Structure logs for human and computer

Get pretty good readability for human, computer, grep, Logstash… Even if the raw data is not being optimal for either, this can be improved by diplaying a reformatted colorized output (human) or by exporting to JSON/CBOR/…

Logfmt - Historical log format in this spirit https://brandur.org/logfmt

time="2015-03-26T01:27:38-04:00" level=info msg="Stopping all fetchers"         tag=stopping_fetchers  module=kafka.consumer.ConsumerFetcherManager  id=ConsumerFetcherManager-1382721708341
time="2015-03-26T01:27:38-04:00" level=info msg="Performing log compaction"     tag=log_compaction     module=kafka.compacter.LogCompactionManager
time="2015-03-26T01:27:38-04:00" level=info msg="Performing garbage collection" tag=gc                 module=kafka.cleaner.GarbageCollectionManager
time="2015-03-26T01:27:38-04:00" level=info msg="Starting all fetchers"         tag=starting_fetchers  module=kafka.consumer.ConsumerFetcherManager id=ConsumerFetcherManager-1382721708341

Logrus - Battle tested logger for Go https://github.com/sirupsen/logrus
Zerolog - Better performance by reducing memory allocation for Go https://github.com/rs/zerolog
Zap :zap: - Also targeting a great performance for Go https://github.com/uber-go/zap
Log - Another logger for Go https://github.com/apex/log
Emodebug 🤩 - Dart logger with emojis https://github.com/synw/emodebug

Log level meaning

Depending on the historical engineering culture, systems share similar log levels, but with some differences. Below is a great list of log levels that your application may use:

Level	Short name	Description
FATAL	FAT	La source de l’arrêt de l’application, utile pour trouver l’origine de l’arrêt dans tous les logs
ERROR	ERR	Une erreur que le développeur ne sait pas comment la gérer => Quand on aura une bonne implémentation, cela deviendra une alerte (WARNING)
WARNING	WRN	Une erreur que l’application sait gérer
NOTICE	NOT	Un changement d’état de l’application (Init, Ready, Stopping…) ou des données (Open, Frozen…), ceci peut être représenté par des émoticônes comme implémenté par Emodebug
INFO	INF
DEBUG	DBG
TRACE	TRC	Chaque fonction, avec optionnellement ses paramètres INPUT et sa sortie OUTPUT

See more about syslog and Log4J log levels

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The syslog protocol

The syslog is defined by the RFC 5424. The data is structured within each log line as the following:

Structured data in one log line

See how your application can structure log data in order to be powerfully processed by log analysis tools.