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+++
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title = "Things I Learnt The Hard Way - Logs Are For Events, Not User Interface"
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date = 2019-07-01
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[taxonomies]
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tags = ["en-au", "books", "things i learnt", "logs", "ui"]
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+++
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Two things in one: First of all, when using logging, use it to log events, not
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for user interfaces; second, log _events_ in a machine readable way, not
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necessarily an human readable format.
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<!-- more -->
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For a long time, I used logs to show to the user what was happening. To me, it
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was logical to use something where I could mark errors as errors, general
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information as information and, if the user requested more information, print
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more information on what was going on. So I just added logging, defined normal
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messages as `info`, errors as `errors`, information that may help me find
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errors as `debug` and use _only_ the logging system for all output of the
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application.
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But that's not what logs are targeted for -- and now I'm having to rethink
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most of the stuff I already wrote.
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Use the standard output to inform the user what's going on, in a human
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readable format; use the standard error output to inform the user when things
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go wrong; but use the logs to capture something that you'll have to process
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later, so you should probably use a format that it is easier to parse, even if
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it is not so friendly.
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As an example, let's say you're connecting to a server. You could use the
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standard output to say "Connecting to server", to give the user a feedback
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about what's going on; at the same time, you could log "CONNECTION
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[SERVER]", with the IP/Name of the server you're connecting. Surely, the
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"CONNECTION" word is not that friendly to the user, but if you had to parse
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the line, it would be really easy, wouldn't it?
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Another example: If your application is adding a record to the database, there
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is nothing wrong logging "ADDING_RECORD: field=value; field=value;
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field=value" 'cause, in case something goes wrong while saving the record, you
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could have the values to try to figure out why it failed -- surely, logging
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why it failed also helps, but you know what I mean. This is an example of
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something that makes complete sense in logs, but not in user interfaces.
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{{ chapters(prev_chapter_link="/books/things-i-learnt/config-file", prev_chapter_title="The Config File Is Friend", next_chapter_link="/books/things-i-learnt/monitoring", next_chapter_title=Learn To Monitor"") }}
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