Updates to Component Overview (#7208)
* Updates to Component Overview * Changed VMs to machines -- it can be both VM or physical machine. * Separated Addons from Master section, since it depends on an addon if it's components are executed on Master or Node. * Fix ID of Kubelet glossary * Removed fluentd and supervisord These are not necessary to mention here in the overview. * fluentd is one of Cluster-level Logging solutions briefly described in Addons Section * supervisord is not required to be run on the Node * Requested change - remove Addons manager reference * After review updates * Updated the Addons page reference
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Jakub Nowakowski
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@@ -15,9 +15,9 @@ deliver a functioning Kubernetes cluster.
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Master components provide the cluster's control plane. Master components make global decisions about the
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cluster (for example, scheduling), and detecting and responding to cluster events (starting up a new pod when a replication controller's 'replicas' field is unsatisfied).
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Master components can be run on any node in the cluster. However,
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Master components can be run on any machine in the cluster. However,
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for simplicity, set up scripts typically start all master components on
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the same VM, and do not run user containers on this VM. See
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the same machine, and do not run user containers on this machine. See
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[Building High-Availability Clusters](/docs/admin/high-availability/) for an example multi-master-VM setup.
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### kube-apiserver
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@@ -46,7 +46,7 @@ These controllers include:
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### cloud-controller-manager
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cloud-controller-manager runs controllers that interact with the underlying cloud providers. The cloud-controller-manager binary is an alpha feature introduced in Kubernetes release 1.6.
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[cloud-controller-manager](/docs/tasks/administer-cluster/running-cloud-controller/) runs controllers that interact with the underlying cloud providers. The cloud-controller-manager binary is an alpha feature introduced in Kubernetes release 1.6.
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cloud-controller-manager runs cloud-provider-specific controller loops only. You must disable these controller loops in the kube-controller-manager. You can disable the controller loops by setting the `--cloud-provider` flag to `external` when starting the kube-controller-manager.
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@@ -59,15 +59,32 @@ The following controllers have cloud provider dependencies:
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* Service Controller: For creating, updating and deleting cloud provider load balancers
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* Volume Controller: For creating, attaching, and mounting volumes, and interacting with the cloud provider to orchestrate volumes
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### addons
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## Node Components
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Node components run on every node, maintaining running pods and providing the Kubernetes runtime environment.
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### kubelet
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{% glossary_definition term_id="kubelet" length="all" %}
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### kube-proxy
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[kube-proxy](/docs/admin/kube-proxy/) enables the Kubernetes service abstraction by maintaining
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network rules on the host and performing connection forwarding.
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### Container Runtime
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The container runtime is the software that is responsible for running containers. Kubernetes supports two runtimes: [Docker](http://www.docker.com) and [rkt](https://coreos.com/rkt/).
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## Addons
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Addons are pods and services that implement cluster features. The pods may be managed
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by Deployments, ReplicationControllers, and so on. Namespaced addon objects are created in
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the `kube-system` namespace.
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Addon manager creates and maintains addon resources. See [here](http://releases.k8s.io/HEAD/cluster/addons) for more details.
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Selected addons are described below, for an extended list of available addons please see [Addons](/docs/concepts/cluster-administration/addons/).
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#### DNS
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### DNS
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While the other addons are not strictly required, all Kubernetes clusters should have [cluster DNS](/docs/concepts/services-networking/dns-pod-service/), as many examples rely on it.
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@@ -75,58 +92,20 @@ Cluster DNS is a DNS server, in addition to the other DNS server(s) in your envi
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Containers started by Kubernetes automatically include this DNS server in their DNS searches.
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#### Web UI (Dashboard)
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### Web UI (Dashboard)
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[Dashboard](/docs/tasks/access-application-cluster/web-ui-dashboard/) is a general purpose, web-based UI for Kubernetes clusters. It allows users to manage and troubleshoot applications running in the cluster, as well as the cluster itself.
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#### Container Resource Monitoring
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### Container Resource Monitoring
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[Container Resource Monitoring](/docs/tasks/debug-application-cluster/resource-usage-monitoring/) records generic time-series metrics
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about containers in a central database, and provides a UI for browsing that data.
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#### Cluster-level Logging
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### Cluster-level Logging
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A [Cluster-level logging](/docs/concepts/cluster-administration/logging/) mechanism is responsible for
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saving container logs to a central log store with search/browsing interface.
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## Node components
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Node components run on every node, maintaining running pods and providing the Kubernetes runtime environment.
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### kubelet
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[kubelet](/docs/admin/kubelet/) is the primary node agent. It watches for pods that have been assigned to its node (either by apiserver or via local configuration file) and:
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* Mounts the pod's required volumes.
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* Downloads the pod's secrets.
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* Runs the pod's containers via docker (or, experimentally, rkt).
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* Periodically executes any requested container liveness probes.
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* Reports the status of the pod back to the rest of the system, by creating a *mirror pod* if necessary.
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* Reports the status of the node back to the rest of the system.
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### kube-proxy
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[kube-proxy](/docs/admin/kube-proxy/) enables the Kubernetes service abstraction by maintaining
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network rules on the host and performing connection forwarding.
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### docker
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`docker` is used for running containers.
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### rkt
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`rkt` is supported experimentally for running containers as an alternative to docker.
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### supervisord
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`supervisord` is a lightweight process monitor and control system that can be used to keep kubelet and docker
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running.
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### fluentd
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`fluentd` is a daemon which helps provide [cluster-level logging](#cluster-level-logging).
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{% endcapture %}
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{% include templates/concept.md %}
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