consul

Grey Matter Control supports service discovery from HashiCorp Consul. For a working example, see examples/consul.

Consul and Service Configuration

To discover services using Consul, there are three specifications that must be met in the Consul configuration and specified in the configuration of gm-control.

Consul Agent

Each service must be registered with a Consul Agent. The Consul Agents should be running in the same cluster. For gm-control to recognize instance information such as node and/or service health, services should be registered with their own client node (agent). More information on running a Consul Agent can be found here. The cluster should be running at a known address to be specified in the gm-control configuration.

Datacenter

Consul services are collected by gm-control from a single specified datacenter, thus all services to be discovered by Consul must be registered in this datacenter. The datacenter is a also a part of the Consul Agent configuration.

NOTE The datacenter must be explicitly set using the command line flag --dc or environment variable GM_CONTROL_CONSUL_DC when running gm-control.

Service Tags

Services in Consul are discovered by gm-control using tags. All services to be discovered by gm-control must contain a matching service tag. Tags are specified in the service definition in the form of "tags": ["{chosen-tag}"]. Without this tag, services will be ignored by the control plane.

NOTE By default, this tag must be "gm-cluster" or can be otherwise specified to gm-control on the command line with the flag --cluster-tag.

Configure Grey Matter Control

The following three environment variables must be set in gm-control to discover services from Consul:

GM_CONTROL_CMD=consul
GM_CONTROL_CONSUL_DC={your-consul-datacenter}
GM_CONTROL_CONSUL_HOSTPORT={your-consul-host}:{your-consul-port}

GM_CONTROL_CONSUL_HOSTPORT must specify the address of your Consul cluster. As noted above, the datacenter can be specified here or with the command line flag --dc.

There is an optional environment variable, GM_CONTROL_XDS_RESOLVE_DNS, which should be set to true in order to resolve service DNS before passing the instance IPs to Envoy (as service instances will normally be registered as IP addresses). If you plan to use Envoy to route to hostname, make sure to set this flag.