Title: NixOS Bento: now able to compare local and remote NixOS version
       Author: Solène
       Date: 06 September 2022
       Tags: bento nixos nix
       Description: 
       
       # Bento
       
       Project update: the report is now able to compare if the remote server
       is using the NixOS version we built locally.  This is possible as NixOS
       builds are reproducible, I get the same result on the server and the
       remote system.
       
       The tool is getting in a better shape, the code received extra checks
       in a lot of place.
       
       A bit later (blog post update), I added the possibility to trigger the
       update from the user.
       
 (HTM) Bento git project repository
       
       # Listening to socket
       
       With systemd it's possible to trigger a command upon connecting on a
       socket, I made bento systemd service to listen on port TCP/51337, a
       connection would start the service "bento-update.service", and display
       the output to the TCP client.
       
       This totally works in the web browser, it's now possible to create a
       bookmark that just starts the update and give instant feedback about
       the update process.  This will be particularly useful in case of a
       debug phone session to ask the remote person to trigger an update on
       their side instead of waiting for a timer.
       
       # Status display demo
       
       It is now possible to differenciate the "not up to date" state into two
       categories:
       
       * the bento scripts were updated but not NixOS version change, this is
       called "sync pending". Changes could be distributing the updating file
       to give a new address for the remote server, so we can ensure they all
       received it.
       * the local NixOS version differs from the remote version, a rebuild is
       required, thus it's called "rebuild pending"
       
       The "sync pending" is very fast, it only need to copy the files, but
       won't rebuild anything.
       
       ```text
          machine   local version   remote version              state                                     time
          -------       ---------      -----------      -------------                                     ----
         kikimora        996vw3r6      996vw3r6 💚    sync pending 🚩       (build 5m 53s) (new config 2m 48s)
              nas        r7ips2c6      lvbajpc5 🛑 rebuild pending 🚩       (build 5m 49s) (new config 1m 45s)
             t470        ih7vxijm      ih7vxijm 💚      up to date 💚                           (build 2m 24s)
               x1        fcz1s2yp      fcz1s2yp 💚      up to date 💚                           (build 2m 37s)
       ```