Epsagon Tracing for Go

This package provides tracing to Go applications for the collection of distributed tracing and performance metrics in Epsagon.

Contents

• Installation
• Usage
  • Tagging Traces
  • Custom Errors
  • Ignored Keys
• Frameworks
• Integrations
• Configuration
• Getting Help
• Opening Issues
• License

Installation

To install Epsagon, simply run:

go get github.com/epsagon/epsagon-go

Or using dep:

dep ensure -add github.com/epsagon/epsagon-go

Usage

Tagging Traces

You can add custom tags to your traces, for easier filtering and aggregations.

Add the following call inside your code:

epsagon.Label("key", "value")
epsagon.Label("user_id", user_id)

You can also use it to ship custom metrics:

epsagon.Label("key", "metric")
epsagon.Label("items_in_cart", items_in_cart)

Valid types are string, bool, int and float. Custom labels are not trimmed with the trace events in case the trace is too big

Custom Errors

You can set a trace as an error (although handled correctly) to get an alert or just follow it on the dashboard. Add the following call inside your code:

epsagon.TypeError("My custom error", "Custom Error Type")
# Or manually add an error
epsagon.TypeError(errors.New("My custom error"), "Custom Error Type")

You can also set a tracer as an error with a default error type:

epsagon.Error("My custom error")
# Or manually add an error
epsagon.Error(errors.New("My custom error"))

Valid types are string and error.

Ignored Keys

You can set keys that will be masked in the sent trace from the events metadata to hide selected information:

	config.IgnoredKeys = []string{"password"}
	client := http.Client{Transport: epsagonhttp.NewTracingTransport(ctx)}
	// This password will be masked in the sent trace:
	decodedJSON, err := json.Marshal(map[string]string{"password": "abcde", "animal": "lion"})
	resp, err := client.Post("http://example.com/upload", "application/json", bytes.NewReader(decodedJSON))

Frameworks

The following frameworks are supported by Epsagon:

AWS Lambda

Tracing Lambda functions can be done in the following method:

package main

import (
	"github.com/aws/aws-lambda-go/events"
	"github.com/aws/aws-lambda-go/lambda"
	"github.com/epsagon/epsagon-go/epsagon"
	"log"
)

func myHandler(request events.APIGatewayProxyRequest) (events.APIGatewayProxyResponse, error) {
	log.Println("In myHandler, received body: ", request.Body)
	return events.APIGatewayProxyResponse{Body: request.Body, StatusCode: 200}, nil
}

func main() {
	log.Println("enter main")
	lambda.Start(epsagon.WrapLambdaHandler(
        epsagon.NewTracerConfig("app-name-stage","epsagon-token"),
        myHandler))
}

Generic

You can instrument a single function, this function can use go routines inside and their operations will still be traced.

func doTask(a int, b string) (int, error) {
	log.Printf("inside doTask: b = %s", b)
	return a + 1, fmt.Errorf("boom")
}
func main() {
	// With Epsagon instrumentation
	config := epsagon.NewTracerConfig("generic-go-wrapper", "")
	config.Debug = true
	response := epsagon.GoWrapper(config, doTask)(5, "hello")
	res2 := response[0].Int()
	errInterface := response[1].Interface()
}

Optionally, you can pass a custom name for your wrapped function. In the epsagon dashboard, your wrapped function will be displayed with your configured name in all the relevant screens: traces search, service map and more.

	response := epsagon.GoWrapper(config, doTask, "<MyInstrumentedFuncName>")(5, "hello")

Concurrent Generic

In order to support more than one function being traced in the same environment (using different goroutines), use this wrapper as shown in the example below. The wrapped function has to receive a context as its first parameter, and pass it to the relevant wrapped operations.

func doTask(ctx context.Context, a int, b string, wg *sync.WaitGroup) (int, error) {
	defer wg.Done()
	log.Printf("inside doTask: b = %s", b)
	client := epsagonhttp.Wrap(http.Client{}, ctx)
	client.Get("https://epsagon.com/")
	return a + 1, fmt.Errorf("boom")
}

func main() {
	config := epsagon.NewTracerConfig("generic-go-wrapper", "")
	config.Debug = true
	var wg sync.WaitGroup
	for i := 0; i < 5; i++ {
		go epsagon.ConcurrentGoWrapper(config, doTask)(i, "hello", &wg)
	}
	wg.Wait()
	time.Sleep(2 * time.Second)
}

Optionally, you can pass a custom name for your wrapped function. In the epsagon dashboard, your wrapped function will be displayed with your configured name in all the relevant screens: traces search, service map and more.

		go epsagon.ConcurrentGoWrapper(config, doTask, "<MyInstrumentedFuncName>")(i, "hello", &wg)

http

Wrapping http handlers with Epsagon:

import (
	"github.com/epsagon/epsagon-go/epsagon"
	epsagonhttp "github.com/epsagon/epsagon-go/wrappers/net/http"
)

func main() {
	mux := http.NewServeMux()
	mux.HandleFunc("/ping", epsagonhttp.WrapHandleFunc(
		epsagon.NewTracerConfig("test-http-mux", ""),
		func(w http.ResponseWriter, req *http.Request) {
			io.WriteString(w, "pong\n")
		}),
        "my-handler-name",
	)

	http.ListenAndServe(":8080", mux)
}

The third and fourth arguments to epsagonhttp.WrapHandleFunc are optional and set the resource name and the hostname. If the resource name is not set then the wrapped funcdtion name is used and the hostname is taken from the request URL if omitted.

	mux.HandleFunc("/ping", epsagonhttp.WrapHandleFunc(
		epsagon.NewTracerConfig("test-http-mux", ""),
		func(w http.ResponseWriter, req *http.Request) {
			io.WriteString(w, "pong\n")
		}),
        "my-handler-name",
		"test.hostname.com",
	)

To wrap nested libraries you can get the epsagon context from the request context:

client := http.Client{
    Transport: epsagonhttp.NewTracingTransport(req.Context())}
resp, err := client.Get("http://example.com")

gin

You can easily instrument gin applications with Epsagon:

import (
	"github.com/epsagon/epsagon-go/epsagon"
	epsagongin "github.com/epsagon/epsagon-go/wrappers/gin"
	"github.com/gin-gonic/gin"
)

func main() {
	r := epsagongin.GinRouterWrapper{
		IRouter:  gin.Default(),
		Hostname: "my_site",
        Config:   epsagon.NewTracerConfig(
        "test-gin-application", "",
        ),
	}

	r.GET("/ping", func(c *gin.Context) {
		c.JSON(200, gin.H{
			"message": "pong",
		})
	})
	r.IRouter.(*gin.Engine).Run()

If you want to instument other integrated libraries inside the gin handler you can get the Epsagon context from the gin.Context to do that:

client := http.Client{
    Transport: epsagonhttp.NewTracingTransport(epsagongin.EpsagonContext(c))}
resp, err := client.Get("http://example.com")

Integrations

Epsagon provides out-of-the-box instrumentation (tracing) for many popular frameworks and libraries.

net/http

Any http request can be traced using a custom RoundTripper implementation and using that in an http.Client:

import (
	"github.com/epsagon/epsagon-go/wrappers/net/http"
...
	client := http.Client{Transport: epsagonhttp.NewTracingTransport()}
	resp, err := client.Get(anyurl)

If you are already using a custom RoundTripper implementation, such as for AWS V4 request signing, you can wrap it:

import (
	"github.com/epsagon/epsagon-go/wrappers/net/http"
...
	rt := &custom.Roundtripper{}
	client := http.Client{Transport: epsagonhttp.NewWrappedTracingTransport(rt)}
	resp, err := client.Get(anyurl)

The wrapped http.Client functionality exists for backwards compatibility:

import (
	"github.com/epsagon/epsagon-go/wrappers/net/http"
...
	client := epsagonhttp.Wrap(http.Client{})
	resp, err := client.Get(anyurl)

If you want to disable data collection only for the calls made by this client set client.MetadataOnly = true

aws-sdk-go

Wrapping of aws-sdk-go is done through the Session object that has to be created to communicate with AWS:

import (
...
	"github.com/epsagon/epsagon-go/wrappers/aws/aws-sdk-go/aws"
)
    ...
	sess := epsagonawswrapper.WrapSession(session.Must(session.NewSession()))
	svcSQS := sqs.New(sess)

aws-sdk-go-v2

Wrapping of aws-sdk-go-v2 is done through the service object:

import (
...
	"github.com/aws/aws-sdk-go-v2/service/dynamodb"
	"github.com/epsagon/epsagon-go/epsagon"
)

	svc := epsagon.WrapAwsV2Service(dynamodb.New(cfg)).(*dynamodb.Client)
    ...

Configuration

Advanced options can be configured as a parameter to the Config struct to the WrapLambdaHandler or as environment variables.

Getting Help

If you have any issue around using the library or the product, please don't hesitate to:

• Use the documentation.
• Use the help widget inside the product.
• Open an issue in GitHub.

Opening Issues

If you encounter a bug with the Epsagon library for Go, we want to hear about it.

When opening a new issue, please provide as much information about the environment:

• Library version, Go runtime version, dependencies, etc.
• Snippet of the usage.
• A reproducible example can really help.

The GitHub issues are intended for bug reports and feature requests. For help and questions about Epsagon, use the help widget inside the product.

License

Provided under the MIT license. See LICENSE for details.

Copyright 2020, Epsagon