Learn theLearn how Consul fits into the
Any infrastructure for any application
Service registry, integrated health checks, and DNS and HTTP interfaces enable any service to discover and be discovered by other services
Load balancers are often used to front a service tier and provide a static IP. These load balancers add cost, increase latency, introduce single points of failure, and must be updated as services scale up/down.
Instead of load balancers, connectivity in dynamic infrastructure is best solved with service discovery. Service discovery uses a registry to keep a real-time list of services, their location, and their health. Services query the registry to discover the location of upstream services and then connect directly. This allows services to scale up/down and gracefully handle failure without a load balancer intermediary.
Consul provides a registry of all the running nodes and services, along with their current health status. This allows operators to understand the environment, and applications and automation tools to interact with dynamic infrastructure using an HTTP API.
Consul enables service discovery using a built-in DNS server. This allows existing applications to easily integrate, as almost all applications support using DNS to resolve IP addresses. Using DNS instead of a static IP address allows services to scale up/down and route around failures easily.
Learn the HashiCorp Enterprise Suite 
$ dig web-frontend.service.consul. ANY
; <<>> DiG 9.8.3-P1 <<>> web-frontend.service.consul. ANY
;; global options: +cmd
;; Got answer:
;; ->>HEADER<<- opcode: QUERY, status: NOERROR, id: 29981
;; flags: qr aa rd ra; QUERY: 1, ANSWER: 2, AUTHORITY: 0, ADDITIONAL: 0
;; QUESTION SECTION:
;web-frontend.service.consul. IN ANY
;; ANSWER SECTION:
web-frontend.service.consul. 0 IN A 10.0.3.83
web-frontend.service.consul. 0 IN A 10.0.1.109
Consul provides an HTTP API to query the service registry for nodes, services, and health check information. The API also supports blocking queries, or long-polling for any changes. This allows automation tools to react to services being registered or health status changes to change configurations or traffic routing in real time.
$ curl http://localhost:8500/v1/health/service/web?index=11&wait=30s
{
...
"Node": "10-0-1-109",
"CheckID": "service:web",
"Name": "Service 'web' check",
"Status": "critical",
"ServiceID": "web",
"ServiceName": "web",
"CreateIndex": 10,
"ModifyIndex": 20
...
}
Consul supports multiple datacenters out of the box with no complicated configuration. Look up services in other datacenters or keep the request local. Advanced features like Prepared Queries enable automatic failover to other datacenters.
$ curl http://localhost:8500/v1/catalog/datacenters
[
"dc1",
"dc2"
]
$ curl http://localhost:8500/v1/catalog/nodes?dc=dc2
[
{
"ID": "7081dcdf-fdc0-0432-f2e8-a357d36084e1",
"Node": "10-0-1-109",
"Address": "10.0.1.109",
"Datacenter": "dc2",
"TaggedAddresses": {
"lan": "10.0.1.109",
"wan": "10.0.1.109"
},
"CreateIndex": 112,
"ModifyIndex": 125
},
...
Pairing service discovery with health checking prevents routing requests to unhealthy hosts and enables services to easily provide circuit breakers.
