I worked with http output from fluentd and http input for logstash, below the configuration fragments:
fluentd:
<match **> @type http endpoint_url http://logstash-box:8080/ http_method put serializer json raise_on_error false </match>
Logstash:
input { http { port => 8080 } }
Discussion: You may need to install the gem install fluent-plugin-out-http
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