The reason that you don't see any "complete solution" is that while it sounds so simple, it is actually really really complicated because of all of the different variations logs that might be observed. To explain how to do it, and I mean "do it at large scale, high throughput, highly available and in realtime" would literally mean writing a book... a thick 400 or 500 page book.
To arrive at what you are asking is a journey. You start with a one source and work to get it doing what you want. Then you add another source, and you are at the first hurdle... how to "detect" which kind of message it is and handle either format as needed. And then the vendor updates their software and message changes slightly, so you have to add in a bunch of logic to handle various "what if" scenarios. Then comes the third source, and things start to get unwieldy so you need to break it up... perhaps into multiple pipelines, maybe even multiple Logstash instances... so maybe you need Kafka to interconnect all of those instances. And the journey continues...
You could easily spend at least a year working to achieve what you so simply requested in 4 bullet points. Or you hire a consultant who can do it for you in a fraction of that time. But make sure that they can really deliver what they promise (because they already have that year+ of learning curve behind them). Unfortunately there aren't many of them out there. Either they know the Elastic Stack, and other needed technologies, but don't really understand the use-case (this is IMO what you see in many of Elastic's own modules). Or they know the use-case inside and out, but don't know enough about the Elastic Stack to make it a reality.
Either way it is a challenge... you either put in the work, or find the right help and spend some money.
Sorry. I know that isn't really the answer for which you hoped. However, I wanted to be honest with you about why you never see the answers you want.
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