Logging

Logging

To provide context to each log message, structured logging is used. Thus instead of free text log messages without any specific format, the log data is to some extent divided into fields of name-value pairs, making the logs more coherent and more suitable for processing by external tools.

Log messages related to a specific HTTP request include the log field named request_id which can be used to filter out specific requests.

The log field named topic is always present and is used to separate different areas of logging. The current topics are access, messages and error, and are used to log HTTP access, debug messages and panic stack traces, respectively.

As a comparison, the topics are similar to having separate files for access logging, debug messages and errors in a conventional file-based logging system.

Log formats

When run from the command line ew-hlsingest can log in one of the formats consolepretty, consolejsonorjournalddepending on the value of the-logformatparameter. Logging can be disabled by using the valuediscard`.

$ ew-hlsingest -upstream http://127.0.0.1 -logformat consolejson

consolepretty logs to standard output (stdout) in a human-readable format. Each log line starts with the date and the log message followed by the context- dependent log fields:

2022-02-07T11:54:42Z INF Incoming request bytes_out=27592 latency_ms=6.18251 method=GET ...

consolejson logs to stdout using a JSON object for each message:

{"level":"info","topic":"access","time":"2022-02-07T12:06:07Z","bytes_out":27592, ...}

When run as a systemd service, ew-hlsingest logs directly to journaldusing thelogjournaldconfiguration parameter. When stored injournald`, field names are upper case whereas the values keep their format. Some examples:

To see entries a specific channel:

$ journalctl -u ew-hlsingest CHANNEL=ch1 -o verbose

To continuously monitor the service:

$ journalctl -fu ew-hlsingest

Log levels

At startup the log level is set to info. The log level can be changed by posting a form-field named level to the loglevel endpoint on the `ew-hlsingest server:

$ curl -F level=debug ew-hlsingest-server:8090/loglevel

The available log levels and how they relate to systemd priority values is listed below:

Log level  Systemd priority
trace      7
debug      7
info       6
warn       4
error      3
fatal      2
panic      0

To e.g. see all error and warning messages using journalctl:

$ journalctl -u ew-hlsingest PRIORITY=3 PRIORITY=4

Messages with higher level than the configured one will not be logged.