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:"1.0.1")

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

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

Bootstrapping

Here is an example of how a StackdriverLogHandler could be bootstrapped, notice that the StackdriverLogHandler initializer will throw if it receives an invalid filepath.

LoggingSystem.bootstrap { label -> LogHandler in
    // ...
    if label == "Stackdriver" {
        do {
            var logHandler = try StackdriverLogHandler(logFilePath: "/var/log/my_app.log")
            logHandler.logLevel = .error
            return logHandler
        } catch {
            // The logFilePath does not exist or is inacessible, defaulting to a console logger
            print("Failed to create a StackdriverLogHandler with error: '\(error.localizedDescription)'")
            return ConsoleLogger()
        }
    }
    // ...
}    

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 can 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>