45 lines
2.3 KiB
Markdown
45 lines
2.3 KiB
Markdown
---
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layout: "docs"
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page_title: "Gossip Protocol"
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sidebar_current: "docs-internals-gossip"
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---
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# Gossip Protocol
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Consul uses a [gossip protocol](http://en.wikipedia.org/wiki/Gossip_protocol)
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to manage membership and broadcast messages to the cluster. All of this is provided
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through the use of the [Serf library](http://www.serfdom.io/). The gossip protocol
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used by Serf is based on
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["SWIM: Scalable Weakly-consistent Infection-style Process Group Membership Protocol"](http://www.cs.cornell.edu/~asdas/research/dsn02-swim.pdf),
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with a few minor adaptations. There are more details about [Serf's protocol here](http://www.serfdom.io/docs/internals/gossip.html).
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<div class="alert alert-block alert-warning">
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<strong>Advanced Topic!</strong> This page covers technical details of
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the internals of Consul. You don't need to know these details to effectively
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operate and use Consul. These details are documented here for those who wish
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to learn about them without having to go spelunking through the source code.
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</div>
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## Gossip in Consul
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Consul makes use of two different gossip pools. We refer to each pool as the
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LAN or WAN pool respectively. Each datacenter Consul operates in has a LAN gossip pool
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containing all members of the datacenter, both clients and servers. The LAN pool is
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used for a few purposes. Membership information allows clients to automatically discover
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servers, reducing the amount of configuration needed. The distributed failure detection
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allows the work of failure detection to be shared by the entire cluster instead of
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concentrated on a few servers. Lastly, the gossip pool allows for reliable and fast
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event broadcasts for events like leader election.
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The WAN pool is globally unique, as all servers should participate in the WAN pool
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regardless of datacenter. Membership information provided by the WAN pool allows
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servers to perform cross datacenter requests. The integrated failure detection
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allows Consul to gracefully handle an entire datacenter losing connectivity, or just
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a single server in a remote datacenter.
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All of these features are provided by leveraging [Serf](http://www.serfdom.io/). It
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is used as an embedded library to provide these features. From a user perspective,
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this is not important, since the abstraction should be masked by Consul. It can be useful
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however as a developer to understand how this library is leveraged.
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