stern

Fork of discontinued wercker/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

Download binary

Download a binary release

Build from source

go get -u github.com/stern/stern

asdf (Linux/macOS)

If you use asdf, you can install like this:

asdf plugin-add stern
asdf install stern latest

Homebrew (Linux/macOS)

If you use Homebrew, you can install like this:

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
--all-namespaces, -A		If present, tail across all namespaces. A specific namespace is ignored even if specified with --namespace.
--color	auto	Force set color output. auto: colorize if tty attached, always: always colorize, never: never colorize
--completion		Outputs stern command-line completion code for the specified shell. Can be 'bash' or 'zsh'
--container, -c	.*	Container name when multiple containers in pod (regular expression)
--container-state	running	Tail containers with status in running, waiting or terminated. Default to running.
--context		Kubernetes context to use. Default to kubectl config current-context
--exclude, -e		Log lines to exclude; specify multiple with additional --exclude; (regular expression)
--exclude-container, -E		Container name to exclude when multiple containers in pod (regular expression)
--help, -h		Output Usage and Flags details
--include, -i		Log lines to include; specify multiple with additional --include; (regular expression)
--init-containers	true	Include or exclude init containers
--kubeconfig	see note	Path to kubeconfig file to use. Default to KUBECONFIG variable then ~/.kube/config path
--namespace, -n		Kubernetes namespace to use. Default to namespace configured in Kubernetes context
--output, -o	default	Specify predefined template. Currently support: [default, raw, json] See templates section
--selector, -l		Selector (label query) to filter on. If present, default to .* for the pod-query.
--since, -s	48h	Return logs newer than a relative duration like 5s, 2m, or 3h. Defaults to 48h.
--tail	-1	The number of lines from the end of the logs to show. Defaults to -1, showing all logs.
--template		Template to use for log lines, leave empty to use --output flag
--timestamps, -t		Print timestamps
--version, -v		Print the version and exit

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
NodeName	string	The node name where the pod is scheduled on
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 '{{printf "%s (%s/%s/%s/%s)\n" .Message .NodeName .Namespace .PodName .ContainerName}}' backend

Output using a custom template with stern-provided colors:

stern --template '{{.Message}} ({{.Namespace}}/{{color .PodColor .PodName}}/{{color .ContainerColor .ContainerName}}){{"\n"}}' 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:

# If running Bash 3.2
brew install bash-completion

# or, if running Bash 4.1+
brew install bash-completion@2

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

source "$(brew --prefix)/etc/profile.d/bash_completion.sh"
source <(stern --completion=bash)

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

source <(stern --completion=zsh)

Running with container

You can also use stern using a container:

docker run ghcr.io/stern/stern --version

If you are using a minikube cluster, you need to run a container as follows:

docker run --rm -v "$HOME/.minikube:$HOME/.minikube" -v "$HOME/.kube:/$HOME/.kube" -e KUBECONFIG="$HOME/.kube/config" ghcr.io/stern/stern .

You can find image tags in https://github.com/orgs/stern/packages/container/package/stern.

Running in Kubernetes Pods

If you want to use stern in Kubernetes Pods, you need to create the following ClusterRole and bind it to ServiceAccount.

apiVersion: rbac.authorization.k8s.io/v1
kind: ClusterRole
metadata:
  name: stern
rules:
- apiGroups: [""]
  resources: ["pods", "pods/log"]
  verbs: ["get", "watch", "list"]

Contributing to this repository

Please see CONTRIBUTING for details.