balancer

Documentation

Overview

Package balancer defines APIs for load balancing in gRPC. All APIs in this package are experimental.

Index

• Variables
• func Register(b Builder)
• func TransientFailureError(err error) error
• type Balancer
• type BuildOptions
• type Builder
  • func Get(name string) Builder
• type ClientConn
• type ClientConnState
• type ConfigParser
• type ConnectivityStateEvaluator
  • func (cse *ConnectivityStateEvaluator) RecordTransition(oldState, newState connectivity.State) connectivity.State
• type DoneInfo
• type NewSubConnOptions
• type PickInfo
• type PickResult
• type Picker
• type State
• type SubConn
• type SubConnState
• type V2Balancer
• type V2Picker

Variables

var (
	// ErrNoSubConnAvailable indicates no SubConn is available for pick().
	// gRPC will block the RPC until a new picker is available via UpdateBalancerState().
	ErrNoSubConnAvailable = errors.New("no SubConn is available")
	// ErrTransientFailure indicates all SubConns are in TransientFailure.
	// WaitForReady RPCs will block, non-WaitForReady RPCs will fail.
	ErrTransientFailure = TransientFailureError(errors.New("all SubConns are in TransientFailure"))
)

var ErrBadResolverState = errors.New("bad resolver state")

ErrBadResolverState may be returned by UpdateClientConnState to indicate a problem with the provided name resolver data.

Functions

func Register

func Register(b 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 TransientFailureError

func TransientFailureError(err error) error

TransientFailureError wraps err in an error implementing IsTransientFailure() bool, returning true.

Types

type Balancer

type Balancer interface {
	// HandleSubConnStateChange is called by gRPC when the connectivity state
	// of sc has changed.
	// Balancer is expected to aggregate all the state of SubConn and report
	// that back to gRPC.
	// Balancer should also generate and update Pickers when its internal state has
	// been changed by the new state.
	//
	// Deprecated: if V2Balancer is implemented by the Balancer,
	// UpdateSubConnState will be called instead.
	HandleSubConnStateChange(sc SubConn, state connectivity.State)
	// HandleResolvedAddrs is called by gRPC to send updated resolved addresses to
	// balancers.
	// Balancer can create new SubConn or remove SubConn with the addresses.
	// An empty address slice and a non-nil error will be passed if the resolver returns
	// non-nil error to gRPC.
	//
	// Deprecated: if V2Balancer is implemented by the Balancer,
	// UpdateClientConnState will be called instead.
	HandleResolvedAddrs([]resolver.Address, error)
	// Close closes the balancer. The balancer is not required to call
	// ClientConn.RemoveSubConn for its existing SubConns.
	Close()
}

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.

HandleSubConnectionStateChange, HandleResolvedAddrs 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 BuildOptions

type BuildOptions struct {
	// DialCreds is the transport credential the Balancer implementation can
	// use to dial to a remote load balancer server. The Balancer implementations
	// can ignore this if it does not need to talk to another party securely.
	DialCreds credentials.TransportCredentials
	// CredsBundle is the credentials bundle that the Balancer can use.
	CredsBundle credentials.Bundle
	// Dialer is the custom dialer the Balancer implementation can use to dial
	// to a remote load balancer server. The Balancer implementations
	// can ignore this if it doesn't need to talk to remote balancer.
	Dialer func(context.Context, string) (net.Conn, error)
	// ChannelzParentID is the entity parent's channelz unique identification number.
	ChannelzParentID int64
	// 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
}

BuildOptions contains additional information for Build.

type Builder

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
}

Builder creates a balancer.

func Get

func Get(name string) Builder

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.

type ClientConn

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)

	// UpdateBalancerState is called by balancer to notify gRPC that some internal
	// state in balancer has changed.
	//
	// gRPC will update the connectivity state of the ClientConn, and will call pick
	// on the new picker to pick new SubConn.
	//
	// Deprecated: use UpdateState instead
	UpdateBalancerState(s connectivity.State, p Picker)

	// 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
}

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 ClientConnState

type ClientConnState struct {
	ResolverState resolver.State
	// The parsed load balancing configuration returned by the builder's
	// ParseConfig method, if implemented.
	BalancerConfig serviceconfig.LoadBalancingConfig
}

ClientConnState describes the state of a ClientConn relevant to the balancer.

type ConfigParser

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)
}

ConfigParser parses load balancer configs.

type ConnectivityStateEvaluator

type ConnectivityStateEvaluator struct {
	// contains filtered or unexported fields
}

ConnectivityStateEvaluator takes the connectivity states of multiple SubConns and returns one aggregated connectivity state.

It's not thread safe.

func (*ConnectivityStateEvaluator) RecordTransition

func (cse *ConnectivityStateEvaluator) RecordTransition(oldState, newState connectivity.State) connectivity.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 the aggregated state is TransientFailure.

Idle and Shutdown are not considered.

type DoneInfo

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{}
}

DoneInfo contains additional information for done.

type NewSubConnOptions

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.
	CredsBundle credentials.Bundle
	// HealthCheckEnabled indicates whether health check service should be
	// enabled on this SubConn
	HealthCheckEnabled bool
}

NewSubConnOptions contains options to create new SubConn.

type PickInfo

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
}

PickInfo contains additional information for the Pick operation.

type PickResult

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)
}

PickResult contains information related to a connection chosen for an RPC.

type Picker

type Picker interface {
	// Pick returns the SubConn to be used to send the RPC.
	// The returned SubConn must be one returned by NewSubConn().
	//
	// This functions is expected to return:
	// - a SubConn that is known to be READY;
	// - ErrNoSubConnAvailable if no SubConn is available, but progress is being
	//   made (for example, some SubConn is in CONNECTING mode);
	// - other errors if no active connecting is happening (for example, all SubConn
	//   are in TRANSIENT_FAILURE mode).
	//
	// If a SubConn is returned:
	// - If it is READY, gRPC will send the RPC on it;
	// - If it is not ready, or becomes not ready after it's returned, gRPC will
	//   block until UpdateBalancerState() is called and will call pick on the
	//   new picker. The done function returned from Pick(), if not nil, will be
	//   called with nil error, no bytes sent and no bytes received.
	//
	// If the returned error is not nil:
	// - If the error is ErrNoSubConnAvailable, gRPC will block until UpdateBalancerState()
	// - If the error is ErrTransientFailure or implements IsTransientFailure()
	//   bool, returning true:
	//   - If the RPC is wait-for-ready, gRPC will block until UpdateBalancerState()
	//     is called to pick again;
	//   - Otherwise, RPC will fail with unavailable error.
	// - Else (error is other non-nil error):
	//   - The RPC will fail with the error's status code, or Unknown if it is
	//     not a status error.
	//
	// The returned done() function will be called once the rpc has finished,
	// with the final status of that RPC.  If the SubConn returned is not a
	// valid SubConn type, done may not be called.  done may be nil if balancer
	// doesn't care about the RPC status.
	Pick(ctx context.Context, info PickInfo) (conn SubConn, done func(DoneInfo), err error)
}

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.UpdateBalancerState().

Deprecated: use V2Picker instead

type State

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 V2Picker
}

State contains the balancer's state relevant to the gRPC ClientConn.

type SubConn

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.
	UpdateAddresses([]resolver.Address)
	// Connect starts the connecting for this SubConn.
	Connect()
}

SubConn represents a gRPC sub connection. Each sub connection contains a list of addresses. gRPC will try to connect to them (in sequence), and stop trying the remainder once one connection is successful.

The reconnect backoff will be applied on the list, not a single address. For example, try_on_all_addresses -> backoff -> try_on_all_addresses.

All SubConns start in IDLE, and will not try to connect. To trigger the connecting, Balancers must call Connect. When the connection encounters an error, it will reconnect immediately. When the connection becomes IDLE, it will not reconnect unless Connect is called.

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 SubConnState

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
}

SubConnState describes the state of a SubConn.

type V2Balancer

type V2Balancer 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()
}

V2Balancer is defined for documentation purposes. If a Balancer also implements V2Balancer, its UpdateClientConnState method will be called instead of HandleResolvedAddrs and its UpdateSubConnState will be called instead of HandleSubConnStateChange.

type V2Picker

type V2Picker 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 implements IsTransientFailure() bool, returning true,
	//   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.
	//
	// - Any other errors terminate all RPCs with the code and message
	//   provided.  If the error is not a status error, it will be converted by
	//   gRPC to a status error with code Unknown.
	Pick(info PickInfo) (PickResult, error)
}

V2Picker 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.UpdateBalancerState().