open-consul/website/source/intro/index.html.md

---
layout: "intro"
page_title: "Introduction"
sidebar_current: "what"
description: |-
  Welcome to the intro guide to Consul! This guide is the best place to start with Consul. We cover what Consul is, what problems it can solve, how it compares to existing software, and how you can get started using it. If you are familiar with the basics of Consul, the documentation provides a more detailed reference of available features.
---

# Introduction to Consul

Welcome to the intro guide to Consul! This guide is the best place to start
with Consul. We cover what Consul is, what problems it can solve, how it compares
to existing software, and how you can get started using it. If you are familiar
with the basics of Consul, the [documentation](/docs/index.html) provides a more
detailed reference of available features.

## What is Consul?

Consul is a service mesh solution providing a full featured control plane
with service discovery, configuration, and segmentation functionality. Each
of these features can be used individually as needed, or they can be used
together to build a full service mesh. Consul requires a data plane and
supports both a proxy and native integration model. Consul ships with a
simple built-in proxy so that everything works out of the box, but also
supports 3rd party proxy integrations such as Envoy.

Review the video below to learn more about Consul from HashiCorp's co-founder Armon. 

<iframe src="https://www.youtube.com/embed/mxeMdl0KvBI" frameborder="0" allowfullscreen="true"  width="560" height="315" ></iframe>

The key features of Consul are:

* **Service Discovery**: Clients of Consul can register a service, such as
  `api` or `mysql`, and other clients can use Consul to discover providers
  of a given service. Using either DNS or HTTP, applications can easily find
  the services they depend upon.

* **Health Checking**: Consul clients can provide any number of health checks,
  either associated with a given service ("is the webserver returning 200 OK"), or
  with the local node ("is memory utilization below 90%"). This information can be
  used by an operator to monitor cluster health, and it is used by the service
  discovery components to route traffic away from unhealthy hosts.

* **KV Store**: Applications can make use of Consul's hierarchical key/value
  store for any number of purposes, including dynamic configuration, feature flagging,
  coordination, leader election, and more. The simple HTTP API makes it easy to use.

* **Secure Service Communication**: Consul can generate and distribute TLS
  certificates for services to establish mutual TLS connections.
  [Intentions](/docs/connect/intentions.html)
  can be used to define which services are allowed to communicate.
  Service segmentation can be easily managed with intentions that can
  be changed in real time instead of using complex network topologies
  and static firewall rules.

* **Multi Datacenter**: Consul supports multiple datacenters out of the box. This
  means users of Consul do not have to worry about building additional layers of
  abstraction to grow to multiple regions.

Consul is designed to be friendly to both the DevOps community and
application developers, making it perfect for modern, elastic infrastructures.

## Basic Architecture of Consul

Consul is a distributed, highly available system. This section will cover the
basics, purposely omitting some unnecessary detail, so you can get a quick
understanding of how Consul works. For more detail, please refer to the
[in-depth architecture overview](/docs/internals/architecture.html).

Every node that provides services to Consul runs a _Consul agent_. Running
an agent is not required for discovering other services or getting/setting
key/value data. The agent is responsible for health checking the services
on the node as well as the node itself.

The agents talk to one or more _Consul servers_. The Consul servers are
where data is stored and replicated. The servers themselves elect a leader.
While Consul can function with one server, 3 to 5 is recommended to avoid
failure scenarios leading to data loss. A cluster of Consul servers is recommended
for each datacenter.

The servers maintain a _catalog_, which is formed by aggregating information
submitted by the agents. The catalog maintains the high-level view of the cluster,
including which services are available, which nodes run those services, health 
information, and more. How agents and the catalog interact can be found 
[here](/docs/internals/anti-entropy.html#catalog).

Components of your infrastructure that need to discover other services
or nodes can query any of the Consul servers _or_ any of the Consul agents.
The agents forward queries to the servers automatically.

Each datacenter runs a cluster of Consul servers. When a cross-datacenter
service discovery or configuration request is made, the local Consul servers
forward the request to the remote datacenter and return the result.

## Next Steps

* See [how Consul compares to other software](/intro/vs/index.html) to assess how it fits into your
existing infrastructure.
* Continue onwards with the [getting started guide](https://learn.hashicorp.com/consul/getting-started/install)
to get Consul up and running.