We've started our first agent and registered and queried a service on that agent. This showed how easy it is to use Consul but didn't show how this could be extended to a scalable, production-grade service discovery infrastructure. In this step, we'll create our first real cluster with multiple members.

When a Consul agent is started, it begins without knowledge of any other node: it is an isolated cluster of one. To learn about other cluster members, the agent must join an existing cluster. To join an existing cluster, it only needs to know about a single existing member. After it joins, the agent will gossip with this member and quickly discover the other members in the cluster. A Consul agent can join any other agent, not just agents in server mode.