229 lines
6.6 KiB
ReStructuredText
229 lines
6.6 KiB
ReStructuredText
I Need my Report
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================
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**Junior**
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Good morning!
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You look very busy, what's going on?
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**Senior**
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I am finishing the capacity planning report. Let me just mail it... Done!
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Today I am going to teach you how to write this report so we can split the
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workload.
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**Junior**
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Oh. That sounds... fun. OK, tell me about this report.
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**Senior**
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Here at ACME Inc. we take capacity planning seriously. It is
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important that our employees always have the best resources to
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accomplish their job.
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We prepare a report with some statistics about the load of our
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servers. This way we know when we have to buy another one.
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**Junior**
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I see this company scales up just like Google...
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**Senior**
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Smartass...
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**Junior**
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(chuckles)
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**Senior**
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We have a procedure:
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1. ``ssh`` into the machine.
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2. Execute the following commands copying its output for later filling in the
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report:
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- ``hostname`` and ``date``: To include in the report.
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- ``free -m``: To know if we have to buy more RAM.
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- ``uptime``: To see the load of the system.
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- ``df -h``: Just in case we need another hard disk drive.
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3. Copy all this in an email and send it to *Susan*, the operations manager.
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**Junior**
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And why *Susan* can't ``ssh`` into the server herself to see all of this?
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**Senior**
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She doesn't have time for this. She is a manager, and she is very busy!
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**Junior**
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Well, I guess we can make a *Kapow!* endpoint to let her see all this
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information from the browser. This way she doesn't need to waste any time
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asking us.
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I started to write it already:
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.. code-block:: console
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kapow route add /capacityreport -c 'hostname | kapow set /response/body; date | kapow set /response/body; free -m | kapow set /response/body; uptime | kapow set /response/body; df -h | kapow set /response/body'
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**Senior**
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Not good enough!
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First of all, that code is not readable. And the output would be something
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like:
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.. code-block:: text
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corporate-server
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Tue 26 Nov 2019 01:03:44 PM CET
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total used free shared buff/cache available
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Mem: 31967 2286 23473 729 6207 28505
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Swap: 0 0 0
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13:03:44 up 5:57, 1 user, load average: 0.76, 0.63, 0.45
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Filesystem Size Used Avail Use% Mounted on
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dev 16G 0 16G 0% /dev
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run 16G 1.7M 16G 1% /run
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Which is also very difficult to read!
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What *Susan* is used to see is more like this:
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.. code-block:: text
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Hostname:
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... the output of `hostname` ...
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================================================================================
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Date:
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... the output of `date` ...
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================================================================================
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Memory:
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... the output of `free -m` ...
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================================================================================
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... and so on ...
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**Junior**
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All right, what about this?
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.. code-block:: console
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kapow route add /capacityreport -c 'hostname | kapow set /response/body; echo ================================================================================ | kapow set /response/body; ...'
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**Senior**
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That fixes the issue for *Susan*, but makes it worse for us.
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What about a HEREDOC to help us make the code more readable?
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**Junior**
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A *HEREwhat*?
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**Senior**
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A HEREDOC or **here document** is the method Unix shells use to
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express multi-line literals.
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They look like this:
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.. code-block:: console
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$ cat <<-'EOF'
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you can put
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more than one line
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here
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EOF
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The shell will put the data between the first ``EOF`` and the second
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``EOF`` as the ``stdin`` of the ``cat`` process.
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**Junior**
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OK, I understand. That's cool, by the way.
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So, if I want to use this with *Kapow!*, I have to make it read the script
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from ``stdin``. To do this I know that I have to put a ``-`` at the end.
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Let me try:
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.. code-block:: bash
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kapow route add /capacityreport - <<-'EOF'
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hostname | kapow set /response/body
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echo ================================================================================ | kapow set /response/body
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date | kapow set /response/body
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echo ================================================================================ | kapow set /response/body
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free -m | kapow set /response/body
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echo ================================================================================ | kapow set /response/body
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uptime | kapow set /response/body
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echo ================================================================================ | kapow set /response/body
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df -h | kapow set /response/body
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echo ================================================================================ | kapow set /response/body
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EOF
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**Senior**
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That would work. Nevertheless I am not yet satisfied.
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What about all the repeated ``kapow set /response/body`` statements?
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Do you think we could do any better?
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**Junior**
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Maybe we can redirect all output to a file and use the file as the input of
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``kapow set /response/body``.
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**Senior**
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There is a better way. You can make use of another neat ``bash`` feature:
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**group commands**.
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Group commands allows you to execute several commands treating the
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group as one single command.
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You can use this way:
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.. code-block:: bash
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{ command1; command2; } | command3
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**Junior**
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What about this:
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.. code-block:: bash
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kapow route add /capacityreport - <<-'EOF'
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{
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hostname
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echo ================================================================================
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date
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echo ================================================================================
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free -m
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echo ================================================================================
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uptime
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echo ================================================================================
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df -h
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echo ================================================================================
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} | kapow set /response/body
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EOF
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**Senior**
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Nice! Now I am not worried about maintaining that script. Good job!
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**Junior**
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You know me. Whatever it takes to avoid writing reports ;-)
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(both chuckle).
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