I follow the steps given in above link for install app in distributed environment, I installed "Splunk Add on for AWS".
I have 2 search head servers, but using above link its come only on single Search Head, I verified from the back-end.
Is this any fault in my environment setups ? Or I need to copy the same app using linux command to the other Search Head server ?
Or only one env its OK??
There are several sets of instructions at that link and you didn't say which one you followed. The instructions for a single search head put the app only on that search head. You'll have to repeat the steps for the other SH (unless they're clustered or under a deployment server, but neither was mentioned so I'll assume they don't apply).
Don't forget to install the add-on on your indexers. That's also a separate step.
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