Discover services on virtual machines (VMs)

This page provides an overview of Consul service discovery operations on virtual machines. After you register services with Consul, you can address them using Consul DNS to perform application load balancing and static service lookups. You can also create prepared queries for dynamic service lookups and service failover.

Introduction

When a service registers with Consul, the catalog records the address of each service's node. Consul then updates an instance's catalog entry with the results of each health check it performs. Consul agents replicate catalog information between each other using the Raft consensus protocol, enabling high availability service networking through any Consul agent.

Consul's service discovery operations use Consul DNS addresses to route traffic to healthy service instances and return information about service nodes registered to Consul.

Application load balancing

A load balancer accepts incoming traffic requests and routes them to service instances in a distributed network so that resource consumption is spread between available instances and individual nodes are not overworked. Consul functions as a load balancer by directing traffic to healthy service instances using information registered to the catalog and Consul DNS. Consul can also integrate with external load balancers such as NGINX and HAProxy.

Load balancing is a core component of Consul's service discovery functionality. For more information, refer to service discovery overview.

Static lookups

To lookup details about registered services and specific service instances, perform a static query using Consul DNS to return A and SRV records for your deployment. Consul DNS enables you to return results from across your Consul deployment, including the number of healthy instances and network addresses of nodes that match service names or custom tags.

Consul Enterprise enables static lookups for Enterprise features such as virtual services and sameness groups. Refer to Perform static DNS queries for more information.

Prepared queries

Prepared queries are configurations that enable you to register a complex service query and perform dynamic lookups on services using Consul DNS. Prepared queries enable advanced lookup scenarios such filtering by multiple tags and returning services that match a prefix. You can also use prepared queries to implement service failover scenarios between datacenters.

For more information, refer to Perform dynamic service lookups with prepared queries.

Tutorials

To get started with Consul's service discovery features on VMs, refer to the following tutorials:

• Register your services to Consul

Reference documentation

For reference material related to Consul's service discovery functions, refer to the following pages:

• Consul DNS reference

Constraints, limitations, and troubleshooting

If you experience errors when using Consul's service discovery features, refer to the following list of technical constraints.

• Consul's DNS and service discovery features are enabled by default. When Consul service mesh is enabled, you can use an existing DNS such as CoreDNS by configuring Consul's transparent proxy. Refer to transparent proxy for more information.
• When Consul's service mesh is enabled, you can use configuration entries that have additional impacts on Consul's service discovery behavior:
  • You can customize Consul's load balancing policy using a service resolver configuration entry.
  • You can adjust the request rate for services using a service defaults configuration entry.