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jstern

Jstern is a command-line tool for filtering and formatting JSON logs from Kubernetes pods using the stern CLI. This tool allows you to extract specific keys, apply filters, and pretty-print JSON logs with enhanced readability using colored output.

Prerequisites

  • Stern CLI: stern must be installed as a prerequisite for jstern. Stern is used to fetch Kubernetes logs.

You can install stern by following the instructions on its official GitHub repository.

Installation

Download the latest release from the releases page and extract the binary to a directory in your system path.

Build from Source

  1. Make sure you have Rust and Cargo installed on your system.
  2. Clone this repository and build the project:
git clone https://github.com/uherman/jstern
cd jstern
cargo build --release
  1. Ensure jstern is executable and available in your system path.

For MacOS and Linux, you can copy the binary to a directory in your system path:

cp target/release/jstern /usr/local/bin

Usage

jstern <pod_query> [options]

Options

  • -n, --namespace <namespace> Specify the Kubernetes namespace. If not provided, the current namespace will be used.

  • -s, --selector <selector> Use a selector to extract specific values from the output JSON. The selector can point to nested fields (e.g., metadata.name).

  • -k, --keys <key1 key2 ...> Extract specific keys from the output JSON logs. Multiple keys can be provided. Supports dot notation for nested fields (e.g., metadata.name).

  • -f, --filter <key> <value> Apply a filter to the logs, only outputting logs where the given JSON key matches the specified value. Multiple filters can be applied.

  • --separator Print a separator between each log entry for improved readability.

  • --padding Add extra blank lines between each log entry to visually separate the logs.

  • -h, --help Display help message.

Examples

  1. Basic Usage: Fetch logs from a pod with a given name in the default namespace:
jstern my-pod
  1. Specify Namespace: Fetch logs from a pod in a specific namespace:
jstern my-pod -n my-namespace
  1. Select Specific Fields: Extract specific keys from the JSON logs:
jstern my-pod -k metadata.name status.phase
  1. Apply Filters: Filter logs where the status.phase is Running:
jstern my-pod -f status.phase Running
  1. Use a Selector: Use a selector to extract the value of a specific field:
jstern my-pod -s metadata.name
  1. Pretty Output with Separator and Padding: Print logs with a separator between each entry and padding around entries:
jstern my-pod --separator --padding

How It Works

  • jstern uses stern to fetch raw logs from Kubernetes.
  • The tool then parses the logs as JSON and allows you to apply selectors, extract keys, or filter entries based on specified conditions.
  • It formats the output using colored JSON for better readability and can optionally add separators or padding between log entries.

Contributing

Feel free to open issues or submit pull requests if you'd like to contribute to the project.

License

This project is licensed under the MIT License. See the LICENSE file for more details.