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Terminal Tip: a CF remote monitor script

(Find more terminal tips here: https://blogs.sap.com/tag/terminaltip/)

In the previous terminal tip (remotely monitor a CF deployment) we saw the building blocks of how we might go about finding and then remotely monitoring an ongoing multi-target application (MTA) operation.

On today’s #HandsOnSAPDev live stream, Ep.66, we wrote a script mtaopsmon that put these building blocks together (check out the section of the replay starting at around 14:55). I thought it would be worth sharing that script here, and explaining it bit by bit.

First, let’s see the script in its entirety:

#!/usr/bin/env bash

getopsid () { cf mta-ops | sed '1,3d' | head -1 | awk '{print $1}'; }                                                                   

echo -n Searching for MTA operation

mtaopid=$(getopsid)

while [[ -z ${mtaopsid} ]]
do
  echo -n .
  sleep 1
  mtaopsid=$(getopsid)
done

echo
echo MTA operation found: ${mtaopsid}

cf deploy -i ${mtaopsid} -a monitor

Now let’s take it a step at a time.

Step 1 – Defining a function to get an MTA operation ID

The first line looks like this:

getopsid () { cf mta-ops | sed '1,3d' | head -1 | awk '{print $1}'; }                                                                   

Here we’re defining a function getopsid that contains way to try and grab the ID of an MTA operation. This is deliberately over simplified but works for our purposes, and is a good start.

If you consider what the output of cf mta-ops gives for when there’s an operation (or more than one), it looks like this:

Getting active multi-target app operations in org p200135114trial / space dev as qmacro+workflowcodejam@example.com...
OK
id                                     type     mta id                  status    started at                      started by
acb3bcda-8b7b-11ea-bb72-eeee0a890182   DEPLOY   sample.onboarding.mta   RUNNING   2020-05-01T07:16:28.294Z[UTC]   qmacro+workflowcodejam@example.com

There’s a couple of descriptive lines (“Getting …” and “OK”), followed by a column header line (“id …”) and then a line with the details of an operation, where the first column is the operation’s ID (“acb3…”).

If you consider what the output looks like when there are no operations, it looks like this:

Getting active multi-target app operations in org p200135114trial / space dev as qmacro+workflowcodejam@example.com...
OK
No multi-target app operations found

Now we know what the two possible outputs look like, we can stare at the first line of our script and understand what getopsid does. It calls cf mta-ops, and pipes the output into sed '1,3d‘, which will simply delete the first three lines. Whatever then remains is either nothing (there are only three lines when there are no MTA operations) or a list of operation details:

acb3bcda-8b7b-11ea-bb72-eeee0a890182   DEPLOY   sample.onboarding.mta   RUNNING   2020-05-01T07:16:28.294Z[UTC]   qmacro+workflowcodejam@example.com

To keep things simple in this case, we’re just going to take the first operation, in case there are more, and so we pipe the remaining line(s) into head -1 which will just give us the first line.

Finally, we pipe that line into awk '{print $1}' which will return just the first “field”, i.e. the operation ID (“acb3…”).

So basically, calling this function getopsid will return either an operation ID, or nothing.

Step 2 – Looping until we get an MTA operation ID

Here’s the next part:

echo -n Searching for MTA operation

mtaopid=$(getopsid)

while [[ -z ${mtaopsid} ]]
do
  echo -n .
  sleep 1
  mtaopsid=$(getopsid)
done

After printing out “Searching for MTA operation”, without a newline (that’s what the -n option to echo means), we call getopsid and assign whatever it returns to the mtaopid variable, which will therefore contain an ID, or nothing.

Then we loop around, as long as the -z ${mtaopsid} condition is true, i.e. for as long as there’s no value in the mtaopsid variable. Inside the loop, we print a “.” character, sleep for a second, and then call the getopsid function again.

This will run therefore until we get an MTA operation ID.

Step 3 – Attaching to and monitoring the MTA operation

Once we have an MTA operation ID, we can use the technique we learned about in the previous terminal tip to attach to an ongoing operation, and call the ‘monitor’ action upon it:

echo
echo MTA operation found: ${mtaopsid}

cf deploy -i ${mtaopsid} -a monitor

And that’s it!

Here’s an example of the script in action, showing a few lines from the log output. To take this screenshot, I started the mtaopsmon script up, then switched over to the SAP Web IDE to deploy the “sample.onboarding.mta” MTA that I’d previously built.


Next steps

Of course, the function that gets the MTA operation ID is deliberately very simple at this stage (we wrote the script together during the live stream). Have a think about how you could improve that – what would happen (and what would we want to do) if there were multiple operations? Let me know your thoughts in the comments, and until next time …

Share & enjoy, and remember, #TheFutureIsTerminal!

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