stern

Stern allows you to tail multiple pods on Kubernetes and multiple containers within the pod. Each result is color coded for quicker debugging.

The query is a regular expression so the pod name can easily be filtered and you don't need to specify the exact id (for instance omitting the deployment id). If a pod is deleted it gets removed from tail and if a new pod is added it automatically gets tailed.

When a pod contains multiple containers Stern can tail all of them too without having to do this manually for each one. Simply specify the container flag to limit what containers to show. By default all containers are listened to.

Installation

If you don't want to build from source go grab a binary release

git clone https://github.com/wercker/stern.git && cd stern
go install

Homebrew

On macOS, you can also install Stern using Homebrew:

brew install stern

Usage

stern pod-query [flags]

The pod query is a regular expression so you could provide "web-\w" to tail web-backend and web-frontend pods but not web-123.

cli flags

flag	default	purpose
--container	.*	Container name when multiple containers in pod (regular expression)
--exclude-container		Container name to exclude when multiple containers in pod (regular expression)
--container-state	running	Tail containers with status in running, waiting or terminated. Default to running.
--timestamps		Print timestamps
--since		Return logs newer than a relative duration like 52, 2m, or 3h. Displays all if omitted
--context		Kubernetes context to use. Default to kubectl config current-context
--exclude		Log lines to exclude; specify multiple with additional --exclude; (regular expression)
--namespace		Kubernetes namespace to use. Default to namespace configured in Kubernetes context
--kubeconfig	~/.kube/config	Path to kubeconfig file to use
--all-namespaces		If present, tail across all namespaces. A specific namespace is ignored even if specified with --namespace.
--selector		Selector (label query) to filter on. If present, default to .* for the pod-query.
--tail	-1	The number of lines from the end of the logs to show. Defaults to -1, showing all logs.
--color	auto	Force set color output. auto: colorize if tty attached, always: always colorize, never: never colorize
--output	default	Specify predefined template. Currently support: [default, raw, json] See templates section
template		Template to use for log lines, leave empty to use --output flag

See stern --help for details

Stern will use the $KUBECONFIG environment variable if set. If both the environment variable and --kubeconfig flag are passed the cli flag will be used.

templates

stern supports outputting custom log messages. There are a few predefined templates which you can use by specifying the --output flag:

output	description
default	Displays the namespace, pod and container, and decorates it with color depending on --color
raw	Only outputs the log message itself, useful when your logs are json and you want to pipe them to jq
json	Marshals the log struct to json. Useful for programmatic purposes

It accepts a custom template through the --template flag, which will be compiled to a Go template and then used for every log message. This Go template will receive the following struct:

property	type	description
Message	string	The log message itself
Namespace	string	The namespace of the pod
PodName	string	The name of the pod
ContainerName	string	The name of the container

The following functions are available within the template (besides the builtin functions):

func	arguments	description
json	object	Marshal the object and output it as a json text
color	color.Color, string	Wrap the text in color (.ContainerColor and .PodColor provided)

Examples:

Tail the gateway container running inside of the envvars pod on staging

stern envvars --context staging --container gateway

Tail the staging namespace excluding logs from istio-proxy container

stern -n staging --exclude-container istio-proxy .

Show auth activity from 15min ago with timestamps

stern auth -t --since 15m

Follow the development of some-new-feature in minikube

stern some-new-feature --context minikube

View pods from another namespace

stern kubernetes-dashboard --namespace kube-system

Tail the pods filtered by run=nginx label selector across all namespaces

stern --all-namespaces -l run=nginx

Follow the frontend pods in canary release

stern frontend --selector release=canary

Pipe the log message to jq:

stern backend -o json | jq .

Only output the log message itself:

stern backend -o raw

Output using a custom template:

stern --template '{{.Message}} ({{.Namespace}}/{{.PodName}}/{{.ContainerName}})' backend

Output using a custom template with stern-provided colors:

stern --template '{{.Message}} ({{.Namespace}}/{{color .PodColor .PodName}}/{{color .ContainerColor .ContainerName}})' backend

Completion

Stern supports command-line auto completion for bash or zsh. stern --completion=(bash|zsh) outputs the shell completion code which work by being evaluated in .bashrc, etc for the specified shell. In addition, Stern supports dynamic completion for --namespace and --context. In order to use that, kubectl must be installed on your environment.

If you use bash, stern bash completion code depends on the bash-completion. On the macOS, you can install it with homebrew as follows:

$ brew install bash-completion

Note that bash-completion must be sourced before sourcing the stern bash completion code in .bashrc.

source <(brew --prefix)/etc/bash-completion
source <(stern --completion=bash)

If you use zsh, just source the stern zsh completion code in .zshrc.

source <(stern --completion=zsh)

Contributing to this repository

Oracle welcomes contributions to this repository from anyone. Please see CONTRIBUTING for details.