Service Resolver

Service Resolver

1.6.0+: This config entry is available in Consul versions 1.6.0 and newer.

The service-resolver config entry kind controls which service instances should satisfy Connect upstream discovery requests for a given service name.

If no resolver config is defined the chain assumes 100% of traffic goes to the healthy instances of the default service in the current datacenter+namespace and discovery terminates.

Interaction with other Config Entries

Service resolver config entries are a component of L7 Traffic Management.

Sample Config Entries

Create service subsets based on a version metadata and override the defaults:

Kind          = "service-resolver"
Name          = "web"
DefaultSubset = "v1"
Subsets = {
  "v1" = {
    Filter = "Service.Meta.version == v1"
  }
  "v2" = {
    Filter = "Service.Meta.version == v2"
  }
}

Expose a set of services in another datacenter as a virtual service:

Kind = "service-resolver"
Name = "web-dc2"
Redirect {
  Service    = "web"
  Datacenter = "dc2"
}

Enable failover for all subsets:

Kind           = "service-resolver"
Name           = "web"
ConnectTimeout = "15s"
Failover = {
  "*" = {
    Datacenters = ["dc3", "dc4"]
  }
}

Representation of the defaults when a resolver is not configured:

Kind = "service-resolver"
Name = "web"

Available Fields

Kind - Must be set to service-resolver
Name (string: <required>) - Set to the name of the service being configured.
Namespace (string: "default")

Enterprise

- Specifies the namespace the config entry will apply to.
Meta (map<string|string>: nil) - Specifies arbitrary KV metadata pairs. Added in Consul 1.8.4.
ConnectTimeout (duration: 0s) - The timeout for establishing new network connections to this service.
DefaultSubset (string: "") - The subset to use when no explicit subset is requested. If empty the unnamed subset is used.
Subsets (map[string]ServiceResolverSubset) - A map of subset name to subset definition for all usable named subsets of this service. The map key is the name of the subset and all names must be valid DNS subdomain elements.

This may be empty, in which case only the unnamed default subset will be usable.
- Filter (string: "") - The filter expression to be used for selecting instances of the requested service. If empty all healthy instances are returned. This expression can filter on the same selectors as the Health API endpoint.
- OnlyPassing (bool: false) - Specifies the behavior of the resolver’s health check interpretation. If this is set to false, instances with checks in the passing as well as the warning states will be considered healthy. If this is set to true, only instances with checks in the passing state will be considered healthy.
Redirect (ServiceResolverRedirect: <optional>) - When configured, all attempts to resolve the service this resolver defines will be substituted for the supplied redirect EXCEPT when the redirect has already been applied.

When substituting the supplied redirect into the all other fields besides Kind, Name, and Redirect will be ignored.
- Service (string: "") - A service to resolve instead of the current service.
- ServiceSubset (string: "") - A named subset of the given service to resolve instead of one defined as that service’s DefaultSubset If empty the default subset is used.
```
If this is specified at least one of Service, Datacenter, or Namespace
should be configured.
```
- Namespace (string: "") - The namespace to resolve the service from instead of the current one.
- Datacenter (string: "") - The datacenter to resolve the service from instead of the current one.
Failover (map[string]ServiceResolverFailover) - Controls when and how to reroute traffic to an alternate pool of service instances.

The map is keyed by the service subset it applies to and the special string "*" is a wildcard that applies to any subset not otherwise specified here.

Service, ServiceSubset, Namespace, and Datacenters cannot all be empty at once.
- Service (string: "") - The service to resolve instead of the default as the failover group of instances during failover.
- ServiceSubset (string: "") - The named subset of the requested service to resolve as the failover group of instances. If empty the default subset for the requested service is used.
- Namespace (string: "") - The namespace to resolve the requested service from to form the failover group of instances. If empty the current namespace is used.
- Datacenters (array<string>) - A fixed list of datacenters to try during failover.

Service Subsets

A service subset assigns a concrete name to a specific subset of discoverable service instances within a datacenter, such as "version2" or "canary".

A service subset name is useful only when composed with an actual service name, a specific datacenter, and namespace.

All services have an unnamed default subset that will return all healthy instances unfiltered.

Subsets are defined in service-resolver configuration entries, but are referenced by their names throughout the other configuration entry kinds.

ACLs

Configuration entries may be protected by ACLs.

Reading a service-resolver config entry requires service:read on itself.

Creating, updating, or deleting a service-resolver config entry requires service:write on itself and service:read on any other service referenced by name in these fields:

Redirect.Service
Failover[].Service