itopo

Documentation

Overview

Package itopo stores topology state and manages topology updates for an application.

The package must be initialized with Init. In subsequent updates through Update, the new topology is checked whether it is compatible with the previous version. The rules differ between services.

Updates

The update of the topology is only valid if a set of constraints is met. The constraints differ between the initialized service types.

In a topology update, when the diff is empty, the topology is only updated if it expires later than the current topology. Otherwise, Update succeeds and indicates that the in-memory copy has not been updated.

The client package can register callbacks to be notified about certain events.

Index

• func Get() topology.Topology
• func Init(cfg *Config)
• func Provider() topology.Provider
• func TopologyHandler(w http.ResponseWriter, r *http.Request)
• func Update(static topology.Topology) error
• type Callbacks
• type Config
• type Transaction
  • func BeginUpdate(static *topology.RWTopology) (Transaction, error)
  • func (tx *Transaction) Commit() error
  • func (tx *Transaction) Get() topology.Topology
  • func (tx *Transaction) IsUpdate() bool

Functions

func Get

func Get() topology.Topology

Get atomically gets the pointer to the current topology.

func Init

func Init(cfg *Config)

Init initializes the itopo package. A topology must be initialized by calling Update.

func Provider

func Provider() topology.Provider

Provider returns a topology provider that calls Get internally.

func TopologyHandler

func TopologyHandler(w http.ResponseWriter, r *http.Request)

func Update

func Update(static topology.Topology) error

Update atomically sets the topology.

Types

type Callbacks

type Callbacks struct {
	// OnUpdate is called whenever the pointer to static topology is updated.
	OnUpdate func()
}

Callbacks are callbacks to respond to specific topology update events.

type Config

type Config struct {
	// ID is the application identifier.
	ID string
	// Svc is the service type of the application. Updated are treated differently depending
	// on it.
	Svc topology.ServiceType
	// Callbacks can be used to run custom code on specific events.
	Callbacks Callbacks
	// TopologyFactory is used to build Topology facades for the underlying topology object.
	// If nil, topology.FromRWTopology is used.
	TopologyFactory func(*topology.RWTopology) topology.Topology
}

Config is used to initialize the package.

type Transaction

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

Transaction allows to get a view on which topology will be active without committing to the topology update yet.

func BeginUpdate

func BeginUpdate(static *topology.RWTopology) (Transaction, error)

BeginUpdate checks whether setting the static topology is permissible. The returned transaction provides a view on which topology would be active, if committed.

func (*Transaction) Commit

func (tx *Transaction) Commit() error

Commit commits the change. An error is returned, if the static topology changed in the meantime.

func (*Transaction) Get

func (tx *Transaction) Get() topology.Topology

Get returns the topology that will be active if the transaction is committed.

func (*Transaction) IsUpdate

func (tx *Transaction) IsUpdate() bool

IsUpdate indicates whether the transaction will cause an update.