# Logging

The backend logging system is built on bunyan and is designed for categorised, hierarchical logging with log thresholds.

Each log treshold has a corresponding method with the same name available on a logger instance. The possible log thresholds are:

• trace - for very low-level messages that you normally don't need to see.
• debug - for messages that can help with debugging issues.
• info - for general messages that you want to see in the logs in production.
• warn - for minor issues that don't cause problems but may need investigating.
• error - for problems and errors that need to be investigated and/or fixed.

For example, to create a logger which logs to console:

import { createLog } from '@/backend/logging'

const log = createLog({
  name: 'root',
  logLevel: 'debug'
})

// will output nothing since minimum log level is "debug"
log.trace('test') 

// will output: 19:36:13.090Z  DEBUG root: test
log.debug('test') 

Now a child logger can be created from the root logger:

const child = log.create('sub')

// will output: 19:36:14.090Z  DEBUG root/sub: test2
child.debug('test2')

Log messages will be sent to Datadog if the following environment variables are set:

• DATADOG_API_KEY
• DATADOG_APPLICATION_KEY

See https://github.com/DataDog/datadog-api-client-typescript for information on these parameters.