Prometheus Label Bookmarklet Rabbit Hole
Following on from my previous post where I showed the bookmarklet I created to allow users to persist labels on Prometheus' targets page, I wanted to write a post explaining how I arrived at the point of the bookmarklet.
Quick summary of the problem, I saw the “before” labels as a means of deciding what relabel configurations I wanted to introduce into each scrape configuration I was creating, however the “before” labels were only visible during a mouseover event which was frustrating me no end.
Digging into the source code to understand how the mouseover tooltip is generated, I noticed that the list of “before” labels was not a dynamic page element, the content of the tooltip is embedded within the pages' HTML, so I knew I just needed a way to get to the underlying HTML.
Initially this was achieved using the inspect element tool, this was ok if a bit clunky.
While inspecting the list of labels I noticed a snippet of code
data-toggle="tooltip", surely we could change
for something else.
It just so happens that Bootstrap can provide a number of components to your page, I didn’t really know what I was after at the time so there was a bit of trial and error involved in finding the component with the behaviour that would suit my use case, but eventually I came across Popovers and they seemed to do what I wanted. The example code provided in the documentation also looked pretty similar to the tooltip code, so it felt like a pretty good replacement.
I assumed that since the tooltip functionality worked on labels, the jQuery selector for all
'[data-toggle="tooltip"]' was working, but no harm in verifying
Ok great, so can we change the
tooltip() method for
That seemed to work nicely and I was quite content to stop there initially. However, as I started to make use of these popovers I quickly noticed that the default popover width wasn’t large enough and made reading label lists quite difficult as they spanned multiple lines a lot of the time.
I noticed that when the popover is created, a new
div is inserted into the DOM with a class of
class="popover fade bs-popover-right show", inspecting this element in the console I also noticed there was a
max-width attribute defaulting to
276px. What if I were to change that value?
Perfect, well almost…See the problem is, if that DOM element doesn’t exist, the CSS change can’t take effect. In practice this meant every time I opened up a new popover, I’d have to re-run the CSS change.
This could probably suffice for personal usage, it didn’t have to be perfect, but I’ve come this far and since I saw some use in what I was doing I thought to take it a step further and create something for folk across the organisation to use without having to copy and paste snippets every time they loaded the targets page.
First thing’s first, I had to find all the labels on the page and add an EventListener to them.
Next up was to package the commands I was running manually into a function which would be called each time the
addEventListener is triggered.
For some reason, this didn’t work as I expected, what I noticed was that on the initial click, the popover would stay at
276px size, and subsequent popovers would be sized correctly at
Thinking through why this might be happening I remembered that the popover element is inserted into the DOM when created,
myFunction was called on the initial click the jQuery library wasn’t able to find any elements with a
To combat this I added a slight delay of 100ms before editing CSS attributes of the popover using the
At this point I had a small script that did what was needed, so it was time to package it into a bookmarklet so it could be saved and used on the appropriate page. I can’t remember what tool I used to achieve this, but a quick search provides more than enough tools which achieve the same result.
There probably is a bit of cleanup and best practice I should make sure I am following, maybe even add some defensive code so that the bookmarklet would only run the script on designated pages, but since the current user count is 1… it’s probably a little much at this point in time 😄
And with that, thanks for reading.