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83 lines
4.1 KiB
Markdown
83 lines
4.1 KiB
Markdown
# Elasticsearch Add-On
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This add-on consists of a combination of [Elasticsearch][elasticsearch],
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[Fluentd][fluentd] and [Kibana][kibana]. Elasticsearch is a search engine
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that is responsible for storing our logs and allowing for them to be queried.
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Fluentd sends log messages from Kubernetes to Elasticsearch, whereas Kibana
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is a graphical interface for viewing and querying the logs stored in
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Elasticsearch.
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**Note:** this addon should **not** be used as-is in production. This is
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an example and you should treat it as such. Please see at least the
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[Security](#security) and the [Storage](#storage) sections for more
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information.
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## Elasticsearch
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Elasticsearch is deployed as a [StatefulSet][statefulSet], which is like
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a Deployment, but allows for maintaining state on storage volumes.
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### Security
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Elasticsearch has capabilities to enable authorization using the
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[X-Pack plugin][xPack]. See configuration parameter `xpack.security.enabled`
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in Elasticsearch and Kibana configurations. It can also be set via the
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`XPACK_SECURITY_ENABLED` env variable. After enabling the feature,
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follow [official documentation][setupCreds] to set up credentials in
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Elasticsearch and Kibana. Don't forget to propagate those credentials also to
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Fluentd in its [configuration][fluentdCreds], using for example
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[environment variables][fluentdEnvVar]. You can utilize [ConfigMaps][configMap]
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and [Secrets][secret] to store credentials in the Kubernetes apiserver.
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### Initialization
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The Elasticsearch StatefulSet manifest specifies that there shall be an
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[init container][initContainer] executing before Elasticsearch containers
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themselves, in order to ensure that the kernel state variable
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`vm.max_map_count` is at least 262144, since this is a requirement of
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Elasticsearch. You may remove the init container if you know that your host
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OS meets this requirement.
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### Storage
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The Elasticsearch StatefulSet will use the [EmptyDir][emptyDir] volume to
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store data. EmptyDir is erased when the pod terminates, here it is used only
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for testing purposes. **Important:** please change the storage to persistent
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volume claim before actually using this StatefulSet in your setup!
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## Fluentd
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Fluentd is deployed as a [DaemonSet][daemonSet] which spawns a pod on each
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node that reads logs, generated by kubelet, container runtime and containers
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and sends them to Elasticsearch.
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**Note:** in order for Fluentd to work, every Kubernetes node must be labeled
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with `beta.kubernetes.io/fluentd-ds-ready=true`, as otherwise the Fluentd
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DaemonSet will ignore them.
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Learn more in the [official Kubernetes documentation][k8sElasticsearchDocs].
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### Known problems
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Since Fluentd talks to the Elasticsearch service inside the cluster, instances
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on masters won't work, because masters have no kube-proxy. Don't mark masters
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with the label mentioned in the previous paragraph or add a taint on them to
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avoid Fluentd pods scheduling there.
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[fluentd]: http://www.fluentd.org/
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[elasticsearch]: https://www.elastic.co/products/elasticsearch
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[kibana]: https://www.elastic.co/products/kibana
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[xPack]: https://www.elastic.co/products/x-pack
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[setupCreds]: https://www.elastic.co/guide/en/x-pack/current/setting-up-authentication.html#reset-built-in-user-passwords
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[fluentdCreds]: https://github.com/uken/fluent-plugin-elasticsearch#user-password-path-scheme-ssl_verify
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[fluentdEnvVar]: https://docs.fluentd.org/v0.12/articles/faq#how-can-i-use-environment-variables-to-configure-parameters-dynamically
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[configMap]: https://kubernetes.io/docs/tasks/configure-pod-container/configure-pod-configmap/
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[secret]: https://kubernetes.io/docs/concepts/configuration/secret/
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[statefulSet]: https://kubernetes.io/docs/concepts/workloads/controllers/statefulset
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[initContainer]: https://kubernetes.io/docs/concepts/workloads/pods/init-containers/
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[emptyDir]: https://kubernetes.io/docs/concepts/storage/volumes#emptydir
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[daemonSet]: https://kubernetes.io/docs/concepts/workloads/controllers/daemonset/
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[k8sElasticsearchDocs]: https://kubernetes.io/docs/tasks/debug-application-cluster/logging-elasticsearch-kibana
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[]()
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