Enrich your fluentd events with Kubernetes metadata


fluent-plugin-kubernetes_metadata_filter, a plugin for Fluentd

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The Kubernetes metadata plugin filter enriches container log records with pod and namespace metadata.

This plugin derives basic metadata about the container that emitted a given log record using the source of the log record. Records from journald provide metadata about the container environment as named fields. Records from JSON files encode metadata about the container in the file name. The initial metadata derived from the source is used to lookup additional metadata about the container's associated pod and namespace (e.g. UUIDs, labels, annotations) when the kubernetes_url is configured. If the plugin cannot authoritatively determine the namespace of the container emitting a log record, it will use an 'orphan' namespace ID in the metadata. This behaviors supports multi-tenant systems that rely on the authenticity of the namespace for proper log isolation.


fluent-plugin-kubernetes_metadata_filter fluentd ruby
>= 2.0.0 >= v0.14.20 >= 2.1
< 2.0.0 >= v0.12.0 >= 1.9

NOTE: For v0.12 version, you should use 1.x.y version. Please send patch into v0.12 branch if you encountered 1.x version's bug.

NOTE: This documentation is for fluent-plugin-kubernetes_metadata_filter-plugin-elasticsearch 2.x or later. For 1.x documentation, please see v0.12 branch.


gem install fluent-plugin-kubernetes_metadata_filter


Configuration options for fluent.conf are:

  • kubernetes_url - URL to the API server. Set this to retrieve further kubernetes metadata for logs from kubernetes API server. If not specified, environment variables KUBERNETES_SERVICE_HOST and KUBERNETES_SERVICE_PORT will be used if both are present which is typically true when running fluentd in a pod.
  • apiVersion - API version to use (default: v1)
  • ca_file - path to CA file for Kubernetes server certificate validation
  • verify_ssl - validate SSL certificates (default: true)
  • client_cert - path to a client cert file to authenticate to the API server
  • client_key - path to a client key file to authenticate to the API server
  • bearer_token_file - path to a file containing the bearer token to use for authentication
  • tag_to_kubernetes_name_regexp - the regular expression used to extract kubernetes metadata (pod name, container name, namespace) from the current fluentd tag. This must used named capture groups for container_name, pod_name & namespace (default: \.(?<pod_name>[^\._]+)_(?<namespace>[^_]+)_(?<container_name>.+)-(?<docker_id>[a-z0-9]{64})\.log$</pod>))
  • cache_size - size of the cache of Kubernetes metadata to reduce requests to the API server (default: 1000)
  • cache_ttl - TTL in seconds of each cached element. Set to negative value to disable TTL eviction (default: 3600 - 1 hour)
  • watch - set up a watch on pods on the API server for updates to metadata (default: true)
  • de_dot - replace dots in labels and annotations with configured de_dot_separator, required for ElasticSearch 2.x compatibility (default: true)
  • de_dot_separator - separator to use if de_dot is enabled (default: _)
  • use_journal - If false (default), messages are expected to be formatted and tagged as if read by the fluentd in_tail plugin with wildcard filename. If true, messages are expected to be formatted as if read from the systemd journal. The MESSAGE field has the full message. The CONTAINER_NAME field has the encoded k8s metadata (see below). The CONTAINER_ID_FULL field has the full container uuid. This requires docker to use the --log-driver=journald log driver.
  • container_name_to_kubernetes_regexp - The regular expression used to extract the k8s metadata encoded in the journal CONTAINER_NAME field (default: '^(?<name_prefix>[^_]+)_(?<container_name>[^\._]+)(\.(?<container_hash>[^_]+))?_(?<pod_name>[^_]+)_(?<namespace>[^_]+)_[^_]+_[^_]+$'
  • annotation_match - Array of regular expressions matching annotation field names. Matched annotations are added to a log record.
  • allow_orphans - Modify the namespace and namespace id to the values of orphaned_namespace_name and orphaned_namespace_id when true (default: true)
  • orphaned_namespace_name - The namespace to associate with records where the namespace can not be determined (default: .orphaned)
  • orphaned_namespace_id - The namespace id to associate with records where the namespace can not be determined (default: orphaned)

NOTE: As of the release 2.1.x of this plugin, it no longer supports parsing the source message into JSON and attaching it to the payload. The following configuration options are removed:

  • merge_json_log
  • preserve_json_log

Reading from the JSON formatted log files with in_tail and wildcard filenames:

  type tail
  path /var/log/containers/*.log
  pos_file fluentd-docker.pos
  time_format %Y-%m-%dT%H:%M:%S
  tag kubernetes.*
  format json
  read_from_head true

<filter kubernetes.var.log.containers.**.log>
  type kubernetes_metadata

<match **>
  type stdout

Reading from the systemd journal (requires the fluentd fluent-plugin-systemd and systemd-journal plugins, and requires docker to use the --log-driver=journald log driver):

  type systemd
  path /run/log/journal
  pos_file journal.pos
  tag journal
  read_from_head true

# probably want to use something like fluent-plugin-rewrite-tag-filter to
# retag entries from k8s
<match journal>
  @type rewrite_tag_filter
  rewriterule1 CONTAINER_NAME ^k8s_ kubernetes.journal.container

<filter kubernetes.**>
  type kubernetes_metadata
  use_journal true

<match **>
  type stdout

Environment variables for Kubernetes

If the name of the Kubernetes node the plugin is running on is set as an environment variable with the name K8S_NODE_NAME, it will reduce cache misses and needless calls to the Kubernetes API.

In the Kubernetes container definition, this is easily accomplished by:

- name: K8S_NODE_NAME
      fieldPath: spec.nodeName

Example input/output

Kubernetes creates symlinks to Docker log files in /var/log/containers/*.log. Docker logs in JSON format.

Assuming following inputs are coming from a log file named /var/log/containers/fabric8-console-controller-98rqc_default_fabric8-console-container-df14e0d5ae4c07284fa636d739c8fc2e6b52bc344658de7d3f08c36a2e804115.log:

  "log": "2015/05/05 19:54:41 \n",
  "stream": "stderr",
  "time": "2015-05-05T19:54:41.240447294Z"

Then output becomes as belows

  "log": "2015/05/05 19:54:41 \n",
  "stream": "stderr",
  "docker": {
    "id": "df14e0d5ae4c07284fa636d739c8fc2e6b52bc344658de7d3f08c36a2e804115",
  "kubernetes": {
    "host": "jimmi-redhat.localnet",
    "pod_id": "c76927af-f563-11e4-b32d-54ee7527188d",
    "container_name": "fabric8-console-container",
    "namespace_name": "default",
    "namespace_id": "23437884-8e08-4d95-850b-e94378c9b2fd",
    "namespace_annotations": {
      "fabric8.io/git-commit": "5e1116f63df0bac2a80bdae2ebdc563577bbdf3c"
    "namespace_labels": {
      "product_version": "v1.0.0"
    "labels": {
      "component": "fabric8Console"

If using journal input, from docker configured with --log-driver=journald, the input looks like the journalctl -o export format:

# The stream identification is encoded into the PRIORITY field as an
# integer: 6, or github.com/coreos/go-systemd/journal.Info, marks stdout,
# while 3, or github.com/coreos/go-systemd/journal.Err, marks stderr.
MESSAGE= - - [21/May/2016:16:52:05 +0000] "GET /healthz HTTP/1.1" 200 0 "" "Go-http-client/1.1"


  1. Fork it
  2. Create your feature branch (git checkout -b my-new-feature)
  3. Commit your changes (git commit -am 'Add some feature')
  4. Test it (GEM_HOME=vendor bundle install; GEM_HOME=vendor bundle exec rake test)
  5. Push to the branch (git push origin my-new-feature)
  6. Create new Pull Request


Copyright (c) 2015 jimmidyson