use "1" there.

10

Ouch!

11

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