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Discovery Chain HTTP Endpoint

1.6.0+: The discovery chain API is available in Consul versions 1.6.0 and newer.

This is a low-level API primarily targeted at developers building external service mesh proxy integrations. Future high-level proxy integration APIs may obviate the need for this API over time.

The /discovery-chain endpoint returns the compiled discovery chain for a service.

This will fetch all related configuration entries and render them into a form suitable for use by a service mesh proxy implementation. This is a key component of L7 Traffic Management.

Read Compiled Discovery Chain

If overrides are needed they are passed as the JSON-encoded request body and the POST method must be used, otherwise GET is sufficient.

MethodPathProduces
GET/discovery-chain/:service_nameapplication/json
POST1/discovery-chain/:service_nameapplication/json

1 Both GET and POST are for read operations. GET requests do not permit request bodies so a POST is required if override parameters are needed.

The table below shows this endpoint's support for blocking queries, consistency modes, agent caching, and required ACLs.

Blocking QueriesConsistency ModesAgent CachingACL Required
YESallbackground refreshservice:read

Path Parameters

  • service_name (string: <required>) - Specifies the service to query when compiling the discovery chain.

Query Parameters

  • compile-dc (string: "") - Specifies the datacenter to use as the basis of compilation. This will default to the datacenter of the agent being queried.

    This value comes from the datacenter parameter in an upstream configuration.

  • ns (string: "") Enterprise - Specifies the source namespace you use as the basis of compilation. You can also specify the namespace through other methods.

JSON Request Body Schema

  • OverrideConnectTimeout (duration: 0s) - Overrides the final connect timeout for any service resolved in the compiled chain.

    This value comes from the connect_timeout_ms key in the opaque config field of the upstream configuration.

  • OverrideProtocol (string: "") - Overrides the final protocol used in the compiled discovery chain.

    If the chain ordinarily would be TCP and an L7 protocol is passed here the chain will still not include Routers or Splitters. If the chain ordinarily would be L7 and TCP is passed here the chain will not include Routers or Splitters.

    This value comes from the protocol key in an opaque config field of the upstream configuration.

  • OverrideMeshGateway (MeshGatewayConfig: <optional>) - Overrides the final mesh gateway configuration for this any service resolved in the compiled chain.

    This value comes from the mesh_gateway parameter in either the proxy configuration or upstream configuration If both parameters are configured, Consul uses the value defined on the upstream.

    • Mode (string: "") - One of none, local, or remote.

Sample Compilations

Full documentation for the output fields is found on the discovery chain internals page.

Multi-Datacenter Failover

Config entries defined:

kind            = "service-resolver"
name            = "web"
connect_timeout = "15s"
failover = {
  "*" = {
    datacenters = ["dc3", "dc4"]
  }
}

Request:

$ curl http://127.0.0.1:8500/v1/discovery-chain/web

Response:

{
  "Chain": {
    "ServiceName": "web",
    "Namespace": "default",
    "Datacenter": "dc1",
    "Protocol": "tcp",
    "StartNode": "resolver:web.default.dc1",
    "Nodes": {
      "resolver:web.default.dc1": {
        "Type": "resolver",
        "Name": "web.default.dc1",
        "Resolver": {
          "ConnectTimeout": "15s",
          "Target": "web.default.dc1",
          "Failover": {
            "Targets": ["web.default.dc3", "web.default.dc4"]
          }
        }
      }
    },
    "Targets": {
      "web.default.dc1": {
        "ID": "web.default.dc1",
        "Service": "web",
        "Namespace": "default",
        "Datacenter": "dc1",
        "MeshGateway": {},
        "Subset": {},
        "SNI": "web.default.dc1.internal.47e25151-6212-ba25-8b7e-81adbbbab461.consul",
        "Name": "web.default.dc1.internal.47e25151-6212-ba25-8b7e-81adbbbab461.consul"
      },
      "web.default.dc3": {
        "ID": "web.default.dc3",
        "Service": "web",
        "Namespace": "default",
        "Datacenter": "dc3",
        "MeshGateway": {},
        "Subset": {},
        "SNI": "web.default.dc3.internal.47e25151-6212-ba25-8b7e-81adbbbab461.consul",
        "Name": "web.default.dc3.internal.47e25151-6212-ba25-8b7e-81adbbbab461.consul"
      },
      "web.default.dc4": {
        "ID": "web.default.dc4",
        "Service": "web",
        "Namespace": "default",
        "Datacenter": "dc4",
        "MeshGateway": {},
        "Subset": {},
        "SNI": "web.default.dc4.internal.47e25151-6212-ba25-8b7e-81adbbbab461.consul",
        "Name": "web.default.dc4.internal.47e25151-6212-ba25-8b7e-81adbbbab461.consul"
      }
    }
  }
}

Datacenter Redirect with Overrides

Config entries defined:

kind            = "service-resolver"
name            = "web"
redirect {
  datacenter = "dc2"
}

Request:

$ curl --request POST \
    --data '
{
    "OverrideConnectTimeout": "7s",
    "OverrideProtocol": "grpc",
    "OverrideMeshGateway": {
        "Mode": "remote"
    }
}
' http://127.0.0.1:8500/v1/discovery-chain/web

Response:

{
  "Chain": {
    "ServiceName": "web",
    "Namespace": "default",
    "Datacenter": "dc1",
    "CustomizationHash": "b94f529a",
    "Protocol": "grpc",
    "StartNode": "resolver:web.default.dc2",
    "Nodes": {
      "resolver:web.default.dc2": {
        "Type": "resolver",
        "Name": "web.default.dc2",
        "Resolver": {
          "ConnectTimeout": "7s",
          "Target": "web.default.dc2"
        }
      }
    },
    "Targets": {
      "web.default.dc2": {
        "ID": "web.default.dc2",
        "Service": "web",
        "Namespace": "default",
        "Datacenter": "dc2",
        "MeshGateway": {
          "Mode": "remote"
        },
        "Subset": {},
        "SNI": "web.default.dc2.internal.59c17fd4-8dfa-f54a-ae71-855b26faf637.consul",
        "Name": "web.default.dc2.internal.59c17fd4-8dfa-f54a-ae71-855b26faf637.consul"
      }
    }
  }
}

Version Split For Alternate Datacenter

Config entries defined:

kind           = "service-resolver"
name           = "web"
default_subset = "v1"
subsets = {
  "v1" = {
    filter = "Service.Meta.version == v1"
  }
  "v2" = {
    filter = "Service.Meta.version == v2"
  }
}
# ---------------------------
kind = "service-defaults"
name = "web"
protocol = "http"
# ---------------------------
kind = "service-splitter"
name = "web"
splits = [
  {
    weight         = 90
    service_subset = "v1"
  },
  {
    weight         = 10
    service_subset = "v2"
  },
]

Request:

$ curl http://127.0.0.1:8500/v1/discovery-chain/web?compile-dc=dc2

Response:

{
  "Chain": {
    "ServiceName": "web",
    "Namespace": "default",
    "Datacenter": "dc2",
    "Protocol": "http",
    "StartNode": "splitter:web",
    "Nodes": {
      "resolver:v1.web.default.dc2": {
        "Type": "resolver",
        "Name": "v1.web.default.dc2",
        "Resolver": {
          "ConnectTimeout": "5s",
          "Target": "v1.web.default.dc2"
        }
      },
      "resolver:v2.web.default.dc2": {
        "Type": "resolver",
        "Name": "v2.web.default.dc2",
        "Resolver": {
          "ConnectTimeout": "5s",
          "Target": "v2.web.default.dc2"
        }
      },
      "splitter:web": {
        "Type": "splitter",
        "Name": "web",
        "Splits": [
          {
            "Weight": 90,
            "NextNode": "resolver:v1.web.default.dc2"
          },
          {
            "Weight": 10,
            "NextNode": "resolver:v2.web.default.dc2"
          }
        ]
      }
    },
    "Targets": {
      "v1.web.default.dc2": {
        "ID": "v1.web.default.dc2",
        "Service": "web",
        "ServiceSubset": "v1",
        "Namespace": "default",
        "Datacenter": "dc2",
        "MeshGateway": {},
        "Subset": {
          "Filter": "Service.Meta.version == v1"
        },
        "SNI": "v1.web.default.dc2.internal.6c9594ec-d798-28b9-d084-aa03e81cf078.consul",
        "Name": "v1.web.default.dc2.internal.6c9594ec-d798-28b9-d084-aa03e81cf078.consul"
      },
      "v2.web.default.dc2": {
        "ID": "v2.web.default.dc2",
        "Service": "web",
        "ServiceSubset": "v2",
        "Namespace": "default",
        "Datacenter": "dc2",
        "MeshGateway": {},
        "Subset": {
          "Filter": "Service.Meta.version == v2"
        },
        "SNI": "v2.web.default.dc2.internal.6c9594ec-d798-28b9-d084-aa03e81cf078.consul",
        "Name": "v2.web.default.dc2.internal.6c9594ec-d798-28b9-d084-aa03e81cf078.consul"
      }
    }
  }
}

HTTP Path Routing

Config entries defined:

kind           = "service-resolver"
name           = "web"
subsets = {
  "canary" = {
    filter = "Service.Meta.flavor == canary"
  }
}
# ---------------------------
kind = "proxy-defaults"
name = "web"
config {
  protocol = "http"
}
# ---------------------------
kind = "service-router"
name = "web"
routes = [
  {
    match {
      http {
        path_prefix = "/admin"
      }
    }
    destination {
      service         = "admin"
      prefix_rewrite  = "/"
      request_timeout = "15s"
    }
  },
  {
    match {
      http {
        header = [
          {
            name  = "x-debug"
            exact = "1"
          },
        ]
      }
    }
    destination {
      service                  = "web"
      service_subset           = "canary"
      num_retries              = 5
      retry_on_connect_failure = true
      retry_on_status_codes    = [401, 409]
    }
  },
]

Request:

$ curl http://127.0.0.1:8500/v1/discovery-chain/web

Response:

{
  "Chain": {
    "ServiceName": "web",
    "Namespace": "default",
    "Datacenter": "dc1",
    "Protocol": "http",
    "StartNode": "router:web",
    "Nodes": {
      "resolver:admin.default.dc1": {
        "Type": "resolver",
        "Name": "admin.default.dc1",
        "Resolver": {
          "ConnectTimeout": "5s",
          "Default": true,
          "Target": "admin.default.dc1"
        }
      },
      "resolver:canary.web.default.dc1": {
        "Type": "resolver",
        "Name": "canary.web.default.dc1",
        "Resolver": {
          "ConnectTimeout": "5s",
          "Target": "canary.web.default.dc1"
        }
      },
      "resolver:web.default.dc1": {
        "Type": "resolver",
        "Name": "web.default.dc1",
        "Resolver": {
          "ConnectTimeout": "5s",
          "Target": "web.default.dc1"
        }
      },
      "router:web": {
        "Type": "router",
        "Name": "web",
        "Routes": [
          {
            "Definition": {
              "Match": {
                "HTTP": {
                  "PathPrefix": "/admin"
                }
              },
              "Destination": {
                "RequestTimeout": "15s",
                "Service": "admin",
                "PrefixRewrite": "/"
              }
            },
            "NextNode": "resolver:admin.default.dc1"
          },
          {
            "Definition": {
              "Match": {
                "HTTP": {
                  "Header": [
                    {
                      "Name": "x-debug",
                      "Exact": "1"
                    }
                  ]
                }
              },
              "Destination": {
                "Service": "web",
                "ServiceSubset": "canary",
                "NumRetries": 5,
                "RetryOnConnectFailure": true,
                "RetryOnStatusCodes": [401, 409]
              }
            },
            "NextNode": "resolver:canary.web.default.dc1"
          },
          {
            "Definition": {
              "Match": {
                "HTTP": {
                  "PathPrefix": "/"
                }
              },
              "Destination": {
                "Service": "web"
              }
            },
            "NextNode": "resolver:web.default.dc1"
          }
        ]
      }
    },
    "Targets": {
      "admin.default.dc1": {
        "ID": "admin.default.dc1",
        "Service": "admin",
        "Namespace": "default",
        "Datacenter": "dc1",
        "MeshGateway": {},
        "Subset": {},
        "SNI": "admin.default.dc1.internal.fce8a058-0981-2c04-d23c-b7375af64ce8.consul",
        "Name": "admin.default.dc1.internal.fce8a058-0981-2c04-d23c-b7375af64ce8.consul"
      },
      "canary.web.default.dc1": {
        "ID": "canary.web.default.dc1",
        "Service": "web",
        "ServiceSubset": "canary",
        "Namespace": "default",
        "Datacenter": "dc1",
        "MeshGateway": {},
        "Subset": {
          "Filter": "Service.Meta.flavor == canary"
        },
        "SNI": "canary.web.default.dc1.internal.fce8a058-0981-2c04-d23c-b7375af64ce8.consul",
        "Name": "canary.web.default.dc1.internal.fce8a058-0981-2c04-d23c-b7375af64ce8.consul"
      },
      "web.default.dc1": {
        "ID": "web.default.dc1",
        "Service": "web",
        "Namespace": "default",
        "Datacenter": "dc1",
        "MeshGateway": {},
        "Subset": {},
        "SNI": "web.default.dc1.internal.fce8a058-0981-2c04-d23c-b7375af64ce8.consul",
        "Name": "web.default.dc1.internal.fce8a058-0981-2c04-d23c-b7375af64ce8.consul"
      }
    }
  }
}

Methods to specify namespace Enterprise

The discovery chain endpoint supports several methods for specifying the namespace to use as the basis of discovery chain compilation with the following order of precedence:

  1. ns query parameter
  2. X-Consul-Namespace request header
  3. Namespace is inherited from the namespace of the request's ACL token (if any)
  4. The default namespace
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