A work in progress backup of dovecot maildirs using rsnapshot and dsync.

rsnapshotbackup.nix

{ config, pkgs, lib, ... }:

let
  cfg = config.mailserver;

  backupUser = "tardis";

  dsyncBackupScript = "dsyncbackup.sh";

  set = cfg.loginAccounts;
  mailboxes = builtins.attrNames set;
  lines = lib.lists.imap0 (i: v: "dsync -f -o plugin/acl= -o plugin/quota= -o plugin/zlib_save= -u ${toString v} backup maildir:$WORK_DIR/${toString v}") mailboxes;
  scriptLines = builtins.concatStringsSep "\n" lines;
  script = pkgs.writeScript (toString dsyncBackupScript) ''
    #!${pkgs.stdenv.shell}
    set -e

    # create temp directory that dsync can write to
    WORK_DIR=$(mktemp -d)
    chmod o+rwx $WORK_DIR

    function cleanup {
      rm -rf "$WORK_DIR"
      echo "Deleted temp working directory $WORK_DIR"
    }

    # register cleanup
    trap cleanup EXIT

    # backs up all mailboxes to subdirectories of the current one to be picked up by rsnapshot
    ${scriptLines}

    # move content of tmp directory into current directory
    mv $WORK_DIR/* .
  '';
in {
  # dsync backup of a single mailbox
  services.rsnapshot = {
    enable = true;
    cronIntervals = {
                 # minute, hour, day-in-month, month, weekday (0 = sunday)
      "hourly" = " 0  *  *  *  *"; # Every full hour
      "daily"  = "50 21  *  *  *"; # Every day at 21:50
      "weekly" = " 0  5  *  *  0"; # Every sunday at 5:00 AM
    };
    # rsnapshot expects intervals shortest first, e.g. hourly first, then daily.
    # tabs must separate all elements
    extraConfig = ''
      #snapshot_root    /home/${backupUser}/rsnapshot
      snapshot_root /var/rsnapshot
      retain    hourly  24
      retain    daily   365
      retain    weekly  54
      backup_exec   chmod o+rx g+rx /var/rsnapshot
      backup_script ${script}   localhost/dsync/
      backup    /var/vmail/ localhost/
    '';
  };

  users.extraUsers."${backupUser}" = {
    isSystemUser = true;
    home = "/home/${backupUser}";
    createHome = true;
    extraGroups = [ ];
  };
}