Package io.envoyproxy.envoy.service.discovery.v2

Class HealthDiscoveryServiceGrpc.HealthDiscoveryServiceStub

  • Enclosing class:
    HealthDiscoveryServiceGrpc
    public static final class HealthDiscoveryServiceGrpc.HealthDiscoveryServiceStub
extends io.grpc.stub.AbstractAsyncStub<HealthDiscoveryServiceGrpc.HealthDiscoveryServiceStub>
     HDS is Health Discovery Service. It compliments Envoy’s health checking
 service by designating this Envoy to be a healthchecker for a subset of hosts
 in the cluster. The status of these health checks will be reported to the
 management server, where it can be aggregated etc and redistributed back to
 Envoy through EDS.

    • Method Detail

      • streamHealthCheck

        public io.grpc.stub.StreamObserver<HealthCheckRequestOrEndpointHealthResponse> streamHealthCheck​(io.grpc.stub.StreamObserver<HealthCheckSpecifier> responseObserver)
         1. Envoy starts up and if its can_healthcheck option in the static
    bootstrap config is enabled, sends HealthCheckRequest to the management
    server. It supplies its capabilities (which protocol it can health check
    with, what zone it resides in, etc.).
 2. In response to (1), the management server designates this Envoy as a
    healthchecker to health check a subset of all upstream hosts for a given
    cluster (for example upstream Host 1 and Host 2). It streams
    HealthCheckSpecifier messages with cluster related configuration for all
    clusters this Envoy is designated to health check. Subsequent
    HealthCheckSpecifier message will be sent on changes to:
    a. Endpoints to health checks
    b. Per cluster configuration change
 3. Envoy creates a health probe based on the HealthCheck config and sends
    it to endpoint(ip:port) of Host 1 and 2. Based on the HealthCheck
    configuration Envoy waits upon the arrival of the probe response and
    looks at the content of the response to decide whether the endpoint is
    healthy or not. If a response hasn't been received within the timeout
    interval, the endpoint health status is considered TIMEOUT.
 4. Envoy reports results back in an EndpointHealthResponse message.
    Envoy streams responses as often as the interval configured by the
    management server in HealthCheckSpecifier.
 5. The management Server collects health statuses for all endpoints in the
    cluster (for all clusters) and uses this information to construct
    EndpointDiscoveryResponse messages.
 6. Once Envoy has a list of upstream endpoints to send traffic to, it load
    balances traffic to them without additional health checking. It may
    use inline healthcheck (i.e. consider endpoint UNHEALTHY if connection
    failed to a particular endpoint to account for health status propagation
    delay between HDS and EDS).
 By default, can_healthcheck is true. If can_healthcheck is false, Cluster
 configuration may not contain HealthCheck message.
 TODO(htuch): How is can_healthcheck communicated to CDS to ensure the above
 invariant?
 TODO(htuch): Add @amb67's diagram.

      • fetchHealthCheck

        public void fetchHealthCheck​(HealthCheckRequestOrEndpointHealthResponse request,
                             io.grpc.stub.StreamObserver<HealthCheckSpecifier> responseObserver)
         TODO(htuch): Unlike the gRPC version, there is no stream-based binding of
 request/response. Should we add an identifier to the HealthCheckSpecifier
 to bind with the response?