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Tutorial04

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Roberto Abdelkader Martínez Pérez
2019-11-26 16:51:09 +01:00
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I Need My Report
================
**Junior**
Good morning!
You look very busy, what's the matter?
**Senior**
I am finishing the capacity planning report. Let me just
mail it... Done!
Today I am going to teach you how to do this report so we can split
the workload.
**Junior**
Oh. That sounds... fun. Ok, tell me about this report.
**Senior**
Here at ACME Inc. we take capacity planning seriously. It is
important that our employees always have the best resources to
accomplish their job.
We prepare a report with some statistics about the load of our
servers. This way we know when we have to buy another one.
**Junior**
I see this company scales just like Google.
**Senior**
We have a procedure:
1. SSH into the machine.
2. Execute the following commands copying its output for later fill in
the report:
- ``hostname`` and ``date``: To include in the report.
- ``free -m``: To know if we have to buy more RAM.
- ``uptime``: To see the load of the system.
- ``df -h``: Just in case we need another hard disk.
3. Copy all this in a mail and send it to *Susan*, the operations
manager.
**Junior**
And why *Susan* don't enter the server herself to see all of this?
**Senior**
She doesn't have time for this. She is a manager, she is very busy!
**Junior**
Well, I guess we can make a Kapow! endpoint to let her see all this
information from the browser. This way she doesn't need to waste any
time asking us.
I started to write it already:
.. code-block:: console
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'
**Senior**
That is preposterous!
First of all that code is not readable. And the output would be
something like.
.. code-block:: text
corporate-server
Tue 26 Nov 2019 01:03:44 PM CET
total used free shared buff/cache available
Mem: 31967 2286 23473 729 6207 28505
Swap: 0 0 0
13:03:44 up 5:57, 1 user, load average: 0.76, 0.63, 0.45
Filesystem Size Used Avail Use% Mounted on
dev 16G 0 16G 0% /dev
run 16G 1.7M 16G 1% /run
Which is also very difficult to read!
What *Susan* is used to see is more like:
.. code-block:: text
Hostname:
... the output of `hostname` ...
================================================================================
Date:
... the output of `date` ...
================================================================================
Memory:
... the output of `free -m` ...
================================================================================
... and so on ...
**Junior**
All right, what about this?
.. code-block:: console
kapow route add /capacityreport -c 'hostname | kapow set /response/body; echo ================================================================================ | kapow set /response/body; ...'
**Senior**
That fix the issue for *Susan* but make it worst for us.
What about a HEREDOC to help us make the code more readable.
**Junior**
A *HEREwhat*?
**Senior**
A HEREDOC or **here document** is the method Unix shells use to
express multi-line literals.
They look like this:
.. code-block:: console
$ cat <<HERE
you can put
more than one line
here
HERE
The shell will put the data between the first ``HERE`` and the second
``HERE`` as the ``stdin`` of the ``cat`` process.
**Junior**
If I want to use this with Kapow! I have to make it read the script
from ``stdin``. To do this I know that I have to put a ``-`` at the
end.
Let me try:
.. code-block:: bash
kapow route add /capacityreport - <<-HERE
hostname | kapow set /response/body
echo ================================================================================ | kapow set /response/body
date | kapow set /response/body
echo ================================================================================ | kapow set /response/body
free -m | kapow set /response/body
echo ================================================================================ | kapow set /response/body
uptime | kapow set /response/body
echo ================================================================================ | kapow set /response/body
df -h | kapow set /response/body
echo ================================================================================ | kapow set /response/body
HERE
**Senior**
That would work. Nevertheless I am not satisfied.
What about all the repeated ``kapow set /response/body`` statements?
Could we do any better?
**Junior**
Maybe we can redirect all to a file and use the file as the input of
``kapow set /response/body``.
**Senior**
There is a better way. You can make use of another neat ``bash``
feature: **group commands**.
Group commands allows you to execute several commands treating the
group as one single command.
You can use this way:
.. code-block:: bash
{ command1; command2; } | command3
**Junior**
What about this:
.. code-block:: bash
kapow route add /capacityreport - <<-HERE
{
hostname
echo ================================================================================
date
echo ================================================================================
free -m
echo ================================================================================
uptime
echo ================================================================================
df -h
echo ================================================================================
} | kapow set /response/body
HERE
**Senior**
I am not worried about maintaining that script. Good job!
**Junior**
You know me. Whatever it takes to avoid writing reports ;)