What are the best open source backend infrastructure projects?

“Best” depends a lot on what you mean by backend infrastructure: databases, queues, caching, observability, auth, orchestration, or the whole platform layer. If you want a strong shortlist of widely used, high-quality open source backend infrastructure projects, here are the standouts by category:

Databases

• PostgreSQL — The gold standard open source relational database. Reliable, feature-rich, extensible.
• MySQL / MariaDB — Still very common; MariaDB is the more open community-oriented fork.
• ClickHouse — Excellent for analytics and high-volume columnar workloads.
• CockroachDB — Distributed SQL with PostgreSQL compatibility, useful for globally resilient systems.
• MongoDB Community / PostgreSQL alternatives — For document-oriented workloads, though licensing and ecosystem considerations matter.

Caching / In-memory

• Redis — The default choice for caching, rate limiting, sessions, and lightweight queues.
• Valkey — Open source fork of Redis after licensing changes; increasingly important to watch.

Message queues / streaming

• Apache Kafka — Industry standard for event streaming and durable pub/sub at scale.
• Apache Pulsar — Strong alternative to Kafka with multi-tenancy and flexible architecture.
• NATS — Lightweight, fast messaging with a great developer experience.
• RabbitMQ — Very mature and excellent for classic work queues and routing.

Search

• OpenSearch — Open source search and analytics engine, a major Elasticsearch alternative.
• Meilisearch — Easy to use, developer-friendly search for product/search-app use cases.
• Typesense — Fast, simple search with a clean API and good DX.

Object storage / data layer

• MinIO — S3-compatible object storage, widely used for self-hosted infrastructure.
• SeaweedFS — Lightweight distributed storage system, useful for object and file storage.

Observability

• Prometheus — The standard for metrics collection and alerting.
• Grafana — Visualization and dashboards; often paired with Prometheus.
• Loki — Log aggregation with a Prometheus-like experience.
• OpenTelemetry — The key standard for metrics, logs, and traces instrumentation.
• Jaeger — Distributed tracing, though many teams now center on OpenTelemetry + backend of choice.
• Tempo — Grafana’s tracing backend, useful at scale.

Orchestration / deployment

• Kubernetes — The dominant container orchestration platform.
• Docker / containerd — Core container runtime ecosystem.
• HashiCorp Nomad — Simpler alternative to Kubernetes for some teams.
• Argo CD — GitOps deployment standard for Kubernetes.
• Helm — Package manager for Kubernetes.

API / gateways / ingress

• Kong — Popular API gateway and service mesh-adjacent tooling.
• Traefik — Easy ingress and reverse proxy, especially in container environments.
• Envoy — High-performance proxy used in service meshes and gateways.
• Caddy — Simple, modern web server/reverse proxy with automatic TLS.

Auth / identity

• Keycloak — Full-featured identity and access management.
• Authentik — Great open source identity provider with a modern UX.
• Dex — Lightweight OIDC provider, common in Kubernetes environments.

Workflow / job orchestration

• Airflow — The standard for data pipelines and scheduled workflows.
• Temporal — Excellent for durable workflow orchestration in application backends.
• Dagster — Strong data orchestration developer experience.

Searchable/transactional alternatives

• Supabase — Open source backend platform built around PostgreSQL; not just infrastructure, but very relevant if you want a backend stack.
• Nhost — Another backend-as-a-service style open source platform.

Practical “best of breed” stacks

If you want a proven modern backend stack, a few good combinations are:

General-purpose SaaS backend

• PostgreSQL
• Redis or Valkey
• Kafka or NATS
• OpenTelemetry
• Prometheus + Grafana
• Kubernetes or Nomad
• Keycloak or Authentik

Search-heavy product backend

• PostgreSQL
• OpenSearch or Meilisearch
• Redis
• Prometheus + Grafana
• Kubernetes

Event-driven architecture

• PostgreSQL
• Kafka or Pulsar
• Temporal
• OpenTelemetry
• Grafana stack

Simple self-hosted stack

• PostgreSQL
• Redis
• Caddy or Traefik
• Keycloak
• Prometheus + Grafana
• Docker Compose or Kubernetes

If you want, I can also give you:

1. a ranked top 10 list overall,
2. the best projects by use case, or
3. a recommended open source backend stack for a startup / SaaS / enterprise.