To add on to what magnusbaeck is saying, you cannot create an index in Elasticsearch with uppercase letters either. When trying to create an index with uppercase letters in ES, you immediately get an error stating that index was not created because it cannot contain uppercase letters.
Even if you correct this issue by changing it to lowercase in LogStash, you still must specify an index template within ES when creating an index or none of your data will be able to be used in Kibana for visualizations, meaning your data is analyzed. Only data that is not analyzed can be used for visualizations within Kibana (as annotated by the "*.raw" fields). You could modify the default index template, but it can be difficult to create a template that meets the needs of all of data you are using with Elastic Stack.
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