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
Govendor is required to install vendored dependencies.
mkdir -p $GOPATH/src/github.com/wercker
cd $GOPATH/src/github.com/wercker
git clone https://github.com/wercker/stern.git && cd stern
govendor sync
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.
