Substitution text if value missing

Our firewall is sending log messages to our ELK stack. Most of these messages contain a source and destination IP address.. but occasionally these values are not present. These messages are being forward via email and the values %{src} or %{dst}) are shown if these values were not in the message received.

Is there any way to either remove or replace these with a string should these values not be present in a message received.

You could delete them using

prune {}

prune can whitelist and blacklist top-level fields based on either name or value. The default configuration is to blacklist (i.e. delete) any fields for which the name matches the regexp %{[^}]+}.

If you want to overwrite them you could use

if [nameOfDstField] == "%{dst}" { mutate { replace => { "nameOfDstField" => "someValue" } } }


Thanks for your response. Would this provide the flexibility to keep the field if the value exists, but remove if it does not?

If the field exists it must have a value. What value does it have?

What I am saying is some messages use the value, some do not. When they do not I would like to put a placeholder.

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