Riemann

Paid APILinuxSelf-hostedWeb

What Riemann is

Riemann monitors distributed systems by collecting events from servers and applications, then processing event streams to help teams interpret system behavior. Events can describe exceptions and request latency, as well as host CPU, memory, and disk state. Configurable streams written in Clojure can filter, combine, alter, and act on events; custom functions can extend the configuration. Its index keeps the latest event for each host and service until its TTL expires. A dashboard displays queried state and can show matching events in real time over websockets. Alerts include email, with PagerDuty integration for SMS or phone notifications. Riemann can forward streams to Graphite and includes a Librato Metrics integration. Clients submit events and query the index using Protocol Buffers over TCP or UDP, and libraries are listed for many programming languages. The maker describes performance of millions of events per second on commodity x86 hardware, while noting UDP can lose events. Riemann is open source and free. It does not automatically shard workloads, so operators must design sharding and aggregation.

Who it suits

Riemann suits operations staff managing large, dynamic infrastructure and engineers investigating production errors or performance bottlenecks. It is particularly relevant to teams comfortable configuring event flows in Clojure and designing their own sharding approach.

What it does well

Processes configurable event streams in Clojure
Dashboard can display matching events live
Supports email and PagerDuty alerts
Integrates with Graphite and Librato Metrics
Open source and free

What to know first

UDP can lose events
Workloads do not shard automatically
Configuration is written in Clojure

Limits

Riemann does not automatically shard workloads, so users must choose sharding axes and build aggregation and discovery mechanics. UDP is lossy; TCP is recommended when reliable delivery and acknowledgement matter.

Getting started

Visit https://riemann.io/.
Choose an installation route such as the tarball, Debian or RPM package, Puppet, Vagrant, Chef, or Docker.
Configure streams in Clojure and submit events using Protocol Buffers over TCP or UDP.
Use TCP when reliable event delivery and acknowledgement matter.
Connect clients using a library for a supported language.

Verdict

Riemann offers event collection, stream processing, dashboards, and alert integrations for distributed systems monitoring. Teams should account for its manual sharding requirement and use TCP when reliable event delivery and acknowledgement matter.

Questions

Is Riemann free?

Yes. It is free and open source.

Which platforms does it support?

The listed platforms are API, Linux, self-hosted, and web.

How do clients send events?

Clients use Protocol Buffers over TCP or UDP to submit events and query the index.

Can Riemann send alerts?

It supports email alerts and can integrate with PagerDuty for SMS or phone alerts.

Does it integrate with monitoring and metrics services?

Event streams can be forwarded to Graphite, and a Librato Metrics integration is described.

Where can users get support?

The support page directs users to IRC, the mailing list, or GitHub Issues.

Facts from Riemann's own pages

Alerts: Riemann can throttle or roll up events into email alerts and integrate with PagerDuty for SMS or phone alerts. · riemann.io, 11 Oct 2026
Audience: The maker describes Riemann as intended for operations staff managing large dynamic infrastructure and engineers investigating production errors and performance bottlenecks. · riemann.io, 11 Oct 2026
Client languages: The clients page lists libraries for C, C++, C#, Clojure, Elixir, Erlang, Go, Java, Lua, Node.js, OCaml, Perl, Python, Ruby, Rust, and Scala. · riemann.io, 11 Oct 2026
Client protocol: Clients use Protocol Buffers over TCP or UDP to submit events and query the index. · riemann.io, 11 Oct 2026
Configuration: Riemann configuration is a Clojure program that can be extended with custom functions. · riemann.io, 11 Oct 2026
Dashboard: Riemann-dash uses websockets to display interactive visualizations of the Riemann index. · riemann.io, 11 Oct 2026
Dashboards: The dashboard displays queried system state and can show matching events in real time over websockets. · riemann.io, 4 Oct 2026
Deployment: The maker documents running Riemann in Docker and provides a prepackaged riemannio/riemann image. · riemann.io, 11 Oct 2026
Event data: Events can include host, service, state, time, description, tags, metric, TTL, and custom fields. · riemann.io, 11 Oct 2026
Event processing: Riemann filters, combines, and acts on event flows to help understand systems. · riemann.io, 11 Oct 2026
Integrations: The maker lists forwarding events to Graphite and a built-in Librato Metrics integration. · riemann.io, 11 Oct 2026
Intended users: The site describes Riemann as intended for operations staff managing large, dynamic infrastructure and engineers investigating production errors and performance bottlenecks. · riemann.io, 4 Oct 2026
Limits: Riemann cannot automatically shard workloads, so users must choose sharding axes and build the aggregation and discovery mechanics. · riemann.io, 11 Oct 2026
Monitoring: Events can report application exceptions and request latency as well as host CPU, memory, and disk state. · riemann.io, 4 Oct 2026
Operational limit: The site notes that UDP is lossy and recommends TCP for reliable delivery and acknowledgement. · riemann.io, 4 Oct 2026
Performance: The site says a stock configuration on commodity x86 hardware can handle millions of events per second at sub-millisecond latency, with 99th-percentile latency around 5 ms. · riemann.io, 4 Oct 2026
Protocols: Riemann accepts Protocol Buffers over TCP and UDP; its documented servers also include TLS and websockets. · riemann.io, 4 Oct 2026
Purpose: Riemann aggregates events from servers and applications and processes them with a stream processing language. · riemann.io, 11 Oct 2026
Security: Riemann supports bidirectional TLS authentication for TCP connections, and its documentation also describes using a VPN or SSH tunnel. · riemann.io, 11 Oct 2026
Speed: The maker says a stock configuration on commodity x86 hardware can handle millions of events per second at sub-millisecond latencies, with 99th percentile latency around 5 ms. · riemann.io, 11 Oct 2026
State index: Its index stores the latest event for each host and service, and removes entries when their TTL expires. · riemann.io, 11 Oct 2026
Stream processing: Its configurable streams can filter, combine, alter, and act on events, and the configuration is written in Clojure. · riemann.io, 4 Oct 2026
Support: The maker directs users to IRC, a mailing list, or GitHub Issues for help and describes Riemann as a volunteer effort. · riemann.io, 11 Oct 2026

Where Riemann stands on Freedom251

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