Gizmo Microservice Toolkit

This toolkit provides packages to put together server and pubsub daemons with the following features:

• standardized configuration and logging
• health check endpoints with configurable strategies
• configuration for managing pprof endpoints and log levels
• structured logging containing basic request information
• useful metrics for endpoints
• graceful shutdowns
• basic interfaces to define our expectations and vocabulary

In this toolkit, you will find:

The config package

This package contains a handful of structs meant for managing common configuration options and credentials. There are currently configs for:

• MySQL
• MongoDB
• Oracle
• AWS (SNS, SQS, S3)
• Kafka
• Gorilla's securecookie
• Gizmo Servers

The package also has a generic Config type that contains all of the above types. It's meant to be a 'catch all' struct that most applications should be able to use.

config also contains functions to load these config structs from JSON files, JSON blobs in Consul k/v or environment variables.

The server package

This package is the bulk of the toolkit and relies on config for any managing Server implementations. A server must implement the following interface:

// Server is the basic interface that defines what expect from any server.
type Server interface {
    Register(Service) error
    Start() error
    Stop() error
}

The package offers 2 server implementations:

SimpleServer, which is capable of handling basic HTTP and JSON requests via 3 of the available Service implementations: SimpleService, JSONService, and MixedService. A service and these implementations will be defined below.

RPCServer, which is capable of serving a gRPC server on one port and JSON endpoints on another. This kind of server can only handle the RPCService implementation.

The Service interface is minimal to allow for maximum flexibility:

type Service interface {
    Prefix() string

    // Middleware provides a hook for service-wide middleware.
    Middleware(http.Handler) http.Handler
}

The 3 service types that are accepted and hostable on the SimpleServer:

type SimpleService interface {
    Service

    // router - method - func
    Endpoints() map[string]map[string]http.HandlerFunc
}

type JSONService interface {
    Service

    // router - method - func
    JSONEndpoints() map[string]map[string]JSONEndpoint
    // JSONMiddleware provides a hook for service-wide middleware around JSONEndpoints.
    JSONMiddleware(JSONEndpoint) JSONEndpoint
}

type MixedService interface {
    Service

    // route - method - func
    Endpoints() map[string]map[string]http.HandlerFunc

    // route - method - func
    JSONEndpoints() map[string]map[string]JSONEndpoint
    // JSONMiddleware provides a hook for service-wide middleware around JSONEndpoints.
    JSONMiddleware(JSONEndpoint) JSONEndpoint
}

Where a JSONEndpoint is defined as:

type JSONEndpoint func(*http.Request) (int, interface{}, error)

Also, the one service type that works with an RPCServer:

type RPCService interface {
    Service

    Service() (grpc.ServiceDesc, interface{})

    // route - method - func
    JSONEndpoints() map[string]map[string]JSONEndpoint
    // JSONMiddleware provides a hook for service-wide middleware around JSONEndpoints.
    JSONMiddlware(JSONEndpoint) JSONEndpoint
}

The Middleware(..) functions offer each service a 'hook' to wrap each of it's endpoints. This may be handy for adding additional headers or context to the request. This is also the point where other, third-party middleware could be easily be plugged in (i.e. oauth, tracing, metrics, logging, etc.)

The pubsub package

This package contains two generic interfaces for publishing data to queues and subscribing and consuming data from those queues.

// Publisher is a generic interface to encapsulate how we want our publishers
// to behave. Until we find reason to change, we're forcing all publishers
// to emit protobufs.
type Publisher interface {
    // Publish will publish a message.
    Publish(string, proto.Message) error
    // Publish will publish a []byte message.
    PublishRaw(string, []byte) error
}

// Subscriber is a generic interface to encapsulate how we want our subscribers
// to behave. For now the system will auto stop if it encounters any errors. If
// a user encounters a closed channel, they should check the Err() method to see
// what happened.
type Subscriber interface {
    // Start will return a channel of raw messages.
    Start() <-chan SubscriberMessage
    // Err will contain any errors returned from the consumer connection.
    Err() error
    // Stop will initiate a graceful shutdown of the subscriber connection.
    Stop() error
}

Where a SubscriberMessage is an interface that gives implementations a hook for acknowledging/delete messages. Take a look at the docs for each implementation in pubsub to see how they behave.

There are currently 2 implementations of each type of pubsub interfaces:

For pubsub via Amazon's SNS/SQS, you can use the SNSPublisher and the SQSSubscriber.

For pubsub via Kafka topics, you can use the KakfaPublisher and the KafkaSubscriber.

The pubsub/pubsubtest package

This package contains 'test' implementations of the pubsub.Publisher and pubsub.Subscriber interfaces that will allow developers to easily mock out and test their pubsub implementations:

type TestPublisher struct {
    // Published will contain a list of all messages that have been published.
    Published []TestPublishMsg

    // GivenError will be returned by the TestPublisher on publish.
    // Good for testing error scenarios.
    GivenError error

    // FoundError will contain any errors encountered while marshalling
    // the protobuf struct.
    FoundError error
}

type TestSubscriber struct {
    // ProtoMessages will be marshalled into []byte  used to mock out
    // a feed if it is populated.
    ProtoMessages []proto.Message

    // JSONMEssages will be marshalled into []byte and used to mock out
    // a feed if it is populated.
    JSONMessages []interface{}

    // GivenErrError will be returned by the TestSubscriber on Err().
    // Good for testing error scenarios.
    GivenErrError error

    // GivenStopError will be returned by the TestSubscriber on Stop().
    // Good for testing error scenarios.
    GivenStopError error

    // FoundError will contain any errors encountered while marshalling
    // the JSON and protobuf struct.
    FoundError error
}

The web package

This package contains a handful of very useful functions for parsing types from request queries and payloads.

Examples

• Several reference implementations utilizing server and pubsub are available in the 'examples' subdirectory.

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