Suggestion on Logstash Setup - logstash

Question

I've implemented logstash ( in testing ) as below mentioned architecture.
Component Break Down
Rsyslog client: By default syslog installed in all Linux destros, we just need to configure rsyslog to send logs to remote server.
Logstash: Logstash will received logs from syslog client and it will
store in Redis.
Redis: Redis will work as broker, broker is to hold log data sent by agents before logstash indexes it. Having a broker will enhance performance of the logstash server, Redis acts like a buffer for log data, till logstash indexes it and stores it. As it is in RAM its too fast.
Logstash: yes, two instance of logstash, 1st one for syslog server,
2nd for read data from redis and send out to elasticsearch.
Elasticsearch: The main objective of a central log server is to collect all logs at one place, plus it should provide some meaningful data for analysis. Like you should be able to search all log data for your particular application at a specified time period.Hence there must be a searching and well indexing capability on our logstash server. To achieve this, we will install another opensource tool called as elasticsearch.Elasticsearch uses a mechanism of making an index, and then search that index to make it faster. Its a kind of search engine for text data.
Kibana : Kibana is a user friendly way to view, search and visualize
your log data
But I'm little bit confuse with redis. using this scenario I'll be running 3 java process on Logstash server and one redis, this will take hugh ram.
Question
Can I use only one logstash and elastic search ? Or what would be the best way ?

Answer 1

I am actually in the midst of setting up logstash, redis, elasticsearch, kibana (aka ELK architecture) at my company.
I have the processes split between virtual machines. While you could put them on the same machine, what happens if a machine dies? Then you are left with your indexer and cluster down at the same time.
You also have the problem of not being able to properly replicate your shards on the Elasticsearch. Since you only have one server, the shards won't be replicated and your cluster health will always be yellow. You need to add enough servers to avoid the split-brain scenario.
Why keep Redis?
Since Redis can talk to multiple logstash indexers, one key point is that this makes the indexing transparent to your shippers in that if one indexer goes down, the alternates will pick up the load. This makes your setup high availability.
It's not just a matter of shipping logs and having them indexed and searchable. While your setup will likely work in a very small, rare situation, the stuff people are doing with ELK setups are hundreds of servers, even thousands, so the ELK architecture is meant to scale. All of these servers will also need to be remotely managed by something called Puppet.
Finally, if you have not read it yet, I suggest you read The Logstash Book by James Turnbull.
The following are some more recommended books that have helped me so far:
Pro Puppet, Second Edition
Elasticsearch Cookbook, Second Edition
Redis Cookbook
Redis in Action
Mastering Elasticsearch
ElasticSearch Server
Elasticsearch: The Definitive Guide
Puppet Types and Providers
Puppet 3 Cookbook

Answer 2

You can use only one logstash and elasticsearch if you put all the instance in a machine. Logstash directly read the syslog file by using file input plugin.
Otherwise, you have to use two logstash and redis. It is because logstash do not have any buffer mechanism, so it needs redis as its broker to buffer the log event. Redis do not use more ram. When logstash read the log event from it, the memory will release. If redis use large ram, you have to add the logstash workers for processing the logs faster.

Answer 3

You should only be running one instance of logstash. logstash by design has the ability to have multiple input channels and output channels.
input {
# input instances
syslog {
# add other settings accordingly
type => "syslog"
}
redis {
# add other settings accordingly
type => "redis"
}
}
filter {
# add other settings accordingly
}
output {
# output instances
if [type] == "syslog" {
redis {
# add other settings accordingly
}
}
else if [type] == "redis" {
elasticsearch {
# add other settings accordingly
}
}
}