Prometheus + Thanos

Prometheus + Thanos

Prometheus is the de facto open-source system for collecting and querying time-series metrics, but a single Prometheus is limited by local storage and one cluster's view. Thanos extends Prometheus into a horizontally scalable, highly available, long-retention metrics platform with a global query view across many Prometheus instances.

This stack targets organizations running many clusters or needing months or years of metric history, typically in Kubernetes environments. It is a common choice for platform and SRE teams operating at scale.

Components

• Prometheus scrapes and stores metrics locally and evaluates alerting and recording rules.
• Thanos Sidecar runs alongside each Prometheus, uploading blocks to object storage and exposing data for global queries.
• Thanos Store Gateway serves historical data from object storage; Thanos Query fans out across sidecars and stores to give a single, deduplicated global view.
• Thanos Compactor downsamples and compacts long-term data for efficient retention.
• Object storage such as Amazon S3 holds long-term blocks cheaply.
• Grafana visualizes metrics; Kubernetes is the typical deployment substrate.

Strengths

Thanos gives Prometheus what it lacks: durable, cheap long-term storage in object stores, a global query across clusters, and high availability through deduplication of redundant Prometheus pairs. Downsampling keeps long-range queries fast. It reuses Prometheus and PromQL, so existing dashboards and alerts carry over. The components are modular, so you adopt only what you need.

Trade-offs

The stack adds operational complexity: several stateful components to deploy, secure, and tune. Object-storage latency affects historical queries unless caching is configured. Correct deduplication and retention require careful configuration. Running it well needs SRE expertise. For small single-cluster setups, plain Prometheus or a managed service is simpler and cheaper.

When to Use It

Use Prometheus + Thanos when you run multiple clusters or regions, need a unified global metrics view, require long-term retention beyond what local Prometheus storage allows, and want high availability — all while staying on open-source Prometheus and PromQL. For a single small cluster or when you prefer a managed offering, simpler alternatives like vanilla Prometheus or Grafana Mimir-based services may suit better.