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