+++
title = "Things I Learnt The Hard Way - Logs Are For Events, Not User Interface"
date = 2019-07-01

[taxonomies]
tags = ["en-au", "books", "things i learnt", "logs", "ui"]
+++

Two things in one: First of all, when using logging, use it to log events, not
for user interfaces; second, log _events_ in a machine readable way, not
necessarily an human readable format.

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For a long time, I used logs to show to the user what was happening. To me, it
was logical to use something where I could mark errors as errors, general
information as information and, if the user requested more information, print
more information on what was going on. So I just added logging, defined normal
messages as `info`, errors as `errors`, information that may help me find
errors as `debug` and use _only_ the logging system for all output of the
application.

But that's not what logs are targeted for -- and now I'm having to rethink
most of the stuff I already wrote.

Use the standard output to inform the user what's going on, in a human
readable format; use the standard error output to inform the user when things
go wrong; but use the logs to capture something that you'll have to process
later, so you should probably use a format that it is easier to parse, even if
it is not so friendly.

As an example, let's say you're connecting to a server. You could use the
standard output to say "Connecting to server", to give the user a feedback
about what's going on; at the same time, you could log "CONNECTION
[SERVER]", with the IP/Name of the server you're connecting. Surely, the
"CONNECTION" word is not that friendly to the user, but if you had to parse
the line, it would be really easy, wouldn't it?

Another example: If your application is adding a record to the database, there
is nothing wrong logging "ADDING_RECORD: field=value; field=value;
field=value" 'cause, in case something goes wrong while saving the record, you
could have the values to try to figure out why it failed -- surely, logging
why it failed also helps, but you know what I mean. This is an example of
something that makes complete sense in logs, but not in user interfaces.

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