43 lines
2.1 KiB
Plaintext
43 lines
2.1 KiB
Plaintext
---
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layout: docs
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page_title: 'Consul vs. Nagios'
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description: >-
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Nagios is a tool built for monitoring. It is used to quickly
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notify operators when an issue occurs.
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---
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# Consul vs. Nagios
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Nagios is a tool built for monitoring. It is used to quickly notify
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operators when an issue occurs.
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Nagios uses a group of central servers that are configured to perform
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checks on remote hosts. This design makes it difficult to scale Nagios,
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as large fleets quickly reach the limit of vertical scaling, and Nagios
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does not easily scale horizontally. Nagios is also notoriously
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difficult to use with modern DevOps and configuration management tools,
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as local configurations must be updated when remote servers are added
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or removed.
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Consul provides the same health checking abilities as Nagios,
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is friendly to modern DevOps, and avoids the inherent scaling issues.
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Consul runs all checks locally, avoiding placing a burden on central servers.
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The status of checks is maintained by the Consul servers, which are fault
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tolerant and have no single point of failure. Lastly, Consul can scale to
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vastly more checks because it relies on edge-triggered updates. This means
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that an update is only triggered when a check transitions from "passing"
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to "failing" or vice versa.
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In a large fleet, the majority of checks are passing, and even the minority
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that are failing are persistent. By capturing changes only, Consul reduces
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the amount of networking and compute resources used by the health checks,
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allowing the system to be much more scalable.
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An astute reader may notice that if a Consul agent dies, then no edge triggered
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updates will occur. From the perspective of other nodes, all checks will appear
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to be in a steady state. However, Consul guards against this as well. The
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[gossip protocol](/docs/internals/gossip) used between clients and servers
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integrates a distributed failure detector. This means that if a Consul agent fails,
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the failure will be detected, and thus all checks being run by that node can be
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assumed failed. This failure detector distributes the work among the entire cluster
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while, most importantly, enabling the edge triggered architecture to work. |