47 lines
2.4 KiB
Markdown
47 lines
2.4 KiB
Markdown
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---
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layout: "intro"
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page_title: "Terraform vs. Serf"
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sidebar_current: "vs-other-serf"
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---
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# Terraform vs. Serf
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[Serf](http://www.serfdom.io) is a node discovery and orchestration tool and is the only
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tool discussed so far that is built on an eventually consistent gossip model,
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with no centralized servers. It provides a number of features, including group
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membership, failure detection, event broadcasts and a query mechanism. However,
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Serf does not provide any high-level features such as service discovery, health
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checking or key/value storage. To clarify, the discovery feature of Serf is at a node
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level, while Terraform provides a service and node level abstraction.
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Terraform is a complete system providing all of those features. In fact, the internal
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[gossip protocol](/docs/internals/gossip.html) used within Terraform, is powered by
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the Serf library. Terraform leverages the membership and failure detection features,
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and builds upon them.
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The health checking provided by Serf is very low level, and only indicates if the
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agent is alive. Terraform extends this to provide a rich health checking system,
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that handles liveness, in addition to arbitrary host and service-level checks.
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Health checks are integrated with a central catalog that operators can easily
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query to gain insight into the cluster.
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The membership provided by Serf is at a node level, while Terraform focuses
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on the service level abstraction, with a single node to multiple service model.
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This can be simulated in Serf using tags, but it is much more limited, and does
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not provide useful query interfaces. Terraform also makes use of a strongly consistent
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Catalog, while Serf is only eventually consistent.
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In addition to the service level abstraction and improved health checking,
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Terraform provides a key/value store and support for multiple datacenters.
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Serf can run across the WAN but with degraded performance. Terraform makes use
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of [multiple gossip pools](/docs/internals/architecture.html), so that
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the performance of Serf over a LAN can be retained while still using it over
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a WAN for linking together multiple datacenters.
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Terraform is opinionated in its usage, while Serf is a more flexible and
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general purpose tool. Terraform uses a CP architecture, favoring consistency over
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availability. Serf is a AP system, and sacrifices consistency for availability.
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This means Terraform cannot operate if the central servers cannot form a quorum,
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while Serf will continue to function under almost all circumstances.
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