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Remove outdated usage of "Consul Connect" instead of Consul service mesh. The connect subsystem in Consul provides Consul's service mesh capabilities. However, the term "Consul Connect" should not be used as an alternative to the name "Consul service mesh".
250 lines
11 KiB
Plaintext
250 lines
11 KiB
Plaintext
---
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layout: docs
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page_title: Service Mesh Traffic Management - Discovery Chain
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description: >-
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The discovery chain compiles service router, splitter, and resolver configuration entries to direct traffic to specific instances in a service mesh. Learn about compiled discovery chain results, including discovery graph nodes and targets.
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---
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# Discovery Chain for Service Mesh Traffic Management
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-> **1.6.0+:** This feature is available in Consul versions 1.6.0 and newer.
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~> This topic is part of a [low-level API](/consul/api-docs/discovery-chain)
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primarily targeted at developers building external [Consul service mesh proxy
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integrations](/consul/docs/connect/proxies/integrate).
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The service discovery process can be modeled as a "discovery chain" which
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passes through three distinct stages: routing, splitting, and resolution. Each
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of these stages is controlled by a set of [configuration
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entries](/consul/docs/agent/config-entries). By configuring different phases of
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the discovery chain a user can control how proxy upstreams are ultimately
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resolved to specific instances for load balancing.
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-> **Note:** The discovery chain is currently only used to discover
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[service mesh](/consul/docs/connect) proxy upstreams.
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## Configuration
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The configuration entries used in the discovery chain are designed to be simple
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to read and modify for narrowly tailored changes, but at discovery-time the
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various configuration entries interact in more complex ways. For example:
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- If a [`service-resolver`](/consul/docs/connect/config-entries/service-resolver)
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is created with a [service
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redirect](/consul/docs/connect/config-entries/service-resolver#service) defined,
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then all references made to the original service in any other configuration
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entry is replaced with the redirect destination.
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- If a [`service-resolver`](/consul/docs/connect/config-entries/service-resolver)
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is created with a [default
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subset](/consul/docs/connect/config-entries/service-resolver#defaultsubset)
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defined then all references made to the original service in any other
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configuration entry that did not specify a subset will be replaced with the
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default.
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- If a [`service-splitter`](/consul/docs/connect/config-entries/service-splitter)
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is created with a [service
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split](/consul/docs/connect/config-entries/service-splitter#splits), and the target service has its
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own `service-splitter` then the overall effect is flattened and only a single
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aggregate traffic split is ultimately configured in the proxy.
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- [`service-resolver`](/consul/docs/connect/config-entries/service-resolver)
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redirect loops must be rejected as invalid.
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- [`service-router`](/consul/docs/connect/config-entries/service-router) and
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[`service-splitter`](/consul/docs/connect/config-entries/service-splitter)
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configuration entries require an L7 compatible protocol be set for the
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service via either a
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[`service-defaults`](/consul/docs/connect/config-entries/service-defaults) or
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[`proxy-defaults`](/consul/docs/connect/config-entries/proxy-defaults) config
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entry. Violations must be rejected as invalid.
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- If an [upstream
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configuration](/consul/docs/connect/registration/service-registration#upstream-configuration-reference)
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[`datacenter`](/consul/docs/connect/registration/service-registration#datacenter)
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parameter is defined then any configuration entry that does not explicitly
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refer to a desired datacenter should use that value from the upstream.
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## Compilation
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To correctly interpret a collection of configuration entries as a valid
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discovery chain, we first compile them into a form more directly usable by the
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layers responsible for configuring service mesh sidecar proxies.
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You can interact with the compiler directly using the [discovery-chain
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API](/consul/api-docs/discovery-chain).
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### Compilation Parameters
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- **Service Name** - The service being discovered by name.
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- **Datacenter** - The datacenter to use as the basis of compilation.
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- **Overrides** - Discovery-time tweaks to apply when compiling. These should
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be derived from either the
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[proxy](/consul/docs/connect/registration/service-registration#complete-configuration-example)
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or
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[upstream](/consul/docs/connect/registration/service-registration#upstream-configuration-reference)
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configurations if either are set.
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### Compilation Results
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The response is a single wrapped `CompiledDiscoveryChain` field:
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```json
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{
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"Chain": {...<CompiledDiscoveryChain>...}
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}
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```
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#### `CompiledDiscoveryChain`
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The chain encodes a digraph of [nodes](#discoverygraphnode) and
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[targets](#discoverytarget). Nodes are the compiled representation of various
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discovery chain stages and targets are instructions on how to use the [health
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API](/consul/api-docs/health#list-nodes-for-mesh-capable-service) to retrieve
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relevant service instance lists.
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You should traverse the nodes starting with [`StartNode`](#startnode). The
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nodes can be resolved by name using the [`Nodes`](#nodes) field. Targets can be
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resolved by name using the [`Targets`](#targets) field.
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- `ServiceName` `(string)` - The requested service.
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- `Partition` `(string)` - The requested partition.
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- `Namespace` `(string)` - The requested namespace.
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- `Datacenter` `(string)` - The requested datacenter.
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- `CustomizationHash` `(string: <optional>)` - A unique hash of any overrides
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that affected the compilation of the discovery chain.
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If set, this value should be used to prefix/suffix any generated load
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balancer data plane objects to avoid sharing customized and non-customized
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versions.
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- `Default` `(bool: <optional>)` - Indicates if this discovery chain is based on no
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`service-resolver`, `service-splitter`, or `service-router` config entries.
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- `Protocol` `(string)` - The overall protocol shared by everything in the
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chain.
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- `ServiceMeta` `(map<string|string>)` - The metadata from the underlying `service-defaults` config
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entry for the service named `ServiceName`.
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- `StartNode` `(string)` - The first key into the `Nodes` map that should be
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followed when traversing the discovery chain.
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- `Nodes` `(map<string|DiscoveryGraphNode>)` - All nodes available for traversal in
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the chain keyed by a unique name. You can walk this by starting with
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`StartNode`.
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-> The names should be treated as opaque values and are only guaranteed to be
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consistent within a single compilation.
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- `Targets` `(map<string|DiscoveryTarget>)` - A list of all targets used in this chain.
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-> The names should be treated as opaque values and are only guaranteed to be
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consistent within a single compilation.
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#### `DiscoveryGraphNode`
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A single node in the compiled discovery chain.
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- `Type` `(string)` - The type of the node. Valid values are: `router`,
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`splitter`, and `resolver`.
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- `Name` `(string)` - The unique name of the node.
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- `Routes` `(array<DiscoveryRoute>)` - Only set for `Type:router`. List of routes to
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render.
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- `Definition` `(ServiceRoute)` - Relevant portion of underlying
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`service-router`
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[route](/consul/docs/connect/config-entries/service-router#routes).
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- `NextNode` `(string)` - The name of the next node in the chain in [`Nodes`](#nodes).
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- `Splits` `(array<DiscoverySplit>)` - Only set for `Type:splitter`. List of traffic
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splits.
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- `Weight` `(float32)` - Copy of underlying `service-splitter`
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[`weight`](/consul/docs/connect/config-entries/service-splitter#weight) field.
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- `NextNode` `(string)` - The name of the next node in the chain in [`Nodes`](#nodes).
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- `Resolver` `(DiscoveryResolver: <optional>)` - Only set for `Type:resolver`. How
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to resolve the service instances.
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- `Default` `(bool)` - Set to true if no `service-resolver` config entry is
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defined for this node and the default was synthesized.
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- `ConnectTimeout` `(duration)` - Copy of the underlying `service-resolver`
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[`ConnectTimeout`](/consul/docs/connect/config-entries/service-resolver#connecttimeout)
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field. If one is not defined the default of `5s` is returned.
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- `Target` `(string)` - The name of the target to use found in [`Targets`](#targets).
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- `Failover` `(DiscoveryFailover: <optional>)` - Compiled form of the
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underlying `service-resolver`
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[`Failover`](/consul/docs/connect/config-entries/service-resolver#failover)
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definition to use for this request.
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- `Targets` `(array<string>)` - List of targets found in
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[`Targets`](#targets) to failover to in order of preference.
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- `LoadBalancer` `(LoadBalancer: <optional>`) - Copy of the underlying `service-resolver`
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[`LoadBalancer`](/consul/docs/connect/config-entries/service-resolver#loadbalancer) field.
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If a `service-splitter` splits between services with differing `LoadBalancer` configuration
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the first hash-based load balancing policy is copied.
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#### `DiscoveryTarget`
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- `ID` `(string)` - The unique name of this target.
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- `Service` `(string)` - The service to query when resolving a list of service instances.
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- `ServiceSubset` `(string: <optional>)` - The
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[subset](/consul/docs/connect/config-entries/service-resolver#service-subsets) of
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the service to resolve.
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- `Partition` `(string)` - The partition to use when resolving a list of service instances.
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- `Namespace` `(string)` - The namespace to use when resolving a list of service instances.
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- `Datacenter` `(string)` - The datacenter to use when resolving a list of service instances.
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- `Subset` `(ServiceResolverSubset)` - Copy of the underlying
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`service-resolver`
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[`Subsets`](/consul/docs/connect/config-entries/service-resolver#subsets)
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definition for this target.
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- `Filter` `(string: "")` - The
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[filter expression](/consul/api-docs/features/filtering) to be used for selecting
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instances of the requested service. If empty all healthy instances are
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returned.
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- `OnlyPassing` `(bool: false)` - Specifies the behavior of the resolver's
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health check interpretation. If this is set to false, instances with checks
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in the passing as well as the warning states will be considered healthy. If
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this is set to true, only instances with checks in the passing state will
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be considered healthy.
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- `MeshGateway` `(MeshGatewayConfig)` - The [mesh gateway
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configuration](/consul/docs/connect/gateways/mesh-gateway#service-mesh-proxy-configuration)
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to use when connecting to this target's service instances.
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- `Mode` `(string: "")` - One of `none`, `local`, or `remote`.
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- `External` `(bool: false)` - True if this target is outside of this consul cluster.
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- `ConnectTimeout` `(duration)` - Copy of the underlying `service-resolver`
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[`ConnectTimeout`](/consul/docs/connect/config-entries/service-resolver#connecttimeout)
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field. If one is not defined the default of `5s` is returned.
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- `SNI` `(string)` - This value should be used as the
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[SNI](https://en.wikipedia.org/wiki/Server_Name_Indication) value when
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connecting to this set of endpoints over TLS.
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- `Name` `(string)` - The unique name for this target for use when generating
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load balancer objects. This has a structure similar to [SNI](#sni), but will
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not be affected by SNI customizations such as
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[`ExternalSNI`](/consul/docs/connect/config-entries/service-defaults#externalsni).
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