How to configure ELK (Elasticsearch, Logstash,Kibana) for different application log files and display each application separately in Kibana?

Elastic Stack Logstash
12

is this my else condition which cause logstash-* index ?

It sounds like you effectively have this:

output {
  if [type] == "OnsuranceAppLog" {
    elasticsearch { 
      hosts => ["localhost:9200"] 
      index => "onsurance-%{+YYYY.MM.dd}"
    }
  } else {
    elasticsearch {
      hosts => ["localhost:9200"]
    }
    stdout { codec => rubydebug }
  }
  if [type] == "iis" {
    elasticsearch { 
      hosts => ["localhost:9200"] 
      index => "iis-%{+YYYY.MM.dd}"
    }
  } else {
    elasticsearch {
      hosts => ["localhost:9200"]
    }
    stdout { codec => rubydebug }
  }
}

In that case yes, the else block is the problem. All messages will reach it.

another question is, how can i tell ES to keep index of only last 30 days? and delete everything which is older than 30 days. I know you can fire a query to ES but is there any Setting which i can set once and it does the magic?

There's no setting but the Curator program can do this for you.