CW Logger

A small library intended to be used for logging to Cloud Watch Logs.

By default it logs as JSON.

Initialise the logger with the AWS Request ID and Lambda name, you can find the Request ID in the lambda context and the Lambda name you can get from the runtime environment variable AWS_LAMBDA_FUNCTION_NAME.

There is no need to set a value in EventTime the logger will set the current time in the correct format by it self.

For INFO messages the only required field to fill in is Message, all the other required fields will be added by the logger.

For ERROR messages the ErrorCode field should also be filled in, if it is not then it will default to the contents of the Message property which is not ideal.

When an ERROR is logged the Action field is also required, however it will default to Open if it is not set, so you only need too set it if you intend to use any other action such as Update or Close.

The default log message looks like the following.

type LogEntry struct {
	EventTime    string                 `json:"eventTime"`
	Message      string                 `json:"message"`
	SourceName   string                 `json:"sourceName"`
	ErrorCode    string                 `json:"errorCode,omitempty"`
	ErrorMessage string                 `json:"errorMessage,omitempty"`
	RequestID    string                 `json:"requestId"`
	LogLevel     string                 `json:"logLevel"`
	Keys         map[string]interface{} `json:"keys,omitempty"`
	Action       AlertAction            `json:"alertAction,omitempty"`
}

It will marshal into

{
    "eventTime": "2019-01-02T15:04:05.12345Z",
    "message": "A message",
    "sourceName": "The Source",
    "errorMessage": "something",
    "requestId": "asdasd-asd123-sasad-asd",
    "logLevel": "INFO",
    "keys": {
        "somekey": "asd"
    }
}

Leaving ErrorMessage empty will omit the property from the marshalled message.

A map called Keys can be used to add custom fields to the log message. There is a helper function to set the values in the map when needed.

DEBUG logging

There is possible to create DEBUG level logging. DEBUG logging is only active when the log is inInitialized with InitWithDebugLevel() and the debugEnabled parameter is true. This can be used to switch the debug logging on/off, for example in test vs prod environments.

Logging Session Values

Sometimes you may want to log the same value in Keys pretty much all the time. For instance when working with an order you might want to log the order number as soon as you know what it is.

The WithKeysValue function exists to assist with this. Call it once with the value you want to add, and it will be added to all log statements thereafter.

Note that it will overwrite anything that has the same key.

func doStuff() {
	logger.WithKeysValue("myKey", "important")
	
	logger.InfoString("my message")
}

The output of the InfoString would look something like

{
    "eventTime": "2019-01-02T15:04:05.12345Z",
    "message": "my message",
    "sourceName": "The Source",
    "requestId": "asdasd-asd123-sasad-asd",
    "logLevel": "INFO",
    "keys": {
        "myKey": "important"
    }
}