Common discovery API components¶

DiscoveryRequest¶

A DiscoveryRequest requests a set of versioned resources of the same type for a given Envoy node on some API.

{
  "version_info": "...",
  "node": "{...}",
  "resource_names": [],
  "type_url": "...",
  "response_nonce": "...",
  "error_detail": "{...}"
}

version_info: (string) The version_info provided in the request messages will be the version_info received with the most recent successfully processed response or empty on the first request. It is expected that no new request is sent after a response is received until the Envoy instance is ready to ACK/NACK the new configuration. ACK/NACK takes place by returning the new API config version as applied or the previous API config version respectively. Each type_url (see below) has an independent version associated with it.

node: (core.Node) The node making the request.

resource_names: (string) List of resources to subscribe to, e.g. list of cluster names or a route configuration name. If this is empty, all resources for the API are returned. LDS/CDS may have empty resource_names, which will cause all resources for the Envoy instance to be returned. The LDS and CDS responses will then imply a number of resources that need to be fetched via EDS/RDS, which will be explicitly enumerated in resource_names.

type_url: (string) Type of the resource that is being requested, e.g. “type.googleapis.com/envoy.api.v2.ClusterLoadAssignment”. This is implicit in requests made via singleton xDS APIs such as CDS, LDS, etc. but is required for ADS.

response_nonce: (string) nonce corresponding to DiscoveryResponse being ACK/NACKed. See above discussion on version_info and the DiscoveryResponse nonce comment. This may be empty only if 1) this is a non-persistent-stream xDS such as HTTP, or 2) the client has not yet accepted an update in this xDS stream (unlike delta, where it is populated only for new explicit ACKs).

error_detail: (Status) This is populated when the previous DiscoveryResponse failed to update configuration. The message field in error_details provides the Envoy internal exception related to the failure. It is only intended for consumption during manual debugging, the string provided is not guaranteed to be stable across Envoy versions.

DiscoveryResponse¶

[DiscoveryResponse proto]

{
  "version_info": "...",
  "resources": [],
  "type_url": "...",
  "nonce": "..."
}

version_info: (string) The version of the response data.

resources: (Any) The response resources. These resources are typed and depend on the API being called.

type_url: (string) Type URL for resources. Identifies the xDS API when muxing over ADS. Must be consistent with the type_url in the ‘resources’ repeated Any (if non-empty).

nonce: (string) For gRPC based subscriptions, the nonce provides a way to explicitly ack a specific DiscoveryResponse in a following DiscoveryRequest. Additional messages may have been sent by Envoy to the management server for the previous version on the stream prior to this DiscoveryResponse, that were unprocessed at response send time. The nonce allows the management server to ignore any further DiscoveryRequests for the previous version until a DiscoveryRequest bearing the nonce. The nonce is optional and is not required for non-stream based xDS implementations.

DeltaDiscoveryRequest¶

[DeltaDiscoveryRequest proto]

DeltaDiscoveryRequest and DeltaDiscoveryResponse are used in a new gRPC endpoint for Delta xDS.

With Delta xDS, the DeltaDiscoveryResponses do not need to include a full snapshot of the tracked resources. Instead, DeltaDiscoveryResponses are a diff to the state of a xDS client. In Delta XDS there are per-resource versions, which allow tracking state at the resource granularity. An xDS Delta session is always in the context of a gRPC bidirectional stream. This allows the xDS server to keep track of the state of xDS clients connected to it.

In Delta xDS the nonce field is required and used to pair DeltaDiscoveryResponse to a DeltaDiscoveryRequest ACK or NACK. Optionally, a response message level system_version_info is present for debugging purposes only.

DeltaDiscoveryRequest plays two independent roles. Any DeltaDiscoveryRequest can be either or both of: [1] informing the server of what resources the client has gained/lost interest in (using resource_names_subscribe and resource_names_unsubscribe), or [2] (N)ACKing an earlier resource update from the server (using response_nonce, with presence of error_detail making it a NACK). Additionally, the first message (for a given type_url) of a reconnected gRPC stream has a third role: informing the server of the resources (and their versions) that the client already possesses, using the initial_resource_versions field.

As with state-of-the-world, when multiple resource types are multiplexed (ADS), all requests/acknowledgments/updates are logically walled off by type_url: a Cluster ACK exists in a completely separate world from a prior Route NACK. In particular, initial_resource_versions being sent at the “start” of every gRPC stream actually entails a message for each type_url, each with its own initial_resource_versions.

{
  "node": "{...}",
  "type_url": "...",
  "resource_names_subscribe": [],
  "resource_names_unsubscribe": [],
  "initial_resource_versions": "{...}",
  "response_nonce": "...",
  "error_detail": "{...}"
}

node: (core.Node) The node making the request.

type_url: (string) Type of the resource that is being requested, e.g. “type.googleapis.com/envoy.api.v2.ClusterLoadAssignment”.

resource_names_unsubscribe: (string) A list of Resource names to remove from the list of tracked resources.

initial_resource_versions: (map<string, string>) Informs the server of the versions of the resources the xDS client knows of, to enable the client to continue the same logical xDS session even in the face of gRPC stream reconnection. It will not be populated: [1] in the very first stream of a session, since the client will not yet have any resources, [2] in any message after the first in a stream (for a given type_url), since the server will already be correctly tracking the client’s state. (In ADS, the first message of each type_url of a reconnected stream populates this map.) The map’s keys are names of xDS resources known to the xDS client. The map’s values are opaque resource versions.

response_nonce: (string) When the DeltaDiscoveryRequest is a ACK or NACK message in response to a previous DeltaDiscoveryResponse, the response_nonce must be the nonce in the DeltaDiscoveryResponse. Otherwise (unlike in DiscoveryRequest) response_nonce must be omitted.

error_detail: (Status) This is populated when the previous DiscoveryResponse failed to update configuration. The message field in error_details provides the Envoy internal exception related to the failure.

DeltaDiscoveryResponse¶

[DeltaDiscoveryResponse proto]

{
  "system_version_info": "...",
  "resources": [],
  "type_url": "...",
  "removed_resources": [],
  "nonce": "..."
}

system_version_info: (string) The version of the response data (used for debugging).

resources: (Resource) The response resources. These are typed resources, whose types must match the type_url field.

type_url: (string) Type URL for resources. Identifies the xDS API when muxing over ADS. Must be consistent with the type_url in the Any within ‘resources’ if ‘resources’ is non-empty.

removed_resources: (string) Resources names of resources that have be deleted and to be removed from the xDS Client. Removed resources for missing resources can be ignored.

nonce: (string) The nonce provides a way for DeltaDiscoveryRequests to uniquely reference a DeltaDiscoveryResponse when (N)ACKing. The nonce is required.

Resource¶

[Resource proto]

{
  "name": "...",
  "aliases": [],
  "version": "...",
  "resource": "{...}"
}

name: (string) The resource’s name, to distinguish it from others of the same type of resource.

aliases: (string) The aliases are a list of other names that this resource can go by.

version: (string) The resource level version. It allows xDS to track the state of individual resources.

resource: (Any) The resource being tracked.