StackdriverLogging

A SwiftLog LogHandler that logs GCP Stackdriver formatted JSON to a file.

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

Dependencies

This Stackdriver LogHandler has a dependency 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:"2.0.0")

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

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

Bootstrapping

A factory is used to instantiate StackdriverLogHandler instances. Before bootstrapping your LoggingSystem, you must first call the StackdriverLogHandlerFactory.prepare(:) function with a StackdriverLoggingConfiguration, an NIO NonBlockingFileIO to write the logs asynchronously and an EventLoopGroup used to process new log entries in the background.

You are responsible for gracefully shutting down the NIO dependencies used to prepare the StackdriverLogHandlerFactory.

Here's an example of how this works:

let config = StackdriverLoggingConfiguration(logFilePath: "var/log/myapp.log", defaultLogLevel: "debug")

let threadPool = NIOThreadPool(numberOfThreads: NonBlockingFileIO.defaultThreadPoolSize)
threadPool.start()
let fileIO = NonBlockingFileIO(threadPool: threadPool)
let eventLoopGroup = MultiThreadedEventLoopGroup(numberOfThreads: NonBlockingFileIO.defaultThreadPoolSize)

StackdriverLogHandlerFactory.prepare(with: configuration,
                                     fileIO: fileIO,
                                     eventLoopGroup: eventLoopGroup)

LoggingSystem.bootstrap { label -> LogHandler in
    return StackdriverLogHandlerFactory.make()
}

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:

var logger = 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"
}

Stackdriver logging agent + fluentd config

You must use this LogHandler 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.

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>

Future

A Stackdriver gRPC API based implementation is being considered.