Add new LogFormat: StructuredJSON

[akshaymankar]

This format is intended as an imporvement over the JSON format. It tries to
improve in these ways:

• Explicitly encode log level as a key in the main JSON object logged

• Encode field values as key-value pairs in the main JSON object

Encoding logs like this makes it easy for external tools like fluent-bit and
elasticsearch to understand the log level and the fields and index them as such
without requiring bonanza to be present while processing logs.

https://wearezeta.atlassian.net/browse/FS-62

Checklist

• The PR Title explains the impact of the change.
• The PR description provides context as to why the change should occur and what the code contributes to that effect. This could also be a link to a JIRA ticket or a Github issue, if there is one.
• changelog.d contains the following bits of information (details):
  • A file with the changelog entry in one or more suitable sub-sections. The sub-sections are marked by directories inside changelog.d.

[jschaul]

This just adds the new log format, right? But doesn't turn it on anywhere yet - how/where is it turned on to log that way?

The first part, the log level - could that not also be a separate structural element rather than the first item in the list of msgs? Or do you configure fluent-bit to parse the log level as first element?

[akshaymankar]

This just adds the new log format, right? But doesn't turn it on anywhere yet - how/where is it turned on to log that way?

Yes, it only adds a new log format. I will turn it on in our federation environments as a test. If all looks fine after a month or so, I will propose that we make it the default.

The first part, the log level - could that not also be a separate structural element rather than the first item in the list of msgs? Or do you configure fluent-bit to parse the log level as first element?

The way tinylog works, it sends all the logs as [Element] to the renderer, this does contain the log level encoded as 1 character string (I, D, etc.). But it also sends the log level separately. Instead of relying on this contract of parsing the first 1 character string, I decided to just ignore it and put the log level separately sent by tiny log into the final JSON as level. I will comment inline to show where. This ensures that no configuration on fleunt-bit is required.

[akshaymankar]

@jschaul This line adds the level to the final JSON.

[jschaul]

Cool, thanks!

[akshaymankar]

Turns out this doc is a lie. The actual LogLevel passed here is just the configured setting, so all logs are currently being marked whatever log level is configured for the service 🤦
The only way to get the log level of the event is to parse it from the list of messages. I will create a follow up PR.

[akshaymankar]

I also created an issue upstream: https://gitlab.com/twittner/tinylog/-/issues/5