NAME

kubelet - Processes a container manifest so the containers are launched according to how they are described.

SYNOPSIS

kubelet [OPTIONS]

DESCRIPTION

The kubernetes kubelet runs on each node. The Kubelet works in terms of a container manifest. A container manifest is a YAML or JSON file that describes a pod. The Kubelet takes a set of manifests that are provided in various mechanisms and ensures that the containers described in those manifests are started and continue running.

There are 4 ways that a container manifest can be provided to the Kubelet:

File Path passed as a flag on the command line. This file is rechecked every 20 seconds (configurable with a flag).
HTTP endpoint HTTP endpoint passed as a parameter on the command line. This endpoint is checked every 20 seconds (also configurable with a flag).
etcd server The Kubelet will reach out and do a watch on an etcd server. The etcd path that is watched is /registry/hosts/$(hostname -f). As this is a watch, changes are noticed and acted upon very quickly.
HTTP server The kubelet can also listen for HTTP and respond to a simple API (underspec'd currently) to submit a new manifest.

OPTIONS

-address="127.0.0.1" The address for the info server to serve on (set to 0.0.0.0 or "" for all interfaces).

-allow_privileged=false If true, allow containers to request privileged mode. [default=false].

-alsologtostderr=false log to standard error as well as files.

-config="" Path to the config file or directory of files.

-docker_endpoint="" If non-empty, use this for the docker endpoint to communicate with.

-enable_server=true Enable the info server.

-etcd_servers=[] List of etcd servers to watch (http://ip:port), comma separated.

-file_check_frequency=20s Duration between checking config files for new data.

-hostname_override="" If non-empty, will use this string as identification instead of the actual hostname.

-http_check_frequency=20s Duration between checking http for new data.

-log_backtrace_at=:0 when logging hits line file:N, emit a stack trace.

-log_dir="" If non-empty, write log files in this directory.

-log_flush_frequency=5s Maximum number of seconds between log flushes.

-logtostderr=false log to standard error instead of files.

-manifest_url="" URL for accessing the container manifest.

-network_container_image="kubernetes/pause:latest" The image that network containers in each pod will use.

-port=10250 The port for the info server to serve on.

-registry_burst=10 Maximum size of a bursty pulls, temporarily allows pulls to burst to this number, while still not exceeding registry_qps. Only used if --registry_qps > 0.

-registry_qps=0 If > 0, limit registry pull QPS to this value. If 0, unlimited. [default=0.0].

-root_dir="/var/lib/kubelet" Directory path for managing kubelet files (volume mounts,etc).

-stderrthreshold=0 logs at or above this threshold go to stderr.

-sync_frequency=10s Max period between synchronizing running containers and config.

-v=0 log level for V logs.

-version=false Print version information and quit.

-vmodule= comma-separated list of pattern=N settings for file-filtered logging.

EXAMPLES

The kubelet can be called manually or from systemd. An example unit file looks as such:

[Unit]
Description=Kubernetes Kubelet
After=docker.socket cadvisor.service
Requires=docker.socket

[Service]
EnvironmentFile=/etc/kubernetes/config
EnvironmentFile=/etc/kubernetes/kubelet
ExecStart=/usr/bin/kubelet \
	--logtostderr=${KUBE_LOGTOSTDERR} \
	--v=${KUBE_LOG_LEVEL} \
	--etcd_servers=${KUBE_ETCD_SERVERS} \
	--address=${MINION_ADDRESS} \
	--port=${MINION_PORT} \
    --hostname_override=${MINION_HOSTNAME} \
    --allow_privileged=${KUBE_ALLOW_PRIV}
Restart=on-failure

[Install]
WantedBy=multi-user.target

Where the variables are stored in the /etc/kubernetes/ environment files.

HISTORY

October 2014, Originally compiled by Scott Collier (scollier at redhat dot com) based on the kubernetes source material and internal work.

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