[docs] add local persistent microvm usage

this now runs any host as microvm. it removes shared directories for
microvms so no manuall setup is needed (expect you want persistence).
i took it from c3d2, thanks guys for the inspiration <3
https://gitea.c3d2.de/c3d2/nix-config/src/branch/master/packages.nix

doc/src/anleitung/microvm.md

@@ -12,14 +12,44 @@ Use durruti as orientation:
 "10.0.0.5" is the IP assigned to its tap interface.  
 
 ### Testing MicroVMs locally
-MicroVMs can be built and run easily on your local host.
-For durruti this is done by:
+MicroVMs can be built and run easily on your local host, but they are not persistent!
+For durruti for example this is done by:
 ``` bash
-sudo nix run .\#nixosConfigurations.durruti.config.microvm.declaredRunner
+nix run .\#durruti-vm
+```
+
+### Testing persistent microvms
+In order to test persistent microvms locally we need to create them using the ```microvm``` command.  
+This is necessary to be able to mount persistent /etc and /var volumes on those hosts.  
+Do the following:
+
+```bash
+# go into our repo and start the default dev shell (or us direnv)
+nix develop .#
+
+# create a microvm on your host (on the example of durruti)
+sudo microvm -c durruti -f git+file:///home/username/path/to/infrastructure/repo
+
+# start the vm
+sudo systemctl start microvm@durruti.serivce
+
+# this may fail, if so we most probably need to create /var /etc manually, then restart
+sudo mkdir /var/lib/microvms/durruti/{var, etc}
+
+# now you can for example get the rsa host key from /var/lib/microvms/durruti/etc/ssh/
+
+# alternatively u can run the vm in interactive mode (maybe stop the microvm@durruti.service first)
+microvm -r durruti
+
+# after u made changes to the microvm update and restart the vm 
+microvm -uR durruti
+
+# deleting the vm again:
+sudo systemctl stop microvm@durruti.service
+sudo systemctl stop microvm-virtiofsd@durruti.service
+sudo rm -rf /var/lib/microvms/durruti
 ```
 
-It seems to be necessary to run this as root so that the according tap interface can be created.
-To be able to ping the VM or give Internet Access to the VM your host needs to be setup as described below.
 
 ### Host Setup
 

outputs.nix

@@ -56,7 +56,46 @@ in (utils.lib.eachSystem (builtins.filter filter_system utils.lib.defaultSystems
           cp -r ./book/* $dest
         '';
       };
-    };
+    } //
+
+    builtins.foldl'
+    (result: host:
+      let
+        inherit (self.nixosConfigurations.${host}) config;
+      in
+      result // {
+        # boot any machine in a microvm
+        "${host}-vm" = (self.nixosConfigurations.${host}.extendModules {
+          modules = [{
+            microvm = {
+              mem = pkgs.lib.mkForce 4096;
+              hypervisor = pkgs.lib.mkForce "qemu";
+              socket = pkgs.lib.mkForce null;
+              shares = pkgs.lib.mkForce [{
+                tag = "ro-store";
+                source = "/nix/store";
+                mountPoint = "/nix/.ro-store";
+              }];
+              interfaces = pkgs.lib.mkForce [{
+                type = "user";
+                id = "eth0";
+                mac = "02:23:de:ad:be:ef";
+              }];
+            };
+            boot.isContainer = pkgs.lib.mkForce false;
+            users.users.root.password = "";
+            fileSystems."/".fsType = pkgs.lib.mkForce "tmpfs";
+            services.getty.helpLine = ''
+              Log in as "root" with an empty password.
+              Use "reboot" to shut qemu down.
+            '';
+          }] ++ pkgs.lib.optionals (! config ? microvm) [
+            microvm.nixosModules.microvm
+          ];
+        }).config.microvm.declaredRunner;
+    })
+    { }
+    (builtins.attrNames self.nixosConfigurations);
 
     apps = {
       docs = {