package balancer

Import Path
	google.golang.org/grpc/balancer (on go.dev)

Dependency Relation
	imports 14 packages, and imported by 9 packages


Involved Source Files

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

	    conn_state_evaluator.go
	    subconn.go


Package-Level Type Names (total 18, all are exported)


	/* sort exporteds by:  |  */
	
		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.

		
			
				Close closes the balancer. The balancer is not currently required to
				call SubConn.Shutdown for its existing SubConns; however, this will be
				required in a future release, so it is recommended.

			
				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.

			
				ResolverError is called by gRPC when the name resolver reports an error.

			
				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.

			
				UpdateSubConnState is called by gRPC when the state of a SubConn
				changes.
				
				Deprecated: Use NewSubConnOptions.StateListener when creating the
				SubConn instead.

		
			*google.golang.org/grpc/internal/balancer/gracefulswitch.Balancer
			
		
			 Balancer : ExitIdler
			 Balancer : google.golang.org/grpc/balancer/endpointsharding.ExitIdler
		
			func Builder.Build(cc ClientConn, opts BuildOptions) Balancer
			func google.golang.org/grpc/balancer/endpointsharding.NewBalancer(cc ClientConn, opts BuildOptions, childBuilder endpointsharding.ChildBuilderFunc, esOpts endpointsharding.Options) Balancer


	
		Builder creates a balancer.

		
			
				Build creates a new balancer with the ClientConn.

			
				Name returns the name of balancers built by this builder.
				It will be used to pick balancers (for example in service config).

		
			
		
			func Get(name string) Builder
			func google.golang.org/grpc/balancer/base.NewBalancerBuilder(name string, pb base.PickerBuilder, config base.Config) Builder
		
			func Register(b Builder)
			func google.golang.org/grpc/internal/balancer/gracefulswitch.(*Balancer).SwitchTo(builder Builder) error
			


	
		BuildOptions contains additional information for Build.

		
			
				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.

			
				ChannelzParent is the parent ClientConn's channelz channel.

			
				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.

			
				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.

			
				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.

			
				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.

			
				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.

		
			func Builder.Build(cc ClientConn, opts BuildOptions) Balancer
			func google.golang.org/grpc/balancer/endpointsharding.NewBalancer(cc ClientConn, opts BuildOptions, childBuilder endpointsharding.ChildBuilderFunc, esOpts endpointsharding.Options) Balancer
			func google.golang.org/grpc/internal/balancer/gracefulswitch.NewBalancer(cc ClientConn, opts BuildOptions) *gracefulswitch.Balancer


	
		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.
		
		NOTICE: This interface is intended to be implemented by gRPC, or intercepted
		by custom load balancing polices.  Users should not need their own complete
		implementation of this interface -- they should always delegate to a
		ClientConn passed to Builder.Build() by embedding it in their
		implementations. An embedded ClientConn must never be nil, or runtime panics
		will occur.

		
			
				MetricsRecorder provides the metrics recorder that balancers can use to
				record metrics. Balancer implementations which do not register metrics on
				metrics registry and record on them can ignore this method. The returned
				MetricsRecorder is guaranteed to never be nil.

			
				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.
				
				Deprecated: please be aware that in a future version, SubConns will only
				support one address per SubConn.

			
				RemoveSubConn removes the SubConn from ClientConn.
				The SubConn will be shutdown.
				
				Deprecated: use SubConn.Shutdown instead.

			
				ResolveNow is called by balancer to notify gRPC to do a name resolving.

			
				Target returns the dial target for this ClientConn.
				
				Deprecated: Use the Target field in the BuildOptions instead.

			
				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 may trigger a state transition for the SubConn.
				
				Deprecated: this method will be removed.  Create new SubConns for new
				addresses instead.

			
				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.

			
		
			
		
			 ClientConn : google.golang.org/grpc/internal.EnforceClientConnEmbedding
		
			func Builder.Build(cc ClientConn, opts BuildOptions) Balancer
			func google.golang.org/grpc/balancer/endpointsharding.NewBalancer(cc ClientConn, opts BuildOptions, childBuilder endpointsharding.ChildBuilderFunc, esOpts endpointsharding.Options) Balancer
			func google.golang.org/grpc/internal/balancer/gracefulswitch.NewBalancer(cc ClientConn, opts BuildOptions) *gracefulswitch.Balancer


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

		
			
				The parsed load balancing configuration returned by the builder's
				ParseConfig method, if implemented.

			ResolverState resolver.State
		
			func Balancer.UpdateClientConnState(ClientConnState) error
			func google.golang.org/grpc/internal/balancer/gracefulswitch.(*Balancer).UpdateClientConnState(state ClientConnState) error


	
		ConfigParser parses load balancer configs.

		
			
				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.

		
			


	
		ConnectivityStateEvaluator takes the connectivity states of multiple SubConns
		and returns one aggregated connectivity state.
		
		It's not thread safe.

		
			
		
			
				CurrentState returns the current aggregate conn state by evaluating the counters

			
				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 Idle, the aggregated state is Idle;
				  - Else if at least one SubConn is TransientFailure (or there are no SubConns), the aggregated state is Transient Failure.
				
				Shutdown is not considered.



	
		DoneInfo contains additional information for done.

		
			
				BytesReceived indicates if any byte has been received from the server.

			
				BytesSent indicates if any bytes have been sent to the server.

			
				Err is the rpc error the RPC finished with. It could be nil.

			
				ServerLoad is the load received from server. It's usually sent as part of
				trailing metadata.
				
				The only supported type now is *orca_v3.LoadReport.

			
				Trailer contains the metadata from the RPC's trailer, if present.



	
		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.
		
		Deprecated: All balancers must implement this interface. This interface will
		be removed in a future release.

		
			
				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.

		
			 Balancer (interface)
			 google.golang.org/grpc/balancer/endpointsharding.ExitIdler (interface)
			*google.golang.org/grpc/internal/balancer/gracefulswitch.Balancer
			
		
			 ExitIdler : google.golang.org/grpc/balancer/endpointsharding.ExitIdler


	
		NewSubConnOptions contains options to create new SubConn.

		
			
				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.

			
				HealthCheckEnabled indicates whether health check service should be
				enabled on this SubConn

			
				StateListener is called when the state of the subconn changes.  If nil,
				Balancer.UpdateSubConnState will be called instead.  Will never be
				invoked until after Connect() is called on the SubConn created with
				these options.

		
			func ClientConn.NewSubConn([]resolver.Address, NewSubConnOptions) (SubConn, 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.UpdateState().

		
			
				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.

		
			
		
			func google.golang.org/grpc/balancer/base.NewErrPicker(err error) Picker
			func google.golang.org/grpc/balancer/base.PickerBuilder.Build(info base.PickerBuildInfo) Picker
		
			func google.golang.org/grpc/balancer/endpointsharding.ChildStatesFromPicker(picker Picker) []endpointsharding.ChildState


	
		PickInfo contains additional information for the Pick operation.

		
			
				Ctx is the RPC's context, and may contain relevant RPC-level information
				like the outgoing header metadata.

			
				FullMethodName is the method name that NewClientStream() is called
				with. The canonical format is /service/Method.

		
			func Picker.Pick(info PickInfo) (PickResult, error)


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

		
			
				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.

			
				Metadata provides a way for LB policies to inject arbitrary per-call
				metadata. Any metadata returned here will be merged with existing
				metadata added by the client application.
				
				LB policies with child policies are responsible for propagating metadata
				injected by their children to the ClientConn, as part of Pick().

			
				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.

		
			func Picker.Pick(info PickInfo) (PickResult, error)
		
			


	
		A Producer is a type shared among potentially many consumers.  It is
		associated with a SubConn, and an implementation will typically contain
		other methods to provide additional functionality, e.g. configuration or
		subscription registration.

		
			func ProducerBuilder.Build(grpcClientConnInterface any) (p Producer, close func())
			func SubConn.GetOrBuildProducer(ProducerBuilder) (p Producer, close func())


	
		A ProducerBuilder is a simple constructor for a Producer.  It is used by the
		SubConn to create producers when needed.

		
			
				Build creates a Producer.  The first parameter is always a
				grpc.ClientConnInterface (a type to allow creating RPCs/streams on the
				associated SubConn), but is declared as `any` to avoid a dependency
				cycle.  Build also returns a close function that will be called when all
				references to the Producer have been given up for a SubConn, or when a
				connectivity state change occurs on the SubConn.  The close function
				should always block until all asynchronous cleanup work is completed.

		
			
		
			func SubConn.GetOrBuildProducer(ProducerBuilder) (p Producer, close func())


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

		
			
				State contains the connectivity state of the balancer, which is used to
				determine the state of the ClientConn.

			
				Picker is used to choose connections (SubConns) for RPCs.

		
			func ClientConn.UpdateState(State)


	
		A SubConn represents a single connection to a gRPC backend service.
		
		All SubConns start in IDLE, and will not try to connect. To trigger a
		connection attempt, Balancers must call Connect.
		
		If the connection attempt fails, the SubConn will transition to
		TRANSIENT_FAILURE for a backoff period, and then return to IDLE.  If the
		connection attempt succeeds, it will transition to READY.
		
		If a READY SubConn becomes disconnected, the SubConn will transition to IDLE.
		
		If a connection re-enters IDLE, Balancers must call Connect again to trigger
		a new connection attempt.
		
		Each SubConn contains a list of addresses.  gRPC will try to connect to the
		addresses in sequence, and stop trying the remainder once the first
		connection is successful.  However, this behavior is deprecated.  SubConns
		should only use a single address.
		
		NOTICE: This interface is intended to be implemented by gRPC, or intercepted
		by custom load balancing polices.  Users should not need their own complete
		implementation of this interface -- they should always delegate to a SubConn
		returned by ClientConn.NewSubConn() by embedding it in their implementations.
		An embedded SubConn must never be nil, or runtime panics will occur.

		
			
				Connect starts the connecting for this SubConn.

			
				GetOrBuildProducer returns a reference to the existing Producer for this
				ProducerBuilder in this SubConn, or, if one does not currently exist,
				creates a new one and returns it.  Returns a close function which may be
				called when the Producer is no longer needed.  Otherwise the producer
				will automatically be closed upon connection loss or subchannel close.
				Should only be called on a SubConn in state Ready.  Otherwise the
				producer will be unable to create streams.

			
				RegisterHealthListener registers a health listener that receives health
				updates for a Ready SubConn. Only one health listener can be registered
				at a time. A health listener should be registered each time the SubConn's
				connectivity state changes to READY. Registering a health listener when
				the connectivity state is not READY may result in undefined behaviour.
				This method must not be called synchronously while handling an update
				from a previously registered health listener.

			
				Shutdown shuts down the SubConn gracefully.  Any started RPCs will be
				allowed to complete.  No future calls should be made on the SubConn.
				One final state update will be delivered to the StateListener (or
				UpdateSubConnState; deprecated) with ConnectivityState of Shutdown to
				indicate the shutdown operation.  This may be delivered before
				in-progress RPCs are complete and the actual connection is closed.

			
				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 close, and
				a new connection will be created.
				
				This will trigger a state transition for the SubConn.
				
				Deprecated: this method will be removed.  Create new SubConns for new
				addresses instead.

			
		
			
		
			 SubConn : google.golang.org/grpc/internal.EnforceSubConnEmbedding
		
			func ClientConn.NewSubConn([]resolver.Address, NewSubConnOptions) (SubConn, error)
		
			func Balancer.UpdateSubConnState(SubConn, SubConnState)
			func ClientConn.RemoveSubConn(SubConn)
			func ClientConn.UpdateAddresses(SubConn, []resolver.Address)
			func google.golang.org/grpc/internal/balancer/gracefulswitch.(*Balancer).UpdateSubConnState(sc SubConn, state SubConnState)
			


	
		SubConnState describes the state of a SubConn.

		
			
				ConnectionError is set if the ConnectivityState is TransientFailure,
				describing the reason the SubConn failed.  Otherwise, it is nil.

			
				ConnectivityState is the connectivity state of the SubConn.

			
		
			func Balancer.UpdateSubConnState(SubConn, SubConnState)
			func google.golang.org/grpc/internal/balancer/gracefulswitch.(*Balancer).UpdateSubConnState(sc SubConn, state SubConnState)
			




Package-Level Functions (total 7, in which 3 are exported)


	
		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.


	
		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.


	
		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.


	


Package-Level Variables (total 5, in which 3 are exported)


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


	
		ErrNoSubConnAvailable indicates no SubConn is available for pick().
		gRPC will block the RPC until a new picker is available via UpdateState().


	
		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.