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New Relic Go Agent Guide

Upgrading

This guide documents version 3.x of the agent which resides in package "github.com/newrelic/go-agent/v3/newrelic". If you have already been using version 2.X of the agent and are upgrading to version 3.0, see our Migration Guide for details.

Installation

(Also see GETTING_STARTED if you are using the Go agent for the first time).

In order to install the New Relic Go agent, you need a New Relic license key. Then, installing the Go Agent is the same as installing any other Go library. The simplest way is to run:

go get github.com/newrelic/go-agent/v3/newrelic

Then import the package in your application:

import "github.com/newrelic/go-agent/v3/newrelic"

Initialize the New Relic Go agent by adding the following Config options and Application settings in the main function or in an init block:

app, err := newrelic.NewApplication(
    newrelic.ConfigAppName("Your Application Name"),
    newrelic.ConfigLicense("__YOUR_NEW_RELIC_LICENSE_KEY__"),
)

This will allow you to see Go runtime information.

Now, add instrumentation to your Go application to get additional performance data:

Compile and deploy your application.

Find your application in the New Relic UI. Click on it to see application performance, including the Go runtime page that shows information about goroutine counts, garbage collection, memory, and CPU usage. Data should show up within 5 minutes.

If you are working in a development environment or running unit tests, you may not want the Go Agent to spawn goroutines or report to New Relic. You're in luck! Use the ConfigEnabled function to disable the agent. This makes the license key optional.

app, err := newrelic.NewApplication(
    newrelic.ConfigAppName("Your Application Name"),
    newrelic.ConfigEnabled(false),
)

Full list of Config options and Application settings

Logging

The agent's logging system is designed to be easily extensible. By default, no logging will occur. To enable logging, use the following config functions with an io.Writer: ConfigInfoLogger, which logs at info level, and ConfigDebugLogger which logs at debug level.

To log at debug level to standard out, set:

app, err := newrelic.NewApplication(
    newrelic.ConfigAppName("Your Application Name"),
    newrelic.ConfigLicense("__YOUR_NEW_RELIC_LICENSE_KEY__"),
    // Add debug logging:
    newrelic.ConfigDebugLogger(os.Stdout),
)

To log at info level to a file, set:

w, err := os.OpenFile("my_log_file", os.O_CREATE|os.O_APPEND|os.O_WRONLY, 0644)
if nil == err {
    app, _ := newrelic.NewApplication(
        newrelic.ConfigAppName("Your Application Name"),
        newrelic.ConfigLicense("__YOUR_NEW_RELIC_LICENSE_KEY__"),
        newrelic.ConfigInfoLogger(w),
    )
}

Popular logging libraries logrus, logxi and zap are supported by integration packages:

Transactions

Transactions time requests and background tasks. The simplest way to create transactions is to use Application.StartTransaction and Transaction.End.

txn := app.StartTransaction("transactionName")
defer txn.End()

If you are instrumenting a background transaction, this is all that is needed. If, however, you are instrumenting a web transaction, you will want to use the SetWebRequestHTTP and SetWebResponse methods as well.

SetWebRequestHTTP marks the transaction as a web transaction. If the http.Request is non-nil, SetWebRequestHTTP will additionally collect details on request attributes, url, and method. If headers are present, the agent will look for a distributed tracing header.

If you want to mark a transaction as a web transaction, but don't have access to an http.Request, you can use the SetWebRequest method, using a manually constructed WebRequest object.

SetWebResponse allows the Transaction to instrument response code and response headers. Pass in your http.ResponseWriter as a parameter, and then use the return value of this method in place of the input parameter in your instrumentation.

Here is an example using both methods:

func (h *handler) ServeHTTP(writer http.ResponseWriter, req *http.Request) {
    txn := h.App.StartTransaction("transactionName")
    defer txn.End()
    // This marks the transaction as a web transactions and collects details on
    // the request attributes
    txn.SetWebRequestHTTP(req)
    // This collects details on response code and headers. Use the returned
    // Writer from here on.
    writer = txn.SetWebResponse(writer)
    // ... handler code continues here using the new writer
}

The transaction has helpful methods like NoticeError and SetName. See more in godocs.

If you are using http.ServeMux, use WrapHandle and WrapHandleFunc. These wrappers automatically start and end transactions with the request and response writer.

http.HandleFunc(newrelic.WrapHandleFunc(app, "/users", usersHandler))

To access the transaction in your handler, we recommend getting it from the Request context:

func myHandler(w http.ResponseWriter, r *http.Request) {
    txn := newrelic.FromContext(r.Context())
    // ... handler code here
}

To monitor a transaction across multiple goroutines, use Transaction.NewGoroutine(). The NewGoroutine method returns a new reference to the Transaction, which is required by each segment-creating goroutine. It does not matter if you call NewGoroutine before or after the other goroutine starts.

go func(txn newrelic.Transaction) {
	defer txn.StartSegment("async").End()
	time.Sleep(100 * time.Millisecond)
}(txn.NewGoroutine())

Segments

Find out where the time in your transactions is being spent!

Segment is used to instrument functions, methods, and blocks of code. A segment begins when its StartTime field is populated, and finishes when its End method is called.

segment := newrelic.Segment{}
segment.Name = "mySegmentName"
segment.StartTime = txn.StartSegmentNow()
// ... code you want to time here ...
segment.End()

Transaction.StartSegment is a convenient helper. It creates a segment and starts it:

segment := txn.StartSegment("mySegmentName")
// ... code you want to time here ...
segment.End()

Timing a function is easy using StartSegment and defer. Just add the following line to the beginning of that function:

defer txn.StartSegment("mySegmentName").End()

Segments may be nested. The segment being ended must be the most recently started segment.

s1 := txn.StartSegment("outerSegment")
s2 := txn.StartSegment("innerSegment")
// s2 must be ended before s1
s2.End()
s1.End()

A zero value segment may safely be ended. Therefore, the following code is safe even if the conditional fails:

var s newrelic.Segment
txn := newrelic.FromContext(ctx)
if shouldDoSomething() {
    s.StartTime = txn.StartSegmentNow(),
}
// ... code you wish to time here ...
s.End()

Datastore Segments

Datastore segments appear in the transaction "Breakdown table" and in the "Databases" page.

Datastore segments are instrumented using DatastoreSegment. Just like basic segments, datastore segments begin when the StartTime field is populated and finish when the End method is called. Here is an example:

s := newrelic.DatastoreSegment{
    // Product is the datastore type.  See the constants in
    // https://github.com/newrelic/go-agent/blob/master/v3/newrelic/datastore.go.  Product
    // is one of the fields primarily responsible for the grouping of Datastore
    // metrics.
    Product: newrelic.DatastoreMySQL,
    // Collection is the table or group being operated upon in the datastore,
    // e.g. "users_table".  This becomes the db.collection attribute on Span
    // events and Transaction Trace segments.  Collection is one of the fields
    // primarily responsible for the grouping of Datastore metrics.
    Collection: "users_table",
    // Operation is the relevant action, e.g. "SELECT" or "GET".  Operation is
    // one of the fields primarily responsible for the grouping of Datastore
    // metrics.
    Operation: "SELECT",
}
s.StartTime = txn.StartSegmentNow()
// ... make the datastore call
s.End()

This may be combined into two lines when instrumenting a datastore call that spans an entire function call:

s := newrelic.DatastoreSegment{
    StartTime:  txn.StartSegmentNow(),
    Product:    newrelic.DatastoreMySQL,
    Collection: "my_table",
    Operation:  "SELECT",
}
defer s.End()

If you are using the standard library's database/sql package with MySQL, PostgreSQL, or SQLite then you can avoid creating DatastoreSegments by hand by using an integration package:

External Segments

External segments appear in the transaction "Breakdown table" and in the "External services" page. Version 1.11.0 of the Go Agent adds support for cross-application tracing (CAT), which will result in external segments also appearing in the "Service maps" page and being linked in transaction traces when both sides of the request have traces. Version 2.1.0 of the Go Agent adds support for distributed tracing, which lets you see the path a request takes as it travels through distributed APM apps.

External segments are instrumented using ExternalSegment. There are three ways to use this functionality:

  1. Using StartExternalSegment to create an ExternalSegment before the request is sent, and then calling ExternalSegment.End when the external request is complete.

    For CAT support to operate, an http.Request must be provided to StartExternalSegment, and the ExternalSegment.Response field must be set before ExternalSegment.End is called or deferred.

    For example:

    func external(txn *newrelic.Transaction, req *http.Request) (*http.Response, error) {
  s := newrelic.StartExternalSegment(txn, req)
  response, err := http.DefaultClient.Do(req)
  s.Response = response
  s.End()
  return response, err
}

    If the transaction is nil then StartExternalSegment will look for a transaction in the request's context using FromContext.

  2. Using NewRoundTripper to get a http.RoundTripper that will automatically instrument all requests made via http.Client instances that use that round tripper as their Transport. This option results in CAT support, provided the Go Agent is version 1.11.0, and in distributed tracing support, provided the Go Agent is version 2.1.0. NewRoundTripper will look for a transaction in the request's context using FromContext.

    For example:

    client := &http.Client{}
client.Transport = newrelic.NewRoundTripper(client.Transport)
request, _ := http.NewRequest("GET", "http://example.com", nil)
// Put transaction in the request's context:
request = newrelic.RequestWithTransactionContext(request, txn)
resp, err := client.Do(request)

  3. Directly creating an ExternalSegment via a struct literal with an explicit URL or Request, and then calling ExternalSegment.End. This option does not support CAT, and may be removed or changed in a future major version of the Go Agent. As a result, we suggest using one of the other options above wherever possible.

    For example:

    func external(txn newrelic.Transaction, url string) (*http.Response, error) {
  es := newrelic.ExternalSegment{
    StartTime: txn.StartSegmentNow(),
    URL:   url,
  }
  defer es.End()

  return http.Get(url)
}

Message Producer Segments

Message producer segments appear in the transaction "Breakdown table".

Message producer segments are instrumented using MessageProducerSegment. Just like basic segments, message producer segments begin when the StartTime field is populated and finish when the End method is called. Here is an example:

s := newrelic.MessageProducerSegment{
    // Library is the name of the library instrumented.
    Library: "RabbitMQ",
    // DestinationType is the destination type.
    DestinationType: newrelic.MessageExchange,
    // DestinationName is the name of your queue or topic.
    DestinationName: "myExchange",
    // DestinationTemporary must be set to true if destination is temporary
    // to improve metric grouping.
    DestinationTemporary: false,
}
s.StartTime = txn.StartSegmentNow()
// ... add message to queue here
s.End()

This may be combined into two lines when instrumenting a message producer call that spans an entire function call:

s := newrelic.MessageProducerSegment{
    StartTime:            txn.StartSegmentNow(),
    Library:              "RabbitMQ",
    DestinationType:      newrelic.MessageExchange,
    DestinationName:      "myExchange",
    DestinationTemporary: false,
}
defer s.End()

Attributes

Attributes add context to errors and allow you to filter performance data in Insights.

You may add them using the Transaction.AddAttribute and Segment.AddAttribute methods.

txn.AddAttribute("key", "value")
txn.AddAttribute("product", "widget")
txn.AddAttribute("price", 19.99)
txn.AddAttribute("importantCustomer", true)

seg.AddAttribute("count", 14)

Some attributes are recorded automatically. These are called agent attributes. They are listed here:

To disable one of these agents attributes, for example AttributeHostDisplayName, modify the config like this:

app, err := newrelic.NewApplication(
    newrelic.ConfigAppName("Your Application Name"),    
    newrelic.ConfigLicense("__YOUR_NEW_RELIC_LICENSE_KEY__"),
    func(cfg *newrelic.Config) {
        config.Attributes.Exclude = append(config.Attributes.Exclude, newrelic.AttributeHostDisplayName)
    }
)

Tracing

New Relic's distributed tracing is the next generation of the previous cross-application tracing feature. Compared to cross-application tracing, distributed tracing gives more detail about cross-service activity and provides more complete end-to-end visibility. This section discusses distributed tracing and cross-application tracing in turn.

Distributed Tracing

New Relic's distributed tracing feature lets you see the path that a request takes as it travels through distributed APM apps, which is vital for applications implementing a service-oriented or microservices architecture. Support for distributed tracing was added in version 2.1.0 of the Go Agent.

The config's DistributedTracer.Enabled field has to be set. When true, the agent will add distributed tracing headers in outbound requests, and scan incoming requests for distributed tracing headers. Distributed tracing will override cross-application tracing.

app, err := newrelic.NewApplication(
    newrelic.ConfigAppName("Your Application Name"),
    newrelic.ConfigLicense("__YOUR_NEW_RELIC_LICENSE_KEY__"),
    newrelic.ConfigDistributedTracerEnabled(true),  
)

Cross-Application Tracing [Deprecated]

New Relic's cross-application tracing feature, or CAT for short, links transactions between applications in APM to help identify performance problems within your service-oriented architecture. Support for CAT was added in version 1.11.0 of the Go Agent. We recommend using Distributed Tracing as the most recent, complete feature.

As CAT uses HTTP headers to track requests across applications, the Go Agent needs to be able to access and modify request and response headers both for incoming and outgoing requests.

Tracing Instrumentation

Both distributed tracing and cross-application tracing work by propagating header information from service to service in a request path. In many scenarios, the Go Agent offers tracing instrumentation out-of-the-box, for both distributed tracing and cross-application tracing. For other scenarios customers may implement distributed tracing based on the examples provided in this guide.

Getting Tracing Instrumentation Out-of-the-Box

The Go Agent automatically creates and propagates tracing header information for each of the following scenarios:

For server applications:

  1. Using WrapHandle or WrapHandleFunc to instrument a server that uses http.ServeMux (Example).

  2. Using any of the Go Agent's HTTP integrations, which are listed here .

  3. Using another framework or http.Server while ensuring that:

    1. After calling StartTransaction, make sure to call Transaction.SetWebRequest and Transaction.SetWebResponse on the transaction, and
    2. the http.ResponseWriter that is returned from Transaction.SetWebResponse is used instead of calling WriteHeader directly on the original response writer, as described in the transactions section of this guide (Example).

For client applications:

  1. Using NewRoundTripper, as described in the external segments section of this guide (Example).

  2. Using the call StartExternalSegment and providing an http.Request, as described in the external segments section of this guide (Example).

Manually Implementing Distributed Tracing

Consider manual instrumentation for services not instrumented automatically by the Go Agent. In such scenarios, the calling service has to insert the appropriate header(s) into the request headers:

var h http.Headers
callingTxn.InsertDistributedTraceHeaders(h)

These headers have to be added to the call to the destination service, which in turn invokes the call for accepting the headers:

var h http.Headers
calledTxn.AcceptDistributedTraceHeaders(newrelic.TransportOther, h)

A complete example can be found here.

Custom Metrics

You may create custom metrics via the RecordCustomMetric method.

app.RecordCustomMetric(
    "CustomMetricName", // Name of your metric
    132,                // Value
)

Note: The Go Agent will automatically prepend the metric name you pass to RecordCustomMetric ("CustomMetricName" above) with the string Custom/. This means the above code would produce a metric named Custom/CustomMetricName. You'll also want to read over the Naming Transactions and Metrics section below for advice on coming up with appropriate metric names.

Custom Events

You may track arbitrary events using custom Insights events.

app.RecordCustomEvent("MyEventType", map[string]interface{}{
    "myString": "hello",
    "myFloat":  0.603,
    "myInt":    123,
    "myBool":   true,
})

Request Queuing

If you are running a load balancer or reverse web proxy then you may configure it to add a X-Queue-Start header with a Unix timestamp. This will create a band on the application overview chart showing queue time.

Error Reporting

The Go Agent captures errors in three different ways:

  1. the Transaction.NoticeError method
  2. panics recovered in defer Transaction.End
  3. error response status codes recorded with Transaction.WriteHeader

NoticeError

You may track errors using the Transaction.NoticeError method. The easiest way to get started with NoticeError is to use errors based on Go's standard error interface.

txn.NoticeError(errors.New("my error message"))

NoticeError will work with any sort of object that implements Go's standard error type interface -- not just errorStrings created via errors.New.

If you're interested in sending more than an error message to New Relic, the Go Agent also offers a newrelic.Error struct.

txn.NoticeError(newrelic.Error{
    Message: "my error message",
    Class:   "IdentifierForError",
    Attributes: map[string]interface{}{
        "important_number": 97232,
        "relevant_string":  "zap",
    },
})

Using the newrelic.Error struct requires you to manually marshal your error data into the Message, Class, and Attributes fields. However, there's two advantages to using the newrelic.Error struct.

First, by setting an error Class, New Relic will be able to aggregate errors in the Error Analytics section of APM. Second, the Attributes field allows you to send through key/value pairs with additional error debugging information (also exposed in the Error Analytics section of APM).

Panics

When the Transaction is ended using defer, the Transaction will optionally recover any panic that occurs, record it as an error, and re-throw it. You can enable this feature by setting the configuration:

app, err := newrelic.NewApplication(
    newrelic.ConfigAppName("Your Application Name"),
    newrelic.ConfigLicense("__YOUR_NEW_RELIC_LICENSE_KEY__"),
    func(cfg *newrelic.Config) {
        cfg.ErrorCollector.RecordPanics = true
    }
)

As a result of this configuration, panics may appear to be originating from Transaction.End.

func unstableTask(app newrelic.Application) {
    txn := app.StartTransaction("unstableTask", nil, nil)
    defer txn.End()

    // This panic will be recorded as an error.
    panic("something went wrong")
}

Error Response Codes

Setting the WebResponse on the transaction using Transaction.SetWebResponse returns an http.ResponseWriter, and you can use that returned ResponseWriter to call WriteHeader to record the response status code. The transaction will record an error if the status code is at or above 400 or strictly below 100 and not in the ignored status codes configuration list. The ignored status codes list is configured by the Config.ErrorCollector.IgnoreStatusCodes field or within the New Relic UI if your application has server side configuration enabled.

As a result, using Transaction.NoticeError in situations where your code is returning an erroneous status code may result in redundant errors. NoticeError is not affected by the ignored status codes configuration list.

Naming Transactions and Metrics

You'll want to think carefully about how you name your transactions and custom metrics. If your program creates too many unique names, you may end up with a Metric Grouping Issue (or MGI).

MGIs occur when the granularity of names is too fine, resulting in hundreds or thousands of uniquely identified metrics and transactions. One common cause of MGIs is relying on the full URL name for metric naming in web transactions. A few major code paths may generate many different full URL paths to unique documents, articles, page, etc. If the unique element of the URL path is included in the metric name, each of these common paths will have its own unique metric name.

Browser

To enable support for New Relic Browser, your HTML pages must include a JavaScript snippet that will load the Browser agent and configure it with the correct application name. This snippet is available via the Transaction.BrowserTimingHeader method. Include the byte slice returned by Transaction.BrowserTimingHeader().WithTags() as early as possible in the <head> section of your HTML after any <meta charset> tags.

func indexHandler(w http.ResponseWriter, req *http.Request) {
    io.WriteString(w, "<html><head>")
    // The New Relic browser javascript should be placed as high in the
    // HTML as possible.  We suggest including it immediately after the
    // opening <head> tag and any <meta charset> tags.
    txn := newrelic.FromContext(req.Context())
    hdr, err := txn.BrowserTimingHeader()
    if nil != err {
        log.Printf("unable to create browser timing header: %v", err)
    }
    // BrowserTimingHeader() will always return a header whose methods can
    // be safely called.
    if js := hdr.WithTags(); js != nil {
        w.Write(js)
    }
    io.WriteString(w, "</head><body>browser header page</body></html>")
}

For More Help

There's a variety of places online to learn more about the Go Agent.

The New Relic docs site contains a number of useful code samples and more context about how to use the Go Agent.

New Relic's discussion forums have a dedicated public forum for the Go Agent.

When in doubt, the New Relic support site is the best place to get started troubleshooting an agent issue.