munin-cron with ssh transport cannot find ssh

[ghost]

Describe the bug

services.munin-cron.hosts = '' [foo] address ssh://foo -W 127.0.0.1:4949 '';

in /var/log/munin/.munin-update-wrapped.log:

2019/10/30 14:50:58 [ERROR] Munin::Master::UpdateWorker died with 'open3: exec of ssh -o ChallengeResponseAuthentication=no -o StrictHostKeyChecking=no -p 22 foo fa\ iled: No such file or directory at /nix/store/h0g8mv9v8x4kidiq24m74s92b3ps85fl-munin-2.0.43/lib/perl5/site_perl/Munin/Master/Node.pm line 112.'

manual fix:

systemd.services.munin-cron.path = [pkgs.openssh];

To Reproduce

services.munin-cron.enable = true; and configure at least one node to which can the munin user ssh

Expected behavior should work out of the box

Metadata Please run nix run nixpkgs.nix-info -c nix-info -m and paste the result.

• system: "x86_64-linux"
• host os: Linux 4.19.80, NixOS, 19.03.173624.b6cfdceb7f9 (Koi)
• multi-user?: yes
• sandbox: yes
• version: nix-env (Nix) 2.2.2
• channels(root): "nixos-19.09.840.8bf142e001b"
• nixpkgs: /nix/var/nix/profiles/per-user/root/channels/nixos

Maintainer information:

# a list of nixpkgs attributes affected by the problem
attribute:
# a list of nixos modules affected by the problem
module:
  munin-cron

[ghost]

it would probably also be good if the ssh was automatically set up as recommended

something like

systemd.services.munin-cron-init = {
  description = "munin-cron-init";
  wantedBy = ["munin-cron.service"];
  unitConfig.RequiresMountsFor = "/var/lib/munin";
  script = ''
    if ! test -d ~munin/.ssh; then
      mkdir ~munin/.ssh
    fi
    if ! test -f ~munin/.ssh/id_ed25519; then
      ${pkgs.openssh}/bin/ssh-keygen \
        -t ed25519 \
        -f ~munin/.ssh/id_ed25519 \
        -N ""
    fi
    cat > ~munin/.ssh/config <<EOF
      # do not edit this automatically updated file
      Host *
        BatchMode=yes
        ConnectTimeout=10
        EscapeChar=none
        ExitOnForwardFailure=yes
        ForwardAgent=no
        ForwardX11=no
        IdentitiesOnly=yes
        PasswordAuthentication=no
        RequestTTY=no
        StrictHostKeyChecking=no
        User munin
    EOF
  '';
  serviceConfig = {
    User = "munin";
    Type = "oneshot";
    RemainAfterExit = true;
  };
};

maybe User should be also configurable and not hardcoded to munin

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