preq

Visit docs.prequel.dev for full documentation, examples, and guides.

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preq (pronounced "preek") is a free and open community-driven reliability problem detector

Use preq to:

• detect the latest bugs, misconfigurations, anti-patterns, and known issues from a community of practitioners
• provide engineers, on-call support, and SRE agents with impact and community-recommended mitigations
• hunt for new problems in distributed systems

preq is powered by Common Reliability Enumerations (CREs) that are contributed by the community and Prequel's Reliability Research Team. Reliability intelligence helps teams see a broad range of problems earlier, so they can prioritize, pinpoint, and reduce the risk of outages.

Install preq

Binary Distributions

Official binary distributions are available at latest release for Linux (amd64 and arm64), macOS (arm64), and Windows (amd64). All macOS binaries are signed and notarized. No configuration is necessary to start using preq.

Kubernetes

You can also install preq as a Krew plugin:

kubectl krew install preq

See https://docs.prequel.dev/install for more information.

Quick Usage

Step 1: Install and run the demo service (example macOS command below)

curl -sL "$(curl -s https://api.github.com/repos/prequel-dev/preq-demo-app/releases/latest \
  | jq -r '.assets[] | select(.name | test("demo-darwin-arm64$")) .browser_download_url')" \
  -o demo && chmod +x demo && ./demo > preq-demo.log 2>&1

Step 2: Trigger a problem

curl http://localhost:8080/panic

Step 3: Detect the problem

cat preq-demo.log | preq -o -

You will see a detection printed with the corresponding CRE ID, severity, and suggested mitigation.

Parsing rules           done! [3 rules in 3ms; 433 rules/s]
Problems detected       done! [1 in 7ms; 144/s]
Reading stdin           done! [208.64KB in 4ms; 53.01MB/s]
Matching lines          done! [1.01K lines in 4ms; 275.29K lines/s]
CRE-2025-0918        critical [1 hits @ 2025-03-11T10:00:19-04:00]

See our running preq guide for full walkthrough, including writing your own rules: https://docs.prequel.dev/running

Example CRE

This rule detects a specific sequence of events from one log source within a set time period. It also checks that a certain event does not occur during that period. If it does, the rule will not trigger.

cre:
  id: CRE-2024-0007
  severity: 0
  title: RabbitMQ Mnesia overloaded recovering persistent queues
  category: message-queue-problems
  author: Prequel
  description: |
    - The RabbitMQ cluster is processing a large number of persistent mirrored queues at boot. 
  cause: |
    - The Erlang process, Mnesia, is overloaded while recovering persistent queues on boot. 
  impact: |
    - RabbitMQ is unable to process any new messages and can cause outages in consumers and producers.
  tags: 
    - cre-2024-0007
    - known-problem
    - rabbitmq
  mitigation: |
    - Adjusting mirroring policies to limit the number of mirrored queues
    - Remove high-availability policies from queues
    - Add additional CPU resources and restart the RabbitMQ cluster
    - Use [lazy queues](https://www.rabbitmq.com/docs/lazy-queues) to avoid incurring the costs of writing data to disk 
  references:
    - https://groups.google.com/g/rabbitmq-users/c/ekV9tTBRZms/m/1EXw-ruuBQAJ
  applications:
    - name: "rabbitmq"
      version: "3.9.x"
metadata:
  kind: prequel
  id: 5UD1RZxGC5LJQnVpAkV11A
  generation: 1
rule:
  sequence:
    window: 30s
    event:
      src: log
      container_name: rabbitmq
    order:
      - regex: Discarding message(.+)in an old incarnation(.+)of this node
      - Mnesia is overloaded
    negate:
      - SIGTERM received - shutting down

Automated Actions using preq

You can connect detections to automated runbooks that take action when a CRE fires. For example, restarting a service or notifying your on-call team.

You can run automated actions on new detections using preq -a <actions.yaml>.

See https://docs.prequel.dev/running#automated-runbooks for examples of how to setup automated runbooks when a CRE is detected and trigger actions like:

• Slack Notifications
• Jira Issue Creation
• Runbook executables
• CronJobs

Data sources other than stdin

preq works on any timestamped data source, not just stdin. You can define multiple sources (e.g., app logs, system logs, metric dumps) in a YAML template and let preq automatically map CRE rules to the right data.

Learn more about data sources here: https://docs.prequel.dev/data-sources

Community

We are building an open reliability detection community and we would love you to join!

• Slack: Ask questions, share detections, propose new CREs.

• Playground: Try rules in your browser with WebAssembly, no data leaves your machine.

• Docs: Explore the documentation to learn how to install, run, automate, and write CREs.

• CRE Repository: Contribute new community detection rules and help the reliability community grow.

Contributing

We welcome contributions of all kinds: bug fixes, docs, new CRE rules, or feature ideas!

See the contribution guide for more details: https://docs.prequel.dev/cres/contributing

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Licensed under the Apache License 2.0