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Cortex

Cortex (cortexmetrics.io) is the CNCF open-source horizontally-scalable Prometheus-compatible metrics backend. Originally started by Grafana Labs engineers, it became the architectural foundation for three Grafana-Labs-authored observability databases:

  • Mimir (metrics) — Grafana Labs' forked successor.
  • Loki (logs) — started from the same foundation.
  • Pyroscope 1.x (continuous profiles) — built on Cortex.

Why it's on this wiki

Cortex is the common architectural ancestor the Grafana Labs retrospective in the Pyroscope 2.0 launch post explicitly names: "the same foundation that the Mimir and Loki projects started with."

All three of those projects have since outgrown it — and the rearchitecture story is substantially the same across them. The Cortex → object-store rearchitecture pattern is the shared direction.

Core Cortex traits (the ones being retired)

  • Write-path replication. Each sample replicated N-way across ingesters for durability on the hot path. Doubles/triples ingest-tier compute and network.
  • Coupled read and write paths. Ingesters serve both recent reads and buffer writes, making independent scaling awkward.
  • Object storage as secondary, not primary. Data flushed to S3/GCS after local-ingester retention, with the ingester tier authoritative for recent data.

These were sensible early-2010s defaults for a Prometheus remote-write backend. At observability-DB scale across metrics, logs, and profiles, they became the dominant cost. (Source: sources/2026-04-22-grafana-introducing-pyroscope-2-0)

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