stalog

stackdriver-request-context-log

Stackdriver Logging Go library for grouping a request log and application logs.

With this library all application logs in the request are grouped and displayed under the request log (like App Engine).

Note that the interface of this library is still ALPHA level quality.
Breaking changes will be introduced frequently.

Install

go get -u github.com/gcp-kit/stalog

Example

This simple example shows how to integrate this library into your web application.

package main

import (
	"fmt"
	"net/http"
	"os"

	log "github.com/gcp-kit/stalog"
)

func main() {
	mux := http.NewServeMux()

	// Set request handler
	mux.HandleFunc("/", func(w http.ResponseWriter, r *http.Request) {
		// Get request context logger
		logger := log.RequestContextLogger(r)

		// These logs are grouped with the request log
		logger.Debugf("Hi")
		logger.Infof("Hello")
		logger.Warnf("World")

		fmt.Fprintf(w, "OK\n")
	})

	projectId := "my-gcp-project"

	// Make config for this library
	config := log.NewConfig(projectId)
	config.RequestLogOut = os.Stderr            // request log to stderr
	config.ContextLogOut = os.Stdout            // context log to stdout
	config.Severity = log.SeverityInfo          // only over INFO logs are logged
	config.AdditionalData = log.AdditionalData{ // set additional fields for all logs
		"service": "foo",
		"version": 1.0,
	}

	// Set middleware for the request log to be automatically logged
	handler := log.RequestLogging(config)(mux)

	// Run server
	fmt.Println("Waiting requests on port 8080...")
	if err := http.ListenAndServe(":8080", handler); err != nil {
		panic(err)
	}
}

When this application receives a HTTP request GET /, following logs will be logged (with pretty print for display purposes only).

// STDOUT
{
  "time": "2018-10-10T16:46:07.476567+09:00",
  "logging.googleapis.com/trace": "projects/my-gcp-project/traces/a8cb3e640add456cf7ed58e4a0589ea0",
  "logging.googleapis.com/sourceLocation": {
    "file": "main.go",
    "line": "21",
    "function": "main.main.func1"
  },
  "severity": "INFO",
  "message": "Hello",
  "data": {
    "service": "foo",
    "version": 1
  }
}
{
  "time": "2018-10-10T16:46:07.476806+09:00",
  "logging.googleapis.com/trace": "projects/my-gcp-project/traces/a8cb3e640add456cf7ed58e4a0589ea0",
  "logging.googleapis.com/sourceLocation": {
    "file": "main.go",
    "line": "22",
    "function": "main.main.func1"
  },
  "severity": "WARNING",
  "message": "World",
  "data": {
    "service": "foo",
    "version": 1
  }
}

// STDERR
{
  "time": "2018-10-10T16:46:07.47682+09:00",
  "logging.googleapis.com/trace": "projects/my-gcp-project/traces/a8cb3e640add456cf7ed58e4a0589ea0",
  "severity": "WARNING",
  "httpRequest": {
    "requestMethod": "GET",
    "requestUrl": "/",
    "requestSize": "0",
    "status": 200,
    "responseSize": "3",
    "userAgent": "curl/7.58.0",
    "remoteIp": "[::1]:61352",
    "serverIp": "192.168.86.31",
    "referer": "",
    "latency": "0.000304s",
    "cacheLookup": false,
    "cacheHit": false,
    "cacheValidatedWithOriginServer": false,
    "protocol": "HTTP/1.1"
  },
  "data": {
    "service": "foo",
    "version": 1
  }
}

The log format is based on LogEntry's structured payload so that you can pass these logs to Stackdriver Logging agent.

Stackdriver Logging agent setting

GKE

No settings required. All logs from STDOUT and STDERR are collected by default agents.

GCE

For GCE, you have to install agents manually (docs).
Please install them and create config file like following,

# request log
<source>
    @type tail
    format json
    path /tmp/my_request_log
    pos_file /var/lib/google-fluentd/pos/my-request-log.pos
    read_from_head true
    time_format %Y-%m-%dT%H:%M:%S.%N%Z
    tag my-request-log
</source>

# app log
<source>
    @type tail
    format json
    path /tmp/my_app_log
    pos_file /var/lib/google-fluentd/pos/my-app-log.pos
    read_from_head true
    time_format %Y-%m-%dT%H:%M:%S.%N%Z
    tag my-app-log
</source>

Don't forget to specify time_format %Y-%m-%dT%H:%M:%S.%N%Z to each <source></source> directive.

How logs are grouped

This library leverages the grouping feature of Stackdriver Logging. See following references fore more details.

• https://godoc.org/cloud.google.com/go/logging#hdr-Grouping_Logs_by_Request
• https://cloud.google.com/appengine/articles/logging#linking_app_logs_and_requests

Disclaimer

This is not an official Google product.