Multiple pipelines or tags or if or else if?

Elastic Stack Logstash
2

Not sure which of those issues you want to address, but I will assume you want to send different types of data to different indexes based on tags. There are two approaches. One is to use conditionals in the output section.

output { 
    if "somestring" in [tags] {
        elasticsearch { "index" => "Foo" }
    } else if "otherstring" in [tags] {
        elasticsearch { "index" => "Bar" }
    } else {
        elasticsearch { "index" => "Baz" }
    }
}

Another is to use conditionals to put the index name into a field

filter {
    if "somestring" in [tags] {
         mutate { add_field => { "[@metadata][indexPrefix]" => "Foo" } }
    } else if "otherstring" in [tags] {
         mutate { add_field => { "[@metadata][indexPrefix]" => "Bar" } }
    } else {
         mutate { add_field => { "[@metadata][indexPrefix]" => "Baz" } }
    }
}
output {
    elasticsearch { index => "%{[@metadata][indexPrefix]}-%{+YYYY.MM}" }
}