open-consul/website/content/docs/architecture/jepsen.mdx

---
layout: docs
page_title: Jepsen Testing
description: >-
  Jepsen is a tool, written by Kyle Kingsbury, designed to test the partition
  tolerance of distributed systems. It creates network partitions while fuzzing
  the system with random operations. The results are analyzed to see if the
  system violates any of the consistency properties it claims to have.
---

# Jepsen Testing

[Jepsen](http://aphyr.com/posts/281-call-me-maybe-carly-rae-jepsen-and-the-perils-of-network-partitions)
is a tool, written by Kyle Kingsbury, designed to test the partition
tolerance of distributed systems. It creates network partitions while fuzzing
the system with random operations. The results are analyzed to see if the system
violates any of the consistency properties it claims to have.

As part of our Consul testing, we ran a Jepsen test to determine if
any consistency issues could be uncovered. In our testing, Consul
gracefully recovered from partitions without introducing any consistency
issues.

## Running the tests

At the moment, testing with Jepsen is rather complex as it requires
setting up multiple virtual machines, SSH keys, DNS configuration,
and a working Clojure environment. We hope to contribute our Consul
testing code upstream and to provide a Vagrant environment for Jepsen
testing soon.

## Output

Below is the output captured from Jepsen. We ran Jepsen multiple times,
and it passed each time. This output is only representative of a single
run and has been edited for length. Please reach out on [Consul's Discuss](https://discuss.hashicorp.com/c/consul)
if you would like to reproduce the Jepsen results.

<!--googleoff: all-->

```shell-session
$ lein test :only jepsen.system.consul-test

lein test jepsen.system.consul-test
INFO  jepsen.os.debian - :n5 setting up debian
INFO  jepsen.os.debian - :n3 setting up debian
INFO  jepsen.os.debian - :n4 setting up debian
INFO  jepsen.os.debian - :n1 setting up debian
INFO  jepsen.os.debian - :n2 setting up debian
INFO  jepsen.os.debian - :n4 debian set up
INFO  jepsen.os.debian - :n5 debian set up
INFO  jepsen.os.debian - :n3 debian set up
INFO  jepsen.os.debian - :n1 debian set up
INFO  jepsen.os.debian - :n2 debian set up
INFO  jepsen.system.consul - :n1 consul nuked
INFO  jepsen.system.consul - :n4 consul nuked
INFO  jepsen.system.consul - :n5 consul nuked
INFO  jepsen.system.consul - :n3 consul nuked
INFO  jepsen.system.consul - :n2 consul nuked
INFO  jepsen.system.consul - Running nodes: {:n1 false, :n2 false, :n3 false, :n4 false, :n5 false}
INFO  jepsen.system.consul - :n2 consul nuked
INFO  jepsen.system.consul - :n3 consul nuked
INFO  jepsen.system.consul - :n4 consul nuked
INFO  jepsen.system.consul - :n5 consul nuked
INFO  jepsen.system.consul - :n1 consul nuked
INFO  jepsen.system.consul - :n1 starting consul
INFO  jepsen.system.consul - :n2 starting consul
INFO  jepsen.system.consul - :n4 starting consul
INFO  jepsen.system.consul - :n5 starting consul
INFO  jepsen.system.consul - :n3 starting consul
INFO  jepsen.system.consul - :n3 consul ready
INFO  jepsen.system.consul - :n2 consul ready
INFO  jepsen.system.consul - Running nodes: {:n1 true, :n2 true, :n3 true, :n4 true, :n5 true}
INFO  jepsen.system.consul - :n5 consul ready
INFO  jepsen.system.consul - :n1 consul ready
INFO  jepsen.system.consul - :n4 consul ready
INFO  jepsen.core - Worker 0 starting
INFO  jepsen.core - Worker 2 starting
INFO  jepsen.core - Worker 1 starting
INFO  jepsen.core - Worker 3 starting
INFO  jepsen.core - Worker 4 starting
INFO  jepsen.util - 2	:invoke	:read	nil
INFO  jepsen.util - 3	:invoke	:cas	[4 4]
INFO  jepsen.util - 0	:invoke	:write	4
INFO  jepsen.util - 1	:invoke	:write	1
INFO  jepsen.util - 4	:invoke	:cas	[4 0]
INFO  jepsen.util - 2	:ok	:read	nil
INFO  jepsen.util - 4	:fail	:cas	[4 0]
(Log Truncated...)
INFO  jepsen.util - 4	:invoke	:cas	[3 3]
INFO  jepsen.util - 4	:fail	:cas	[3 3]
INFO  jepsen.util - :nemesis	:info	:stop	nil
INFO  jepsen.util - :nemesis	:info	:stop	"fully connected"
INFO  jepsen.util - 0	:fail	:read	nil
INFO  jepsen.util - 1	:fail	:write	0
INFO  jepsen.util - :nemesis	:info	:stop	nil
INFO  jepsen.util - :nemesis	:info	:stop	"fully connected"
INFO  jepsen.core - nemesis done
INFO  jepsen.core - Worker 3 done
INFO  jepsen.util - 1	:invoke	:read	nil
INFO  jepsen.core - Worker 2 done
INFO  jepsen.core - Worker 4 done
INFO  jepsen.core - Worker 0 done
INFO  jepsen.util - 1	:ok	:read	3
INFO  jepsen.core - Worker 1 done
INFO  jepsen.core - Run complete, writing
INFO  jepsen.core - Analyzing
(Log Truncated...)
INFO  jepsen.core - Analysis complete
INFO  jepsen.system.consul - :n3 consul nuked
INFO  jepsen.system.consul - :n2 consul nuked
INFO  jepsen.system.consul - :n4 consul nuked
INFO  jepsen.system.consul - :n1 consul nuked
INFO  jepsen.system.consul - :n5 consul nuked
1964 element history linearizable. :D

Ran 1 tests containing 1 assertions.
0 failures, 0 errors.
```

<!--googleon: all-->