--- layout: api page_title: Discovery Chain - HTTP API sidebar_title: Discovery Chain description: The /discovery-chain endpoints are for interacting with the discovery chain. --- -> **1.6.0+:** The discovery chain API is available in Consul versions 1.6.0 and newer. # Discovery Chain HTTP Endpoint ~> This is a low-level API primarily targeted at developers building external [Connect proxy integrations](/docs/connect/proxies/integrate). Future high-level proxy integration APIs may obviate the need for this API over time. The `/discovery-chain` endpoint returns the compiled [discovery chain](/docs/internals/discovery-chain) for a service. This will fetch all related [configuration entries](/docs/agent/config_entries) and render them into a form suitable for use by a [connect proxy](/docs/connect/proxies) implementation. This is a key component of [L7 Traffic Management](/docs/connect/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. | Method | Path | Produces | | ------------------ | --------------------------- | ------------------ | | `GET` | `/discovery-chain/:service` | `application/json` | | `POST`1 | `/discovery-chain/:service` | `application/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](/api/features/blocking), [consistency modes](/api/features/consistency), [agent caching](/api/features/caching), and [required ACLs](/api#authentication). | Blocking Queries | Consistency Modes | Agent Caching | ACL Required | | ---------------- | ----------------- | -------------------- | -------------- | | `YES` | `all` | `background refresh` | `service:read` | ### URL Parameters - `service` `(string: )` - Specifies the service to query when compiling the discovery chain. This is provided as part of the URL. - `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 is specified as part of the URL as a query parameter. This value comes from an [upstream configuration](/docs/connect/registration/service-registration#upstream-configuration-reference) [`datacenter`](/docs/connect/registration/service-registration#datacenter) parameter. ### POST Body Parameters - `OverrideConnectTimeout` `(duration: 0s)` - Overrides the final [connect timeout](/docs/agent/config-entries/service-resolver#connecttimeout) for any service resolved in the compiled chain. This value comes from the `connect_timeout_ms` key in an [upstream configuration](/docs/connect/registration/service-registration#upstream-configuration-reference) opaque [`config`](/docs/connect/registration/service-registration#config-1) parameter. - `OverrideProtocol` `(string: "")` - Overrides the final [protocol](/docs/agent/config-entries/service-defaults#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 [upstream configuration](/docs/connect/registration/service-registration#upstream-configuration-reference) opaque [`config`](/docs/connect/registration/service-registration#config-1) parameter. - `OverrideMeshGateway` `(MeshGatewayConfig: )` - Overrides the final [mesh gateway configuration](/docs/connect/mesh-gateway#connect-proxy-configuration) for this any service resolved in the compiled chain. This value comes from either the [proxy configuration](/docs/connect/registration/service-registration#complete-configuration-example) [`mesh_gateway`](/docs/connect/registration/service-registration#mesh_gateway) parameter or an [upstream configuration](/docs/connect/registration/service-registration#upstream-configuration-reference) [`mesh_gateway`](/docs/connect/registration/service-registration#mesh_gateway-1) parameter. If both are present the value defined on the upstream is used. - `Mode` `(string: "")` - One of `none`, `local`, or `remote`. ### Sample Compilations Full documentation for the output fields is found on the [discovery chain internals](/docs/internals/discovery-chain#compileddiscoverychain) page. #### Multi-Datacenter Failover Config entries defined: ```hcl kind = "service-resolver" name = "web" connect_timeout = "15s" failover = { "*" = { datacenters = ["dc3", "dc4"] } } ``` Request: ```shell-session $ curl http://127.0.0.1:8500/v1/discovery-chain/web ``` Response: ```json { "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: ```hcl kind = "service-resolver" name = "web" redirect { datacenter = "dc2" } ``` Request: ```shell-session $ curl -X POST \ -d' { "OverrideConnectTimeout": "7s", "OverrideProtocol": "grpc", "OverrideMeshGateway": { "Mode": "remote" } } ' http://127.0.0.1:8500/v1/discovery-chain/web ``` Response: ```json { "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: ```hcl 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: ```shell-session $ curl http://127.0.0.1:8500/v1/discovery-chain/web?compile-dc=dc2 ``` Response: ```json { "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: ```hcl 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: ```shell-session $ curl http://127.0.0.1:8500/v1/discovery-chain/web ``` Response: ```json { "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" } } } } ```