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balancer.go
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balancer.go
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/*
*
* Copyright 2017 gRPC authors.
*
* Licensed under the Apache License, Version 2.0 (the "License");
* you may not use this file except in compliance with the License.
* You may obtain a copy of the License at
*
* http://www.apache.org/licenses/LICENSE-2.0
*
* Unless required by applicable law or agreed to in writing, software
* distributed under the License is distributed on an "AS IS" BASIS,
* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
* See the License for the specific language governing permissions and
* limitations under the License.
*
*/
// Package balancer defines APIs for load balancing in gRPC.
// All APIs in this package are experimental.
package balancer
import (
"context"
"encoding/json"
"errors"
"net"
"strings"
"github.com/hxx258456/ccgo/grpc/connectivity"
"github.com/hxx258456/ccgo/grpc/credentials"
"github.com/hxx258456/ccgo/grpc/internal"
"github.com/hxx258456/ccgo/grpc/metadata"
"github.com/hxx258456/ccgo/grpc/resolver"
"github.com/hxx258456/ccgo/grpc/serviceconfig"
)
var (
// m is a map from name to balancer builder.
m = make(map[string]Builder)
)
// Register registers the balancer builder to the balancer map. b.Name
// (lowercased) will be used as the name registered with this builder. If the
// Builder implements ConfigParser, ParseConfig will be called when new service
// configs are received by the resolver, and the result will be provided to the
// Balancer in UpdateClientConnState.
//
// NOTE: this function must only be called during initialization time (i.e. in
// an init() function), and is not thread-safe. If multiple Balancers are
// registered with the same name, the one registered last will take effect.
func Register(b Builder) {
m[strings.ToLower(b.Name())] = b
}
// unregisterForTesting deletes the balancer with the given name from the
// balancer map.
//
// This function is not thread-safe.
func unregisterForTesting(name string) {
delete(m, name)
}
func init() {
internal.BalancerUnregister = unregisterForTesting
}
// Get returns the resolver builder registered with the given name.
// Note that the compare is done in a case-insensitive fashion.
// If no builder is register with the name, nil will be returned.
func Get(name string) Builder {
if b, ok := m[strings.ToLower(name)]; ok {
return b
}
return nil
}
// A SubConn represents a single connection to a gRPC backend service.
//
// Each SubConn contains a list of addresses.
//
// All SubConns start in IDLE, and will not try to connect. To trigger the
// connecting, Balancers must call Connect. If a connection re-enters IDLE,
// Balancers must call Connect again to trigger a new connection attempt.
//
// gRPC will try to connect to the addresses in sequence, and stop trying the
// remainder once the first connection is successful. If an attempt to connect
// to all addresses encounters an error, the SubConn will enter
// TRANSIENT_FAILURE for a backoff period, and then transition to IDLE.
//
// Once established, if a connection is lost, the SubConn will transition
// directly to IDLE.
//
// This interface is to be implemented by gRPC. Users should not need their own
// implementation of this interface. For situations like testing, any
// implementations should embed this interface. This allows gRPC to add new
// methods to this interface.
type SubConn interface {
// UpdateAddresses updates the addresses used in this SubConn.
// gRPC checks if currently-connected address is still in the new list.
// If it's in the list, the connection will be kept.
// If it's not in the list, the connection will gracefully closed, and
// a new connection will be created.
//
// This will trigger a state transition for the SubConn.
//
// Deprecated: This method is now part of the ClientConn interface and will
// eventually be removed from here.
UpdateAddresses([]resolver.Address)
// Connect starts the connecting for this SubConn.
Connect()
}
// NewSubConnOptions contains options to create new SubConn.
type NewSubConnOptions struct {
// CredsBundle is the credentials bundle that will be used in the created
// SubConn. If it's nil, the original creds from grpc DialOptions will be
// used.
//
// Deprecated: Use the Attributes field in resolver.Address to pass
// arbitrary data to the credential handshaker.
CredsBundle credentials.Bundle
// HealthCheckEnabled indicates whether health check service should be
// enabled on this SubConn
HealthCheckEnabled bool
}
// State contains the balancer's state relevant to the gRPC ClientConn.
type State struct {
// State contains the connectivity state of the balancer, which is used to
// determine the state of the ClientConn.
ConnectivityState connectivity.State
// Picker is used to choose connections (SubConns) for RPCs.
Picker Picker
}
// ClientConn represents a gRPC ClientConn.
//
// This interface is to be implemented by gRPC. Users should not need a
// brand new implementation of this interface. For the situations like
// testing, the new implementation should embed this interface. This allows
// gRPC to add new methods to this interface.
type ClientConn interface {
// NewSubConn is called by balancer to create a new SubConn.
// It doesn't block and wait for the connections to be established.
// Behaviors of the SubConn can be controlled by options.
NewSubConn([]resolver.Address, NewSubConnOptions) (SubConn, error)
// RemoveSubConn removes the SubConn from ClientConn.
// The SubConn will be shutdown.
RemoveSubConn(SubConn)
// UpdateAddresses updates the addresses used in the passed in SubConn.
// gRPC checks if the currently connected address is still in the new list.
// If so, the connection will be kept. Else, the connection will be
// gracefully closed, and a new connection will be created.
//
// This will trigger a state transition for the SubConn.
UpdateAddresses(SubConn, []resolver.Address)
// UpdateState notifies gRPC that the balancer's internal state has
// changed.
//
// gRPC will update the connectivity state of the ClientConn, and will call
// Pick on the new Picker to pick new SubConns.
UpdateState(State)
// ResolveNow is called by balancer to notify gRPC to do a name resolving.
ResolveNow(resolver.ResolveNowOptions)
// Target returns the dial target for this ClientConn.
//
// Deprecated: Use the Target field in the BuildOptions instead.
Target() string
}
// BuildOptions contains additional information for Build.
type BuildOptions struct {
// DialCreds is the transport credentials to use when communicating with a
// remote load balancer server. Balancer implementations which do not
// communicate with a remote load balancer server can ignore this field.
DialCreds credentials.TransportCredentials
// CredsBundle is the credentials bundle to use when communicating with a
// remote load balancer server. Balancer implementations which do not
// communicate with a remote load balancer server can ignore this field.
CredsBundle credentials.Bundle
// Dialer is the custom dialer to use when communicating with a remote load
// balancer server. Balancer implementations which do not communicate with a
// remote load balancer server can ignore this field.
Dialer func(context.Context, string) (net.Conn, error)
// Authority is the server name to use as part of the authentication
// handshake when communicating with a remote load balancer server. Balancer
// implementations which do not communicate with a remote load balancer
// server can ignore this field.
Authority string
// ChannelzParentID is the parent ClientConn's channelz ID.
ChannelzParentID int64
// CustomUserAgent is the custom user agent set on the parent ClientConn.
// The balancer should set the same custom user agent if it creates a
// ClientConn.
CustomUserAgent string
// Target contains the parsed address info of the dial target. It is the
// same resolver.Target as passed to the resolver. See the documentation for
// the resolver.Target type for details about what it contains.
Target resolver.Target
}
// Builder creates a balancer.
type Builder interface {
// Build creates a new balancer with the ClientConn.
Build(cc ClientConn, opts BuildOptions) Balancer
// Name returns the name of balancers built by this builder.
// It will be used to pick balancers (for example in service config).
Name() string
}
// ConfigParser parses load balancer configs.
type ConfigParser interface {
// ParseConfig parses the JSON load balancer config provided into an
// internal form or returns an error if the config is invalid. For future
// compatibility reasons, unknown fields in the config should be ignored.
ParseConfig(LoadBalancingConfigJSON json.RawMessage) (serviceconfig.LoadBalancingConfig, error)
}
// PickInfo contains additional information for the Pick operation.
type PickInfo struct {
// FullMethodName is the method name that NewClientStream() is called
// with. The canonical format is /service/Method.
FullMethodName string
// Ctx is the RPC's context, and may contain relevant RPC-level information
// like the outgoing header metadata.
Ctx context.Context
}
// DoneInfo contains additional information for done.
type DoneInfo struct {
// Err is the rpc error the RPC finished with. It could be nil.
Err error
// Trailer contains the metadata from the RPC's trailer, if present.
Trailer metadata.MD
// BytesSent indicates if any bytes have been sent to the server.
BytesSent bool
// BytesReceived indicates if any byte has been received from the server.
BytesReceived bool
// ServerLoad is the load received from server. It's usually sent as part of
// trailing metadata.
//
// The only supported type now is *orca_v1.LoadReport.
ServerLoad interface{}
}
var (
// ErrNoSubConnAvailable indicates no SubConn is available for pick().
// gRPC will block the RPC until a new picker is available via UpdateState().
ErrNoSubConnAvailable = errors.New("no SubConn is available")
// ErrTransientFailure indicates all SubConns are in TransientFailure.
// WaitForReady RPCs will block, non-WaitForReady RPCs will fail.
//
// Deprecated: return an appropriate error based on the last resolution or
// connection attempt instead. The behavior is the same for any non-gRPC
// status error.
ErrTransientFailure = errors.New("all SubConns are in TransientFailure")
)
// PickResult contains information related to a connection chosen for an RPC.
type PickResult struct {
// SubConn is the connection to use for this pick, if its state is Ready.
// If the state is not Ready, gRPC will block the RPC until a new Picker is
// provided by the balancer (using ClientConn.UpdateState). The SubConn
// must be one returned by ClientConn.NewSubConn.
SubConn SubConn
// Done is called when the RPC is completed. If the SubConn is not ready,
// this will be called with a nil parameter. If the SubConn is not a valid
// type, Done may not be called. May be nil if the balancer does not wish
// to be notified when the RPC completes.
Done func(DoneInfo)
}
// TransientFailureError returns e. It exists for backward compatibility and
// will be deleted soon.
//
// Deprecated: no longer necessary, picker errors are treated this way by
// default.
func TransientFailureError(e error) error { return e }
// Picker is used by gRPC to pick a SubConn to send an RPC.
// Balancer is expected to generate a new picker from its snapshot every time its
// internal state has changed.
//
// The pickers used by gRPC can be updated by ClientConn.UpdateState().
type Picker interface {
// Pick returns the connection to use for this RPC and related information.
//
// Pick should not block. If the balancer needs to do I/O or any blocking
// or time-consuming work to service this call, it should return
// ErrNoSubConnAvailable, and the Pick call will be repeated by gRPC when
// the Picker is updated (using ClientConn.UpdateState).
//
// If an error is returned:
//
// - If the error is ErrNoSubConnAvailable, gRPC will block until a new
// Picker is provided by the balancer (using ClientConn.UpdateState).
//
// - If the error is a status error (implemented by the grpc/status
// package), gRPC will terminate the RPC with the code and message
// provided.
//
// - For all other errors, wait for ready RPCs will wait, but non-wait for
// ready RPCs will be terminated with this error's Error() string and
// status code Unavailable.
Pick(info PickInfo) (PickResult, error)
}
// Balancer takes input from gRPC, manages SubConns, and collects and aggregates
// the connectivity states.
//
// It also generates and updates the Picker used by gRPC to pick SubConns for RPCs.
//
// UpdateClientConnState, ResolverError, UpdateSubConnState, and Close are
// guaranteed to be called synchronously from the same goroutine. There's no
// guarantee on picker.Pick, it may be called anytime.
type Balancer interface {
// UpdateClientConnState is called by gRPC when the state of the ClientConn
// changes. If the error returned is ErrBadResolverState, the ClientConn
// will begin calling ResolveNow on the active name resolver with
// exponential backoff until a subsequent call to UpdateClientConnState
// returns a nil error. Any other errors are currently ignored.
UpdateClientConnState(ClientConnState) error
// ResolverError is called by gRPC when the name resolver reports an error.
ResolverError(error)
// UpdateSubConnState is called by gRPC when the state of a SubConn
// changes.
UpdateSubConnState(SubConn, SubConnState)
// Close closes the balancer. The balancer is not required to call
// ClientConn.RemoveSubConn for its existing SubConns.
Close()
}
// ExitIdler is an optional interface for balancers to implement. If
// implemented, ExitIdle will be called when ClientConn.Connect is called, if
// the ClientConn is idle. If unimplemented, ClientConn.Connect will cause
// all SubConns to connect.
//
// Notice: it will be required for all balancers to implement this in a future
// release.
type ExitIdler interface {
// ExitIdle instructs the LB policy to reconnect to backends / exit the
// IDLE state, if appropriate and possible. Note that SubConns that enter
// the IDLE state will not reconnect until SubConn.Connect is called.
ExitIdle()
}
// SubConnState describes the state of a SubConn.
type SubConnState struct {
// ConnectivityState is the connectivity state of the SubConn.
ConnectivityState connectivity.State
// ConnectionError is set if the ConnectivityState is TransientFailure,
// describing the reason the SubConn failed. Otherwise, it is nil.
ConnectionError error
}
// ClientConnState describes the state of a ClientConn relevant to the
// balancer.
type ClientConnState struct {
ResolverState resolver.State
// The parsed load balancing configuration returned by the builder's
// ParseConfig method, if implemented.
BalancerConfig serviceconfig.LoadBalancingConfig
}
// ErrBadResolverState may be returned by UpdateClientConnState to indicate a
// problem with the provided name resolver data.
var ErrBadResolverState = errors.New("bad resolver state")
// ConnectivityStateEvaluator takes the connectivity states of multiple SubConns
// and returns one aggregated connectivity state.
//
// It's not thread safe.
type ConnectivityStateEvaluator struct {
numReady uint64 // Number of addrConns in ready state.
numConnecting uint64 // Number of addrConns in connecting state.
numTransientFailure uint64 // Number of addrConns in transient failure state.
numIdle uint64 // Number of addrConns in idle state.
}
// RecordTransition records state change happening in subConn and based on that
// it evaluates what aggregated state should be.
//
// - If at least one SubConn in Ready, the aggregated state is Ready;
// - Else if at least one SubConn in Connecting, the aggregated state is Connecting;
// - Else if at least one SubConn is TransientFailure, the aggregated state is Transient Failure;
// - Else if at least one SubConn is Idle, the aggregated state is Idle;
// - Else there are no subconns and the aggregated state is Transient Failure
//
// Shutdown is not considered.
func (cse *ConnectivityStateEvaluator) RecordTransition(oldState, newState connectivity.State) connectivity.State {
// Update counters.
for idx, state := range []connectivity.State{oldState, newState} {
updateVal := 2*uint64(idx) - 1 // -1 for oldState and +1 for new.
switch state {
case connectivity.Ready:
cse.numReady += updateVal
case connectivity.Connecting:
cse.numConnecting += updateVal
case connectivity.TransientFailure:
cse.numTransientFailure += updateVal
case connectivity.Idle:
cse.numIdle += updateVal
}
}
// Evaluate.
if cse.numReady > 0 {
return connectivity.Ready
}
if cse.numConnecting > 0 {
return connectivity.Connecting
}
if cse.numTransientFailure > 0 {
return connectivity.TransientFailure
}
if cse.numIdle > 0 {
return connectivity.Idle
}
return connectivity.TransientFailure
}