Map ruby hash to logstash configuration file - ruby

Question

I have the following ruby hash.
config = {
'output' => {
'elasticsearch' => {
'hosts' => ['localhost:9200']
}
}
}
Which I'm trying to represent as a logstash configuration file (https://www.elastic.co/guide/en/logstash/current/configuration.html). In this case, something that looks similar to this.
output {
elasticsearch { hosts => ["localhost:9200"] }
}
I've tried using map which is close, but "elasticsearch" should not have "=>" and "elasticsearch" and "hosts" should not be quoted.
puts config.map{|k, v| "#{k} #{v}"}.join('&')
output {"elasticsearch"=>{"hosts"=>["localhost:9200"]}}
I've also tried converting to json and using gsub, but in this case I need to unindent the string and "output" and "elasticsearch" should not be quoted.
puts JSON.pretty_generate(config).gsub(/^[{}]$/, "")
.gsub(": {", " {")
.gsub(": ", " => ")[1..-2]
"output" {
"elasticsearch" {
"hosts" => [
"localhost:9200"
]
}
}
While each implementation is close, it's still off by a bit. Is there a simple way to achieve this?

Answer 1

The Logstash config format isn't standard JSON or anything. It may be best to just write a serializer for it. I took a quick stab at it:
def serialize_config(config, tabs = 0)
clauses = []
config.each do |key, val|
case val
when Hash
clauses << format("%s {\n%s%s}", key, serialize_config(val, tabs + 1), "\t" * tabs)
else
clauses << format("%s => %s", key, val.inspect)
end
end
clauses.map {|c| format("%s%s\n", "\t" * tabs, c) }.join
end
config = {
'output' => {
'elasticsearch' => {
'hosts' => ['localhost:9200']
},
'ruby' => {
"code" => "event.cancel if rand <= 0.90"
}
}
}
puts serialize_config(config)
When gives output:
output {
elasticsearch {
hosts => ["localhost:9200"]
}
ruby {
code => "event.cancel if rand <= 0.90"
}
}
You'd want to check it against more complex Logstash configs, though.