Is it impossible to apply SSL to HEC in the Splunk trial version?
If you mean Splunk Enterprise trial, you can configure TLS on any component. If you mean Splunk Cloud trial - no. The inputs are not encrypted and the webui uses self-signed certs as far as I remember.
@kwangwon Splunkcloud trial version is a standalone system and uses self-signed certs.
You can try using curl -k "https://ilove.splunkcloud.com:8088/services/collector"
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