Endure

Endure is an open-source (MIT licensed) plugin container with IoC and self-healing.

Features

• Supports structs and interfaces (see examples)
• Use graph to topologically sort, run, stop and restart dependent plugins
• Algorithms used: graph and double-linked list
• Support easy to add Middleware plugins
• Error reporting
• Automatically restart failing vertices

Installation

go get -u github.com/roadrunner-server/endure

Why?

Imagine you have an application in which you want to implement plugin system. These plugins can depend on each other ( via interfaces or directly). For example, we have 3 plugins: HTTP (to communicate with world), DB (to save the world) and logger (to see the progress).
In this particular case, we can't start HTTP before we start all other parts. Also, we have to initialize logger first, because all parts of our system need logger. All you need to do in Endure is to pass HTTP, DB and Logger structs to the Endure and implement Endure interface. So, the dependency graph will be the following:

First step is to initialize the endure container:

container, err := endure.NewContainer(nil, endure.SetLogLevel(endure.ErrorLevel), endure.Visualize(endure.StdOut, ""))

Let's take a look at the endure.NewContainer():

1. First arg here is the external logger. If you want to use your own logger, you can pass it as the first argument.
2. Next arguments are optional and can be set using Options. For example endure.Visualize(endure.StdOut, "") will show you dot-compatible graph in the console. Then we need to pass our structures as references to the RegisterAll or Register function.

err = container.RegisterAll(
    &httpPlugin{},
    &DBPlugin{},
    &LoggerPlugin{})
    if err != nil {
        panic(err)
}

The order of plugins in the RegisterAll plugin does no matter.
Next we need to initialize and run our container:

err := container.Init()
    if err != nil {
        panic(err)
}
errCh, err := container.Serve()
    if err != nil {
    	panic(err)
}

errCh is the channel with errors from the all Vertices. You can identify vertex by vertexID which is presented in errCh struct. Then just process the events from the errCh:

for {
    select {
        case e := <-errCh:
            println(e.Error.Err.Error()) // just print the error, but actually error processing could be there
            er := container.Stop()
            if er != nil {
                panic(er)
            }
        return
    }
}

Also Endure will take care of the restart failing vertices (HTTP, DB, Logger in example) with exponential backoff mechanism.
The start will proceed in topological order (Logger -> DB -> HTTP), and the stop in reverse-topological order automatically.

Endure main interface

package sample

type (
	// This is the main Endure service interface which may be implemented to Start (Serve) and Stop plugin (OPTIONAL)
	Service interface {
		// Serve
		Serve() chan error
		// Stop
		Stop() error
	}

	// Name of the service (OPTIONAL)
	Named interface {
		Name() string
	}

	// Provider declares the ability to provide dependencies to other plugins (OPTIONAL)
	Provider interface {
		Provides() []interface{}
	}

	// Collector declares the ability to accept the plugins which match the provided method signature (OPTIONAL)
	Collector interface {
		Collects() []interface{}
	}
)

// Init is mandatory to implement
type Plugin struct{}

func (p *Plugin) Init( /* deps here */) error {
	return nil
}

Order is the following:

1. Init() error - is mandatory to implement. For your structure (which you pass to Endure), you should have this method as the method of the struct(go func (p *Plugin) Init() error {}). It can accept as a parameter any passed to the Endure structure (see samples) or interface (with limitations).
2. Service - is optional to implement. It has 2 methods - Serve which should run the plugin and return initialized golang channel with errors, and Stop to shut down the plugin. The Stop and Serve should not block the execution.
3. Provider - is optional to implement. It is used to provide some dependency if you need to extend your struct without deep modification.
4. Collector - is optional to implement. It is used to mark a structure (vertex) as some struct dependency. It can accept interfaces which implement a caller.
5. Named - is mandatory to implement. This is a special kind of interface which provides the name of the struct ( plugin, vertex) to the caller. Is useful in logger (for example) to know user-friendly plugin name.

Available options:

1. SetLogLevel - used to set internal log level. Available options: endure.DebugLevel, endure.InfoLevel,endure.WarnLevel,endure.ErrorLevel,endure.DPanicLevel,endure.PanicLevel,endure.FatalLevel ordered from the most to the least verbosity level.
2. RetryOnFail: bool, used to reinitialize graph w/o stopping application when error received from the Serve.
3. SetBackoff: initialInterval, maxInterval, time.Duration. When RetryOnFail is set, backoff configures how much time spend to reinitialize vertex.
4. Visualize: Output (endure.StdOut, endure.File), path. Graph visualization option via the graphviz. The Graphviz diagram can be shown via stdout or file (path should not be empty).
5. GracefulShutdownTimeout: time.Duration. How long to wait for a vertex (plugin) to stop.

The fully operational example located in the examples folder.

Known issues:

• Vertex can provide only 1 implementaion per interface. For example, at the moment, you can't provide two implementations of the Logger interface within the same vertex.
• No support for the type aliases.