Service Discovery

Consul is a service discovery technology that ensures microservices can communicate with each other.

Distinguishing features

Consul has some features that set it apart from other service discovery solutions.

HTTP REST API & DNS support

Consul has an HTTP REST API and supports DNS.

• DNS (Domain Name System) is the system that maps host names such as www.innoq.com to IP addresses on the Internet.
• In addition to returning IP addresses, it can return ports at which a service is available.
• This is a feature of the SRV DNS records.

Configuration file generation

With Consul Template, Consul can generate configuration files.

• The files may contain IP addresses and ports of services registered in Consul.
• Consul Template also provides Consul’s service discovery to systems that cannot access Consul via the API.
• The systems have to use some kind of configuration file, which they often already do anyway.

Health checks

Consul can perform health checks and exclude services from service discovery when the health check fails.

• For example, a health check can be a request to a specific HTTP resource to determine whether the service can still process requests.
• A service may still be able to accept HTTP requests, but it may not be able to process them properly due to a database failure.
• The service can signal this through the health check.

Replication

Consul supports replication and can ensure high availability.

If a Consul server fails, other servers with replicated data take over and compensate for the failed server.

Multiple data centers

Consul also supports multiple data centers.

• Data can be replicated between data centers to further increase availability and protect Consul against the failure of a data center.
• The search for services can be limited to the same data center.
• Services in the same data center usually deliver higher performance.

Service configuration

Finally, Consul can be used not only for service discovery, but for the configuration of services.

• Configuration has different requirements.

• Availability is important for service discovery.

• Faulty information can be tolerated.

• If the service is accessed and is not available, it doesn’t matter. You can simply use another instance of the service.

• However, if services are configured incorrectly, this can lead to errors.

• Correct information is more important for configuration than for service discovery.