mirror of https://github.com/hashicorp/consul
55 lines
3.4 KiB
Markdown
55 lines
3.4 KiB
Markdown
---
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layout: docs
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page_title: Consul vs. Eureka
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description: >-
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Eureka is a service discovery tool that provides a best effort registry and
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discovery service. It uses central servers and clients which are typically
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natively integrated with SDKs. Consul provides a super set of features, such
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as health checking, key/value storage, ACLs, and multi-datacenter awareness.
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---
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# Consul vs. Eureka
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Eureka is a service discovery tool. The architecture is primarily client/server,
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with a set of Eureka servers per datacenter, usually one per availability zone.
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Typically clients of Eureka use an embedded SDK to register and discover services.
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For clients that are not natively integrated, a sidecar such as Ribbon is used
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to transparently discover services via Eureka.
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Eureka provides a weakly consistent view of services, using best effort replication.
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When a client registers with a server, that server will make an attempt to replicate
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to the other servers but provides no guarantee. Service registrations have a short
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Time-To-Live (TTL), requiring clients to heartbeat with the servers. Unhealthy services
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or nodes will stop heartbeating, causing them to timeout and be removed from the registry.
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Discovery requests can route to any service, which can serve stale or missing data due to
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the best effort replication. This simplified model allows for easy cluster administration
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and high scalability.
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Consul provides a super set of features, including richer health checking, key/value store,
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and multi-datacenter awareness. Consul requires a set of servers in each datacenter, along
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with an agent on each client, similar to using a sidecar like Ribbon. The Consul agent allows
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most applications to be Consul unaware, performing the service registration via configuration
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files and discovery via DNS or load balancer sidecars.
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Consul provides a strong consistency guarantee, since servers replicate state using the
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[Raft protocol](/docs/architecture/consensus). Consul supports a rich set of health checks
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including TCP, HTTP, Nagios/Sensu compatible scripts, or TTL based like Eureka. Client nodes
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participate in a [gossip based health check](/docs/architecture/gossip), which distributes
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the work of health checking, unlike centralized heartbeating which becomes a scalability challenge.
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Discovery requests are routed to the elected Consul leader which allows them to be strongly consistent
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by default. Clients that allow for stale reads enable any server to process their request allowing
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for linear scalability like Eureka.
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The strongly consistent nature of Consul means it can be used as a locking service for leader
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elections and cluster coordination. Eureka does not provide similar guarantees, and typically
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requires running ZooKeeper for services that need to perform coordination or have stronger
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consistency needs.
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Consul provides a toolkit of features needed to support a service oriented architecture.
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This includes service discovery, but also rich health checking, locking, Key/Value, multi-datacenter
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federation, an event system, and ACLs. Both Consul and the ecosystem of tools like consul-template
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and envconsul try to minimize application changes required to integration, to avoid needing
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native integration via SDKs. Eureka is part of a larger Netflix OSS suite, which expects applications
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to be relatively homogeneous and tightly integrated. As a result, Eureka only solves a limited
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subset of problems, expecting other tools such as ZooKeeper to be used alongside.
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