StackdriverLogging

A SwiftLogLogHandler that logs GCP Stackdriver formatted JSON.

For more information on Stackdriver structured logging, see: https://cloud.google.com/logging/docs/structured-logging and LogEntry

Dependencies

This Stackdriver LogHandler depends on SwiftNIO which is used to create and save your new log entries in a non-blocking fashion.

How to install

Swift Package Manager

.package(url:"https://github.com/Brainfinance/StackdriverLogging.git", from:"4.0.0"),

In your target's dependencies add "StackdriverLogging" e.g. like this:

.target(name:"App", dependencies:["StackdriverLogging"]),

Vapor 4

Here's a bootstrapping example for a standard Vapor 4 application.

import App
import Vapor
varenv=tryEnvironment.detect()tryLoggingSystem.bootstrap(from:&env){(logLevel)->(String)->LogHandlerinreturn{ label ->LogHandlerinvarlogger=StackdriverLogHandler(destination:.stdout)
logger.logLevel = logLevel
return logger
}}letapp=Application(env)defer{ app.shutdown()}tryconfigure(app)try app.run()

Logging JSON values using Logger.MetadataValue

To log metadata values as JSON, simply log all JSON values other than String as a Logger.MetadataValue.stringConvertible and, instead of the usual conversion of your value to a String in the log entry, it will keep the original JSON type of your values whenever possible.

For example:

varlogger=Logger(label:"Stackdriver")logger[metadataKey:"jsonpayload-example-object"]=["json-null":.stringConvertible(NSNull()),"json-bool":.stringConvertible(true),"json-integer":.stringConvertible(1),"json-float":.stringConvertible(1.5),"json-string":.string("Example"),"stackdriver-timestamp":.stringConvertible(Date()),"json-array-of-numbers":[.stringConvertible(1),.stringConvertible(5.8)],"json-object":["key":"value"]]
logger.info("test")

Will log the non pretty-printed representation of:

{ "sourceLocation":{ "function":"boot(_:)",
"file":"\/Sources\/App\/boot.swift",
"line":25
},
"jsonpayload-example-object":{ "json-bool":true,
"json-float":1.5,
"json-string":"Example",
"json-object":{ "key":"value"
},
"json-null":null,
"json-integer":1,
"json-array-of-numbers":[ 1,
5.8
],
"stackdriver-timestamp":"2019-07-15T21:21:02.451Z"
},
"message":"test",
"severity":"INFO"
}

Logging from a managed platform

If your app is running inside a managed environment such as Google Cloud Run or a container based Compute Engine, logging to stdout should get you up and running automatically.

Stackdriver logging agent + fluentd config

If you prefer logging to a file, you can use a file destination StackdriverLogHandler.Destination.file in combination with the Stackdriver logging agent https://cloud.google.com/logging/docs/agent/installation and a matching json format google-fluentd config (/etc/google-fluentd/config.d/example.conf) to automatically send your JSON logs to Stackdriver for you.

Here's an example google-fluentd conf file that monitors a json based logfile and send new log entries to Stackdriver:

<source>
@type tail
# Format 'JSON' indicates the log is structured (JSON).
format json
# The path of the log file.
path /var/log/example.log
# The path of the position file that records where in the log file
# we have processed already. This is useful when the agent
# restarts.
pos_file /var/lib/google-fluentd/pos/example-log.pos
read_from_head true
# The log tag for this log input.
tag exampletag
</source>