58 lines
3.1 KiB
Markdown
58 lines
3.1 KiB
Markdown
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---
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layout: "intro"
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page_title: "Terraform vs. SmartStack"
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sidebar_current: "vs-other-smartstack"
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---
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# Terraform vs. SmartStack
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SmartStack is another tool which tackles the service discovery problem.
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It has a rather unique architecture, and has 4 major components: ZooKeeper,
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HAProxy, Synapse, and Nerve. The ZooKeeper servers are responsible for storing cluster
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state in a consistent and fault tolerant manner. Each node in the SmartStack
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cluster then runs both Nerves and Synapses. The Nerve is responsible for running
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health checks against a service, and registering with the ZooKeeper servers.
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Synapse queries ZooKeeper for service providers and dynamically configures
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HAProxy. Finally, clients speak to HAProxy, which does health checking and
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load balancing across service providers.
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Terraform is a much simpler and more contained system, as it does not rely on any external
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components. Terraform uses an integrated [gossip protocol](/docs/internals/gossip.html)
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to track all nodes and perform server discovery. This means that server addresses
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do not need to be hardcoded and updated fleet wide on changes, unlike SmartStack.
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Service registration for both Terraform and Nerves can be done with a configuration file,
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but Terraform also supports an API to dynamically change the services and checks that are in use.
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For discovery, SmartStack clients must use HAProxy, requiring that Synapse be
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configured with all desired endpoints in advance. Terraform clients instead
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use the DNS or HTTP APIs without any configuration needed in advance. Terraform
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also provides a "tag" abstraction, allowing services to provide metadata such
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as versions, primary/secondary designations, or opaque labels that can be used for
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filtering. Clients can then request only the service providers which have
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matching tags.
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The systems also differ in how they manage health checking.
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Nerve's performs local health checks in a manner similar to Terraform agents.
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However, Terraform maintains separate catalog and health systems, which allow
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operators to see which nodes are in each service pool, as well as providing
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insight into failing checks. Nerve simply deregisters nodes on failed checks,
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providing limited operator insight. Synapse also configures HAProxy to perform
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additional health checks. This causes all potential service clients to check for
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liveness. With large fleets, this N-to-N style health checking may be prohibitively
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expensive.
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Terraform generally provides a much richer health checking system. Terraform supports
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Nagios style plugins, enabling a vast catalog of checks to be used. It also
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allows for service and host-level checks. There is also a "dead man's switch"
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check that allows applications to easily integrate custom health checks. All of this
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is also integrated into a Health and Catalog system with APIs enabling operator
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to gain insight into the broader system.
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In addition to the service discovery and health checking, Terraform also provides
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an integrated key/value store for configuration and multi-datacenter support.
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While it may be possible to configure SmartStack for multiple datacenters,
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the central ZooKeeper cluster would be a serious impediment to a fault tolerant
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deployment.
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