42 lines
2.0 KiB
Markdown
42 lines
2.0 KiB
Markdown
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---
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layout: "intro"
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page_title: "Terraform vs. SkyDNS"
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sidebar_current: "vs-other-skydns"
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---
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# Terraform vs. SkyDNS
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SkyDNS is a relatively new tool designed to solve service discovery.
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It uses multiple central servers that are strongly consistent and
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fault tolerant. Nodes register services using an HTTP API, and
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queries can be made over HTTP or DNS to perform discovery.
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Terraform is very similar, but provides a superset of features. Terraform
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also relies on multiple central servers to provide strong consistency
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and fault tolerance. Nodes can use an HTTP API or use an agent to
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register services, and queries are made over HTTP or DNS.
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However, the systems differ in many ways. Terraform provides a much richer
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health checking framework, with support for arbitrary checks and
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a highly scalable failure detection scheme. SkyDNS relies on naive
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heartbeating and TTLs, which have known scalability issues. Additionally,
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the heartbeat only provides a limited liveness check, versus the rich
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health checks that Terraform is capable of.
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Multiple datacenters can be supported by using "regions" in SkyDNS,
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however the data is managed and queried from a single cluster. If servers
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are split between datacenters the replication protocol will suffer from
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very long commit times. If all the SkyDNS servers are in a central datacenter, then
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connectivity issues can cause entire datacenters to lose availability.
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Additionally, even without a connectivity issue, query performance will
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suffer as requests must always be performed in a remote datacenter.
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Terraform supports multiple datacenters out of the box, and it purposely
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scopes the managed data to be per-datacenter. This means each datacenter
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runs an independent cluster of servers. Requests are forwarded to remote
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datacenters if necessary. This means requests for services within a datacenter
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never go over the WAN, and connectivity issues between datacenters do not
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affect availability within a datacenter. Additionally, the unavailability
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of one datacenter does not affect the service discovery of services
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in any other datacenter.
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