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Include information about multi-dc Connect

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Erik R. Rygg 2019-01-08 14:30:36 -07:00
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website/source/docs/guides/deployment.html.md
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@ -70,12 +70,18 @@ A typical use case is where datacenter1 (dc1) hosts share services like LDAP (or
Network areas allows peering between datacenters to make the services discoverable over WAN. With network areas, servers in dc1 can communicate with those in dc2 and dc3. However, no connectivity needs to be established between dc2 and dc3 which meets the compliance requirement of the organization in this use case. Servers that are part of the network area communicate over RPC only. This removes the overhead of sharing and maintaining the symmetric key used by the gossip protocol across datacenters. It also reduces the attack surface at the gossip ports since they no longer need to be opened in security gateways or firewalls.
#### Prepared Queries
Consul’s [prepared queries](/api/query.html) allow clients to do a datacenter failover for service discovery. For example, if a service `payment` in the local datacenter dc1 goes down, a prepared query lets users define a geographic fallback order to the nearest datacenter to check for healthy instances of the same service.
~> **NOTE** Consul clusters must be WAN linked for a prepared query to work across datacenters.
Prepared queries, by default, resolve the query in the local datacenter first. Querying KV store features is not supported by the prepared query. Prepared queries work with ACL. Prepared query config/templates are maintained consistently in Raft and are executed on the servers.
#### Connect
Consul [Connect](/docs/guides/connect-production.html) supports multi-datacenter connections and replicates [intentions](/docs/connect/intentions.html). This allows WAN federated DCs to provide connections from source and destination proxies in any DC.
## Network Connectivity
LAN gossip occurs between all agents in a single datacenter with each agent sending a periodic probe to random agents from its member list. Agents run in either client or server mode, both participate in the gossip. The initial probe is sent over UDP every second. If a node fails to acknowledge within `200ms`, the agent pings over TCP. If the TCP probe fails (10 second timeout), it asks configurable number of random nodes to probe the same node (also known as an indirect probe). If there is no response from the peers regarding the status of the node, that agent is marked as down.