Merge pull request #3126 from hashicorp/doc-eureka

website: Add a vs Eureka. Fixes #1295

website/source/intro/vs/eureka.html.md

@@ -0,0 +1,53 @@
+---
+layout: "intro"
+page_title: "Consul vs. Eureka"
+sidebar_current: "vs-other-eureka"
+description: |-
+  Eureka is a service discovery tool that provides a best effort registry and discovery service. It uses central servers and clients which are typically natively integrated with SDKs. Consul provides a super set of features, such as health checking, key/value storage, ACLs, and multi-datacenter awareness.
+---
+
+# Consul vs. Eureka
+
+Eureka is a service discovery tool. The architecture is primarily client/server,
+with a set of Eureka servers per datacenter, usually one per availability zone.
+Typically clients of Eureka use an embedded SDK to register and discover services.
+For clients that are not natively integrated, a sidecar such as Ribbon is used
+to transparently discover services via Eureka.
+
+Eureka provides a weakly consistent view of services, using best effort replication.
+When a client registers with a server, that server will make an attempt to replicate
+to the other servers but provides no guarantee. Service registrations have a short
+Time-To-Live (TTL), requiring clients to heartbeat with the servers. Unhealthy services
+or nodes will stop heartbeating, causing them to timeout and be removed from the registry.
+Discovery requests can route to any service, which can serve stale or missing data due to
+the best effort replication. This simplified model allows for easy cluster administration
+and high scalability.
+
+Consul provides a super set of features, including richer health checking, key/value store,
+and multi-datacenter awareness. Consul requires a set of servers in each datacenter, along
+with an agent on each client, similar to using a sidecar like Ribbon. The Consul agent allows
+most applications to be Consul unaware, performing the service registration via configuration
+files and discovery via DNS or load balancer sidecars.
+
+Consul provides a strong consistency guarantee, since servers replicate state using the
+[Raft protocol](/docs/internals/consensus.html). Consul supports a rich set of health checks
+including TCP, HTTP, Nagios/Sensu compatible scripts, or TTL based like Eureka. Client nodes
+participate in a [gossip based health check](/docs/internals/gossip.html), which distributes
+the work of health checking, unlike centralized heartbeating which becomes a scalability challenge.
+Discovery requests are routed to the elected Consul leader which allows them to be strongly consistent
+by default. Clients that allow for stale reads enable any server to process their request allowing
+for linear scalability like Eureka.
+
+The strongly consistent nature of Consul means it can be used as a locking service for leader
+elections and cluster coordination. Eureka does not provide similar guarantees, and typically
+requires running ZooKeeper for services that need to perform coordination or have stronger
+consistency needs.
+
+Consul provides a toolkit of features needed to support a service oriented architecture.
+This includes service discovery, but also rich health checking, locking, Key/Value, multi-datacenter
+federation, an event system, and ACLs. Both Consul and the ecosystem of tools like consul-template
+and envconsul try to minimize application changes required to integration, to avoid needing
+native integration via SDKs. Eureka is part of a larger Netflix OSS suite, which expects applications
+to be relatively homogeneous and tightly integrated. As a result, Eureka only solves a limited
+subset of problems, expecting other tools such as ZooKeeper to be used alongside.
+

website/source/layouts/intro.erb

@@ -26,6 +26,9 @@
           <li<%= sidebar_current("vs-other-serf") %>>
             <a href="/intro/vs/serf.html">Serf</a>
           </li>
+          <li<%= sidebar_current("vs-other-eureka") %>>
+            <a href="/intro/vs/eureka.html">Eureka</a>
+          </li>
           <li<%= sidebar_current("vs-other-custom") %>>
             <a href="/intro/vs/custom.html">Custom Solutions</a>
           </li>