It's a docker image built on top of quay.io/fluentd_elasticsearch/fluentd with some additional fluentd plugin's installed
3.3.0,latest(v3.3.0/Dockerfile)2.7.1(v2.7.1/Dockerfile)2.7.0(v2.7.0/Dockerfile)2.6.0(v2.6.0/Dockerfile)2.5.2(v2.5.2/Dockerfile)2.3.1(v2.3.1/Dockerfile)
The source code of used base image is here: https://github.com/kubernetes/kubernetes/tree/master/cluster/addons/fluentd-elasticsearch/fluentd-es-image. At the moment, the base image is prepared manually from the mentioned repository by the kubernetes team. The fluentd version is specified in Gemfile, now it is v1.12.0 The fluentd last build is v1.13.3
The cloudwatch-logs plugin allows to transfer logs to Amazon CloudWatch. Plugin source code: https://github.com/fluent-plugins-nursery/fluent-plugin-cloudwatch-logs/tree/v0.14.0
The rabbitmq plugin is used in Kublr to delivery logs from the cluster to the Centralized Logging ELK. Plugin source code: https://github.com/nttcom/fluent-plugin-rabbitmq/tree/v0.0.9
The fluent-plugin-remote_syslog plugin for output to remote syslog service. Plugin source code: https://github.com/dlackty/fluent-plugin-remote_syslog/tree/v1.0.0
For more details refer to https://github.com/kubernetes/kubernetes/tree/master/cluster/addons/fluentd-elasticsearch/fluentd-es-image