# ⎈ Multi pod and container log tailing for Kubernetes -- Friendly fork of


*Fork of discontinued* [*wercker/stern*](https://github.com/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 or a Kubernetes resource in the form `<resource>/<name>` 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](https://github.com/stern/stern/releases)

### Build from source

```basic
go install github.com/stern/stern@latest
```

### asdf (Linux/macOS)

If you use [asdf](https://asdf-vm.com/), you can install like this:

```basic
asdf plugin-add stern
asdf install stern latest
```

### Homebrew (Linux/macOS)

If you use [Homebrew](https://brew.sh/), you can install like this:

```basic
brew install stern
```

### Krew (Linux/macOS/Windows)

If you use [Krew](https://krew.sigs.k8s.io/) which is the package manager for kubectl plugins, you can install like this:

```basic
kubectl krew install stern
```

## Usage

```basic
stern pod-query [flags]
```

The `pod-query` is a regular expression or a Kubernetes resource in the form `<resource>/<name>`.

The query is a regular expression when it is not a Kubernetes resource, so you could provide `"web-\w"` to tail `web-backend` and `web-frontend` pods but not `web-123`.

When the query is in the form `<resource>/<name>` (exact match), you can select all pods belonging to the specified Kubernetes resource, such as `deployment/nginx`. Supported Kubernetes resources are `pod`, `replicationcontroller`, `service`, `daemonset`, `deployment`, `replicaset`, `statefulset` and `job`.

### cli flags

| flag | default | purpose |
| --- | --- | --- |
| `--all-namespaces`, `-A` | `false` | 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` |  | Output stern command-line completion code for the specified shell. Can be 'bash', 'zsh' or 'fish'. |
| `--config` | `~/.config/stern/config.yaml` | Path to the stern config file |
| `--container`, `-c` | `.*` | Container name when multiple containers in pod. (regular expression) |
| `--container-colors` |  | Specifies the colors used to highlight container names. Use the same format as --pod-colors. Defaults to the values of --pod-colors if omitted, and must match its length. |
| `--container-state` | `all` | Tail containers with state in running, waiting, terminated, or all. 'all' matches all container states. To specify multiple states, repeat this or set comma-separated value. |
| `--context` |  | The name of the kubeconfig context to use |
| `--diff-container`, `-d` | `false` | Display different colors for different containers. |
| `--ephemeral-containers` | `true` | Include or exclude ephemeral containers. |
| `--exclude`, `-e` | `[]` | Log lines to exclude. (regular expression) |
| `--exclude-container`, `-E` | `[]` | Container name to exclude when multiple containers in pod. (regular expression) |
| `--exclude-pod` | `[]` | Pod name to exclude. (regular expression) |
| `--field-selector` |  | Selector (field query) to filter on. If present, default to ".\*" for the pod-query. |
| `--highlight`, `-H` | `[]` | Log lines to highlight. (regular expression) |
| `--include`, `-i` | `[]` | Log lines to include. (regular expression) |
| `--init-containers` | `true` | Include or exclude init containers. |
| `--kubeconfig` |  | Path to the kubeconfig file to use for CLI requests. |
| `--max-log-requests` | `-1` | Maximum number of concurrent logs to request. Defaults to 50, but 5 when specifying --no-follow |
| `--namespace`, `-n` |  | Kubernetes namespace to use. Default to namespace configured in kubernetes context. To specify multiple namespaces, repeat this or set comma-separated value. |
| `--no-follow` | `false` | Exit when all logs have been shown. |
| `--node` |  | Node name to filter on. |
| `--only-log-lines` | `false` | Print only log lines |
| `--output`, `-o` | `default` | Specify predefined template. Currently support: \[default, raw, json, extjson, ppextjson\] |
| `--pod-colors` |  | Specifies the colors used to highlight pod names. Provide colors as a comma-separated list using SGR (Select Graphic Rendition) sequences, e.g., "91,92,93,94,95,96". |
| `--prompt`, `-p` | `false` | Toggle interactive prompt for selecting 'app.kubernetes.io/instance' label values. |
| `--selector`, `-l` |  | Selector (label query) to filter on. If present, default to ".\*" for the pod-query. |
| `--show-hidden-options` | `false` | Print a list of hidden options. |
| `--since`, `-s` | `48h0m0s` | Return logs newer than a relative duration like 5s, 2m, or 3h. |
| `--stdin` | `false` | Parse logs from stdin. All Kubernetes related flags are ignored when it is set. |
| `--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. |
| `--template-file`, `-T` |  | Path to template to use for log lines, leave empty to use --output flag. It overrides --template option. |
| `--timestamps`, `-t` |  | Print timestamps with the specified format. One of 'default' or 'short' in the form '--timestamps=format' ('=' cannot be omitted). If specified but without value, 'default' is used. |
| `--timezone` | `Local` | Set timestamps to specific timezone. |
| `--verbosity` | `0` | Number of the log level verbosity |
| `--version`, `-v` | `false` | 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.

### config file

You can use the config file to change the default values of stern options. The default config file path is `~/.config/stern/config.yaml`.

```basic
# <flag name>: <value>
tail: 10
max-log-requests: 999
timestamps: short
```

You can change the config file path with `--config` flag or `STERNCONFIG` environment variable.

### 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](https://golang.org/pkg/text/template/#hdr-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) |
| `parseJSON` | `string` | Parse string as JSON |
| `tryParseJSON` | `string` | Attempt to parse string as JSON, return nil on failure |
| `extractJSONParts` | `string, ...string` | Parse string as JSON and concatenate the given keys. |
| `tryExtractJSONParts` | `string, ...string` | Attempt to parse string as JSON and concatenate the given keys. , return text on failure |
| `extjson` | `string` | Parse the object as json and output colorized json |
| `ppextjson` | `string` | Parse the object as json and output pretty-print colorized json |
| `toRFC3339Nano` | `object` | Parse timestamp (string, int, json.Number) and output it using RFC3339Nano format |
| `toTimestamp` | `object, string [, string]` | Parse timestamp (string, int, json.Number) and output it using the given layout in the timezone that is optionally given (defaults to UTC). |
| `levelColor` | `string` | Print log level using appropriate color |
| `colorBlack` | `string` | Print text using black color |
| `colorRed` | `string` | Print text using red color |
| `colorGreen` | `string` | Print text using green color |
| `colorYellow` | `string` | Print text using yellow color |
| `colorBlue` | `string` | Print text using blue color |
| `colorMagenta` | `string` | Print text using magenta color |
| `colorCyan` | `string` | Print text using cyan color |
| `colorWhite` | `string` | Print text using white color |

### Log level verbosity

You can configure the log level verbosity by the `--verbosity` flag. It is useful when you want to know how stern interacts with a Kubernetes API server in troubleshooting.

Increasing the verbosity increases the number of logs. `--verbosity 6` would be a good starting point.

### Max log requests

Stern has the maximum number of concurrent logs to request to prevent unintentional load to a cluster. The number can be configured by the `--max-log-requests` flag.

The behavior and the default are different depending on the presence of the `--no-follow` flag.

| `--no-follow` | default | behavior |
| --- | --- | --- |
| specified | 5 | limits the number of concurrent logs to request |
| not specified | 50 | exits with an error when if it reaches the concurrent limit |

The combination of `--max-log-requests 1` and `--no-follow` will be helpful if you want to show logs in order.

### Customize highlight colors

You can configure highlight colors for pods and containers in [the config file](https://github.com/stern/stern#config-file) using a comma-separated list of [SGR (Select Graphic Rendition) sequences](https://en.wikipedia.org/wiki/ANSI_escape_code#SGR_\(Select_Graphic_Rendition\)_parameters), as shown below. If you omit `container-colors`, the pod colors will be used as container colors as well.

```basic
# Green, Yellow, Blue, Magenta, Cyan, White
pod-colors: "32,33,34,35,36,37"

# Colors with underline (4)
# If empty, the pod colors will be used as container colors
container-colors: "32;4,33;4,34;4,35;4,36;4,37;4"
```

This format enables the use of various attributes, such as underline, background colors, 8-bit colors, and 24-bit colors, if your terminal supports them.

The equivalent flags `--pod-colors` and `--container-colors` are also available. The following command applies [24-bit colors](https://en.wikipedia.org/wiki/ANSI_escape_code#24-bit) using the `--pod-colors` flag.

```basic
# Monokai theme
podColors="38;2;255;97;136,38;2;169;220;118,38;2;255;216;102,38;2;120;220;232,38;2;171;157;242"
stern --pod-colors "$podColors" deploy/app
```

## Examples:

Tail all logs from all namespaces

```basic
stern . --all-namespaces
```

Tail the `kube-system` namespace without printing any prior logs

```basic
stern . -n kube-system --tail 0
```

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

```basic
stern envvars --context staging --container gateway
```

Tail the `staging` namespace excluding logs from `istio-proxy` container

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

Tail the `kube-system` namespace excluding logs from `kube-apiserver` pod

```basic
stern -n kube-system --exclude-pod kube-apiserver .
```

Show auth activity from 15min ago with timestamps

```basic
stern auth -t --since 15m
```

Show all logs of the last 5min by time, sorted by time

```basic
stern --since=5m --no-follow --only-log-lines -A -t . | sort -k4
```

Show auth activity with timestamps in specific timezone (default is your local timezone)

```basic
stern auth -t --timezone Asia/Tokyo
```

Follow the development of `some-new-feature` in minikube

```basic
stern some-new-feature --context minikube
```

View pods from another namespace

```basic
stern kubernetes-dashboard --namespace kube-system
```

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

```basic
stern --all-namespaces -l run=nginx
```

Follow the `frontend` pods in canary release

```basic
stern frontend --selector release=canary
```

Tail the pods on `kind-control-plane` node across all namespaces

```basic
stern --all-namespaces --field-selector spec.nodeName=kind-control-plane
```

Tail the pods created by `deployment/nginx`

```basic
stern deployment/nginx
```

Pipe the log message to jq:

```basic
stern backend -o json | jq .
```

Only output the log message itself:

```basic
stern backend -o raw
```

Output using a custom template:

```basic
stern --template '{{printf "%s (%s/%s/%s/%s)\n" .Message .NodeName .Namespace .PodName .ContainerName}}' backend
```

Output using a custom template with stern-provided colors:

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

Output using a custom template with `parseJSON`:

```basic
stern --template='{{.PodName}}/{{.ContainerName}} {{with $d := .Message | parseJSON}}[{{$d.level}}] {{$d.message}}{{end}}{{"\n"}}' backend
```

Output using a custom template that tries to parse JSON or fallbacks to raw format:

```basic
stern --template='{{.PodName}}/{{.ContainerName}} {{ with $msg := .Message | tryParseJSON }}[{{ colorGreen (toRFC3339Nano $msg.ts) }}] {{ levelColor $msg.level }} ({{ colorCyan $msg.caller }}) {{ $msg.msg }}{{ else }} {{ .Message }} {{ end }}{{"\n"}}' backend
```

Load custom template from file:

```basic
stern --template-file=~/.stern.tpl backend
```

Trigger the interactive prompt to select an 'app.kubernetes.io/instance' label value:

```basic
stern -p
```

Output log lines only:

```basic
stern . --only-log-lines
```

Read from stdin:

```basic
stern --stdin < service.log
```

## Completion

Stern supports command-line auto completion for bash, zsh or fish. `stern --completion=(bash|zsh|fish)` 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`, `--context`, `--node`, a resource query in the form `<resource>/<name>`, and flags with pre-defined choices.

If you use bash, stern bash completion code depends on the [bash-completion](https://github.com/scop/bash-completion). On the macOS, you can install it with homebrew as follows:

```basic
# 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`.

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

If installed via Krew, use:

```basic
source <(kubectl stern --completion bash)
complete -o default -F __start_stern kubectl stern
```

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

```basic
source <(stern --completion=zsh)
```

if you use fish shell, just source the stern fish completion code.

```basic
stern --completion=fish | source

# To load completions for each session, execute once:
stern --completion=fish >~/.config/fish/completions/stern.fish
```

## Running with container

You can also use stern using a container:

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

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

```basic
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](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.

```basic
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](https://github.com/stern/stern/blob/master/CONTRIBUTING.md) for details.