Use JSON logs and Loki to store them

Cost

Open source. Pino and Loki are free to run on your own servers. Managed log storage from several vendors is paid.

How to do it

JSON lines work with any store, so the format is the lasting choice and the store can change. Pino on npm reached 1.0 in March 2016 and has about 33 million weekly downloads. Structlog on PyPI is under MIT or Apache-2.0 and has about 25 million. Loki reached 1.0 in November 2019, is under AGPLv3, and 3.7.9 came out on 20 October 2026. Its image has over 4.8 billion pulls on Docker Hub. Loki indexes labels only, so it costs little to run next to Grafana. The fields to log are in Write structured logs. Choose something else when you need full-text search over every field, and use OpenSearch.

Examples

Using these examples: they show one way to follow this rule. Keep the behaviour and the check, not the syntax. Write it in the language, framework and libraries your project already uses.

JavaScript example

import pino from 'pino';

const log = pino({ base: { service: 'orders-api' } });
log.info({ orderId: 'ord_123', durationMs: 84 }, 'order placed');

Python example

import structlog

structlog.configure(processors=[structlog.processors.add_log_level,
                                structlog.processors.TimeStamper(fmt="iso"),
                                structlog.processors.JSONRenderer()])
structlog.get_logger().info("order placed", order_id="ord_123", duration_ms=84)

How to check

A script reads 100 lines of production log output, and every line parses as JSON with a time, level and message. A query in the store finds a test line within 60 seconds.

Sources

• Grafana Loki documentation
• Grafana licensing

Related rules

• Log structured events in Operations