sleuth
is a Go library that provides master-less peer-to-peer autodiscovery and RPC
between HTTP services that reside on the same network. It works with minimal
configuration and provides a mechanism to join a local network both as a
client that offers no services and as any service that speaks HTTP. Its
primary use case is for microservices on the same network that make calls to
one another.
For a full introduction and tutorial, check out: Service autodiscovery in Go with sleuth
sleuth
is dependent on libzmq
, which can be installed either from source or from binaries. For more information, please refer to ØMQ: "Get the Software" or the libzmq
repository.
Another option is to use a Docker container that comes with Go and ZeroMQ.
Once libzmq
is available on a system, sleuth
can be installed like any other Go library:
go get -u github.com/ursiform/sleuth
Example (1): The echo-service
is a toy service that merely echoes back anything in an HTTP request body. It has made itself available on a sleuth
network:
package main
import (
"io/ioutil"
"net/http"
"github.com/ursiform/sleuth"
)
type echoHandler struct{}
func (h *echoHandler) ServeHTTP(res http.ResponseWriter, req *http.Request) {
body, _ := ioutil.ReadAll(req.Body)
res.Write(body)
}
func main() {
handler := new(echoHandler)
// In the real world, the Interface field of the sleuth.Config object
// should be set so that all services are on the same subnet.
config := &sleuth.Config{Handler: handler, Service: "echo-service"}
server, err := sleuth.New(config)
if err != nil {
panic(err.Error())
}
defer server.Close()
http.ListenAndServe(":9873", handler)
}
And here is a trivial client that waits until it has connected to the network and found the echo-service
to make a request before it exits. Note that the *sleuth.Client
works as a drop-in replacement for an *http.Client
when making requests using the Do
method:
package main
import (
"bytes"
"fmt"
"io/ioutil"
"net/http"
"github.com/ursiform/sleuth"
)
func main() {
service := "echo-service"
// In the real world, the Interface field of the sleuth.Config object
// should be set so that all services are on the same subnet.
config := &sleuth.Config{LogLevel: "silent"}
client, err := sleuth.New(config)
if err != nil {
panic(err.Error())
}
defer client.Close()
client.WaitFor(service)
input := "This is the value I am inputting."
body := bytes.NewBuffer([]byte(input))
request, _ := http.NewRequest("POST", "sleuth://"+service+"/", body)
response, err := client.Do(request)
if err != nil {
panic(err.Error())
}
output, _ := ioutil.ReadAll(response.Body)
if string(output) == input {
fmt.Println("It works.")
} else {
fmt.Println("It doesn't work.")
}
}
Example (2): sleuth-example
is a fuller example of two services on a sleuth
network that need to communicate with each other.
A complete tutorial based on that example can be found here: Service autodiscovery in Go with sleuth.
go test -cover github.com/ursiform/sleuth
Q: What is the messaging protocol sleuth
uses?
A: Under the hood, sleuth
marshals HTTP requests and responses into plain JSON objects and then compresses them via gzip
. Instead of adding another dependency on something like Protocol Buffers, sleuth
depends on the fact that most API responses between microservices will be fairly small and it leaves the door open to ports in a wide variety of languages and environments. One hard dependency seemed quite enough.
Q: What if I have multiple instances of the same service?
A: Great! sleuth
will automatically round-robin the requests each client makes to all services that share the same name.
Q: What happens if a service goes offline?
A: Whenever possible, a service should call its client's Close()
method before exiting to notify the network of its departure. But even if a service fails to do that, the sleuth
network's underlying Gyre
network will detect within about one second that a peer has disappeared. All requests to that service will be routed to other peers offering the same service. If no peers exist for that service, then calls to Do()
will return an unknown service error (code 919
), which means that if you're already handling errors when making requests, you're covered.
Q: It doesn't work.
A: That's not a question. But have you checked to make sure your firewall allows UDP
traffic on port 5670
?
Q: It still doesn't work.
A: That's still not a question. But have you set the Interface
field of your sleuth.Config
object? The services you want to connect need to be on the same network and if you leave that field blank, the underlying Gyre
network may not reside where you think it does. If you run ifconfig
you'll get a list of available interfaces on your system.
Q: Why is it called sleuth
?
A: Because "sleuth" is the collective noun for a group of bears: the original reason for writing this library was to connect a group of bear/forest services. Also because a sleuth searches for things and discovers them. Hence the logo:
sleuth
is licensed under the MIT License.
The underlying libraries that sleuth
relies on, Gyre
and libzmq
, are licensed under the LGPL. In effect, users who do not plan on modifying Gyre
or libzmq
can release their own applications under any license they see fit.