Bug 1911824

Description of problem:
Dashboard has been removed.  To me, this is a fundamental and the most useful feature of cockpit.
Specifically, dashboard provides a view of all monitored machines on a common timeline.
Dashboard makes it very easy to spot, at a glance, any resource problem on one or more machines.
All of the other features, that show or change behaviour, whether graphical or text listing, are only available
on a per machine basis.  Hence there is no great value in cockpit because one might as well connect that machine
of concern and perform the same monitoring/adjusting tasks natively on that machine.

https://cockpit-project.org/blog/cockpit-234.html
  The dashboard has been removed
  Due to limited functionality, the dashboard page has been removed. Connecting to additional hosts is directly
  available in the Shell without the need for a separate package. The dashboard graphs were not providing enough
  information to be useful and were implemented with a performance cost on the servers and the browser. Individual
  machine metrics are available on a separate page on the Overview page. Multi-host monitoring is handled better
  by other tools (e.g. Grafana), which provide more useful data.

I can see the rationale which led to the dashboard being removed, but I wonder if the perspective for
consideration was unsufficiently universal.  Let me elaborate on a point by point basis:
Limited functionality: dashboard did one thing, it did it well; it presented a simulataneous view of multiple machines.
Not enough information to be useful: but dashboard did provide sufficient information to be useful for
quickly identifying a hot-spot or resource problem on a single page.
Connection to additional hosts: connecting to additional hosts, individually via the Shell is indeed possible,
but getting information collectively and displaying that graphically is a different matter.
Performance cost: any collective monitoring facility is going to have a performance impact on each of the servers
being monitored, the real question is if that cost is acceptable given the gains. In my opinion, being able to spot
a problem before becoming critical or causing a crash is definitly justifiable.  The performance cost on the browser
is a different question.  Indeed the cost on the browser server is very high.  However, by deploying the cockpit
dashboard a server dedicated purely to admin and monitoring means good monitoring performance and low impact on
the machines being monitored.
Individual metrics: these are still available, but the dashboard feature is about collective rather than individaul
metrics and hence I fail to understand why this is stated as a reason for removing the dashboard.
Better handled by other tools: even if the display might be handled better, the fundamental property of collecting
metrics from multiple machines and displaying a (albeit minimal) collective summary was something that
cockpit-dashboard did very well, and is unique to cockpit.  The suggested Grafana does not appear to do the metric
gathering from multiple machines like cockpit does.  Cockpit-dashboard provides a self-contained gathering and display of collective
metrics without requiring significant effort to comprehend, configure and control the graphic interface.

I would welcome counter arguments from the developers or other suggestions to meet this single requirement:
display metrics from multiple servers on a single page timeline.

Version-Release number of selected component (if applicable):
  systemctl info cockpit
  Installed Packages
  Name         : cockpit
  Version      : 234
  Release      : 1.fc33
  Architecture : x86_64
  Size         : 55 k
  Source       : cockpit-234-1.fc33.src.rpm
  Repository   : @System
  From repo    : updates
  Summary      : Web Console for Linux servers
  URL          : https://cockpit-project.org/
  License      : LGPLv2+
  Description  : The Cockpit Web Console enables users to administer GNU/Linux servers using a
               : web browser.
               : 
               : It offers network configuration, log inspection, diagnostic reports, SELinux
               : troubleshooting, interactive command-line sessions, and more.

How reproducible:
100% on latest version 234


Steps to Reproduce:
1. https://localhost:9090/dashboard


Actual results:
Not found!


Expected results:
Graphs showing a summary of activity for all monitored machines,
ideally a vertical stack (with a corresponding horizontal timeline)
with one graph each for CPU, Memory, Network and Disk I/O.
Additional graphs for % disk space across all monitored machines would be useful
(but with the x-axis as disk partition rather than time)
That way, a single glance can show immediately if any one machine is suffering a resource problem.

Additional info:
Graphical views have been gradually changing over the last year or so, and dropping the most useful features.
Moving graphs from being a vertical stack to side-by-side removes the ability to visibly align events on a common
timeline.  When graphs are stacked veritically, the corresponding event for each graph aligns vertically and,
for instance, high Disk I/O activity and high Network activity often occur at the same time.